Source file src/runtime/map.go

     1	// Copyright 2014 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	package runtime
     6	
     7	// This file contains the implementation of Go's map type.
     8	//
     9	// A map is just a hash table. The data is arranged
    10	// into an array of buckets. Each bucket contains up to
    11	// 8 key/elem pairs. The low-order bits of the hash are
    12	// used to select a bucket. Each bucket contains a few
    13	// high-order bits of each hash to distinguish the entries
    14	// within a single bucket.
    15	//
    16	// If more than 8 keys hash to a bucket, we chain on
    17	// extra buckets.
    18	//
    19	// When the hashtable grows, we allocate a new array
    20	// of buckets twice as big. Buckets are incrementally
    21	// copied from the old bucket array to the new bucket array.
    22	//
    23	// Map iterators walk through the array of buckets and
    24	// return the keys in walk order (bucket #, then overflow
    25	// chain order, then bucket index).  To maintain iteration
    26	// semantics, we never move keys within their bucket (if
    27	// we did, keys might be returned 0 or 2 times).  When
    28	// growing the table, iterators remain iterating through the
    29	// old table and must check the new table if the bucket
    30	// they are iterating through has been moved ("evacuated")
    31	// to the new table.
    32	
    33	// Picking loadFactor: too large and we have lots of overflow
    34	// buckets, too small and we waste a lot of space. I wrote
    35	// a simple program to check some stats for different loads:
    36	// (64-bit, 8 byte keys and elems)
    37	//  loadFactor    %overflow  bytes/entry     hitprobe    missprobe
    38	//        4.00         2.13        20.77         3.00         4.00
    39	//        4.50         4.05        17.30         3.25         4.50
    40	//        5.00         6.85        14.77         3.50         5.00
    41	//        5.50        10.55        12.94         3.75         5.50
    42	//        6.00        15.27        11.67         4.00         6.00
    43	//        6.50        20.90        10.79         4.25         6.50
    44	//        7.00        27.14        10.15         4.50         7.00
    45	//        7.50        34.03         9.73         4.75         7.50
    46	//        8.00        41.10         9.40         5.00         8.00
    47	//
    48	// %overflow   = percentage of buckets which have an overflow bucket
    49	// bytes/entry = overhead bytes used per key/elem pair
    50	// hitprobe    = # of entries to check when looking up a present key
    51	// missprobe   = # of entries to check when looking up an absent key
    52	//
    53	// Keep in mind this data is for maximally loaded tables, i.e. just
    54	// before the table grows. Typical tables will be somewhat less loaded.
    55	
    56	import (
    57		"runtime/internal/atomic"
    58		"runtime/internal/math"
    59		"runtime/internal/sys"
    60		"unsafe"
    61	)
    62	
    63	const (
    64		// Maximum number of key/elem pairs a bucket can hold.
    65		bucketCntBits = 3
    66		bucketCnt     = 1 << bucketCntBits
    67	
    68		// Maximum average load of a bucket that triggers growth is 6.5.
    69		// Represent as loadFactorNum/loadFactDen, to allow integer math.
    70		loadFactorNum = 13
    71		loadFactorDen = 2
    72	
    73		// Maximum key or elem size to keep inline (instead of mallocing per element).
    74		// Must fit in a uint8.
    75		// Fast versions cannot handle big elems - the cutoff size for
    76		// fast versions in cmd/compile/internal/gc/walk.go must be at most this elem.
    77		maxKeySize  = 128
    78		maxElemSize = 128
    79	
    80		// data offset should be the size of the bmap struct, but needs to be
    81		// aligned correctly. For amd64p32 this means 64-bit alignment
    82		// even though pointers are 32 bit.
    83		dataOffset = unsafe.Offsetof(struct {
    84			b bmap
    85			v int64
    86		}{}.v)
    87	
    88		// Possible tophash values. We reserve a few possibilities for special marks.
    89		// Each bucket (including its overflow buckets, if any) will have either all or none of its
    90		// entries in the evacuated* states (except during the evacuate() method, which only happens
    91		// during map writes and thus no one else can observe the map during that time).
    92		emptyRest      = 0 // this cell is empty, and there are no more non-empty cells at higher indexes or overflows.
    93		emptyOne       = 1 // this cell is empty
    94		evacuatedX     = 2 // key/elem is valid.  Entry has been evacuated to first half of larger table.
    95		evacuatedY     = 3 // same as above, but evacuated to second half of larger table.
    96		evacuatedEmpty = 4 // cell is empty, bucket is evacuated.
    97		minTopHash     = 5 // minimum tophash for a normal filled cell.
    98	
    99		// flags
   100		iterator     = 1 // there may be an iterator using buckets
   101		oldIterator  = 2 // there may be an iterator using oldbuckets
   102		hashWriting  = 4 // a goroutine is writing to the map
   103		sameSizeGrow = 8 // the current map growth is to a new map of the same size
   104	
   105		// sentinel bucket ID for iterator checks
   106		noCheck = 1<<(8*sys.PtrSize) - 1
   107	)
   108	
   109	// isEmpty reports whether the given tophash array entry represents an empty bucket entry.
   110	func isEmpty(x uint8) bool {
   111		return x <= emptyOne
   112	}
   113	
   114	// A header for a Go map.
   115	type hmap struct {
   116		// Note: the format of the hmap is also encoded in cmd/compile/internal/gc/reflect.go.
   117		// Make sure this stays in sync with the compiler's definition.
   118		count     int // # live cells == size of map.  Must be first (used by len() builtin)
   119		flags     uint8
   120		B         uint8  // log_2 of # of buckets (can hold up to loadFactor * 2^B items)
   121		noverflow uint16 // approximate number of overflow buckets; see incrnoverflow for details
   122		hash0     uint32 // hash seed
   123	
   124		buckets    unsafe.Pointer // array of 2^B Buckets. may be nil if count==0.
   125		oldbuckets unsafe.Pointer // previous bucket array of half the size, non-nil only when growing
   126		nevacuate  uintptr        // progress counter for evacuation (buckets less than this have been evacuated)
   127	
   128		extra *mapextra // optional fields
   129	}
   130	
   131	// mapextra holds fields that are not present on all maps.
   132	type mapextra struct {
   133		// If both key and elem do not contain pointers and are inline, then we mark bucket
   134		// type as containing no pointers. This avoids scanning such maps.
   135		// However, bmap.overflow is a pointer. In order to keep overflow buckets
   136		// alive, we store pointers to all overflow buckets in hmap.extra.overflow and hmap.extra.oldoverflow.
   137		// overflow and oldoverflow are only used if key and elem do not contain pointers.
   138		// overflow contains overflow buckets for hmap.buckets.
   139		// oldoverflow contains overflow buckets for hmap.oldbuckets.
   140		// The indirection allows to store a pointer to the slice in hiter.
   141		overflow    *[]*bmap
   142		oldoverflow *[]*bmap
   143	
   144		// nextOverflow holds a pointer to a free overflow bucket.
   145		nextOverflow *bmap
   146	}
   147	
   148	// A bucket for a Go map.
   149	type bmap struct {
   150		// tophash generally contains the top byte of the hash value
   151		// for each key in this bucket. If tophash[0] < minTopHash,
   152		// tophash[0] is a bucket evacuation state instead.
   153		tophash [bucketCnt]uint8
   154		// Followed by bucketCnt keys and then bucketCnt elems.
   155		// NOTE: packing all the keys together and then all the elems together makes the
   156		// code a bit more complicated than alternating key/elem/key/elem/... but it allows
   157		// us to eliminate padding which would be needed for, e.g., map[int64]int8.
   158		// Followed by an overflow pointer.
   159	}
   160	
   161	// A hash iteration structure.
   162	// If you modify hiter, also change cmd/compile/internal/gc/reflect.go to indicate
   163	// the layout of this structure.
   164	type hiter struct {
   165		key         unsafe.Pointer // Must be in first position.  Write nil to indicate iteration end (see cmd/internal/gc/range.go).
   166		elem        unsafe.Pointer // Must be in second position (see cmd/internal/gc/range.go).
   167		t           *maptype
   168		h           *hmap
   169		buckets     unsafe.Pointer // bucket ptr at hash_iter initialization time
   170		bptr        *bmap          // current bucket
   171		overflow    *[]*bmap       // keeps overflow buckets of hmap.buckets alive
   172		oldoverflow *[]*bmap       // keeps overflow buckets of hmap.oldbuckets alive
   173		startBucket uintptr        // bucket iteration started at
   174		offset      uint8          // intra-bucket offset to start from during iteration (should be big enough to hold bucketCnt-1)
   175		wrapped     bool           // already wrapped around from end of bucket array to beginning
   176		B           uint8
   177		i           uint8
   178		bucket      uintptr
   179		checkBucket uintptr
   180	}
   181	
   182	// bucketShift returns 1<<b, optimized for code generation.
   183	func bucketShift(b uint8) uintptr {
   184		// Masking the shift amount allows overflow checks to be elided.
   185		return uintptr(1) << (b & (sys.PtrSize*8 - 1))
   186	}
   187	
   188	// bucketMask returns 1<<b - 1, optimized for code generation.
   189	func bucketMask(b uint8) uintptr {
   190		return bucketShift(b) - 1
   191	}
   192	
   193	// tophash calculates the tophash value for hash.
   194	func tophash(hash uintptr) uint8 {
   195		top := uint8(hash >> (sys.PtrSize*8 - 8))
   196		if top < minTopHash {
   197			top += minTopHash
   198		}
   199		return top
   200	}
   201	
   202	func evacuated(b *bmap) bool {
   203		h := b.tophash[0]
   204		return h > emptyOne && h < minTopHash
   205	}
   206	
   207	func (b *bmap) overflow(t *maptype) *bmap {
   208		return *(**bmap)(add(unsafe.Pointer(b), uintptr(t.bucketsize)-sys.PtrSize))
   209	}
   210	
   211	func (b *bmap) setoverflow(t *maptype, ovf *bmap) {
   212		*(**bmap)(add(unsafe.Pointer(b), uintptr(t.bucketsize)-sys.PtrSize)) = ovf
   213	}
   214	
   215	func (b *bmap) keys() unsafe.Pointer {
   216		return add(unsafe.Pointer(b), dataOffset)
   217	}
   218	
   219	// incrnoverflow increments h.noverflow.
   220	// noverflow counts the number of overflow buckets.
   221	// This is used to trigger same-size map growth.
   222	// See also tooManyOverflowBuckets.
   223	// To keep hmap small, noverflow is a uint16.
   224	// When there are few buckets, noverflow is an exact count.
   225	// When there are many buckets, noverflow is an approximate count.
   226	func (h *hmap) incrnoverflow() {
   227		// We trigger same-size map growth if there are
   228		// as many overflow buckets as buckets.
   229		// We need to be able to count to 1<<h.B.
   230		if h.B < 16 {
   231			h.noverflow++
   232			return
   233		}
   234		// Increment with probability 1/(1<<(h.B-15)).
   235		// When we reach 1<<15 - 1, we will have approximately
   236		// as many overflow buckets as buckets.
   237		mask := uint32(1)<<(h.B-15) - 1
   238		// Example: if h.B == 18, then mask == 7,
   239		// and fastrand & 7 == 0 with probability 1/8.
   240		if fastrand()&mask == 0 {
   241			h.noverflow++
   242		}
   243	}
   244	
   245	func (h *hmap) newoverflow(t *maptype, b *bmap) *bmap {
   246		var ovf *bmap
   247		if h.extra != nil && h.extra.nextOverflow != nil {
   248			// We have preallocated overflow buckets available.
   249			// See makeBucketArray for more details.
   250			ovf = h.extra.nextOverflow
   251			if ovf.overflow(t) == nil {
   252				// We're not at the end of the preallocated overflow buckets. Bump the pointer.
   253				h.extra.nextOverflow = (*bmap)(add(unsafe.Pointer(ovf), uintptr(t.bucketsize)))
   254			} else {
   255				// This is the last preallocated overflow bucket.
   256				// Reset the overflow pointer on this bucket,
   257				// which was set to a non-nil sentinel value.
   258				ovf.setoverflow(t, nil)
   259				h.extra.nextOverflow = nil
   260			}
   261		} else {
   262			ovf = (*bmap)(newobject(t.bucket))
   263		}
   264		h.incrnoverflow()
   265		if t.bucket.ptrdata == 0 {
   266			h.createOverflow()
   267			*h.extra.overflow = append(*h.extra.overflow, ovf)
   268		}
   269		b.setoverflow(t, ovf)
   270		return ovf
   271	}
   272	
   273	func (h *hmap) createOverflow() {
   274		if h.extra == nil {
   275			h.extra = new(mapextra)
   276		}
   277		if h.extra.overflow == nil {
   278			h.extra.overflow = new([]*bmap)
   279		}
   280	}
   281	
   282	func makemap64(t *maptype, hint int64, h *hmap) *hmap {
   283		if int64(int(hint)) != hint {
   284			hint = 0
   285		}
   286		return makemap(t, int(hint), h)
   287	}
   288	
   289	// makemap_small implements Go map creation for make(map[k]v) and
   290	// make(map[k]v, hint) when hint is known to be at most bucketCnt
   291	// at compile time and the map needs to be allocated on the heap.
   292	func makemap_small() *hmap {
   293		h := new(hmap)
   294		h.hash0 = fastrand()
   295		return h
   296	}
   297	
   298	// makemap implements Go map creation for make(map[k]v, hint).
   299	// If the compiler has determined that the map or the first bucket
   300	// can be created on the stack, h and/or bucket may be non-nil.
   301	// If h != nil, the map can be created directly in h.
   302	// If h.buckets != nil, bucket pointed to can be used as the first bucket.
   303	func makemap(t *maptype, hint int, h *hmap) *hmap {
   304		mem, overflow := math.MulUintptr(uintptr(hint), t.bucket.size)
   305		if overflow || mem > maxAlloc {
   306			hint = 0
   307		}
   308	
   309		// initialize Hmap
   310		if h == nil {
   311			h = new(hmap)
   312		}
   313		h.hash0 = fastrand()
   314	
   315		// Find the size parameter B which will hold the requested # of elements.
   316		// For hint < 0 overLoadFactor returns false since hint < bucketCnt.
   317		B := uint8(0)
   318		for overLoadFactor(hint, B) {
   319			B++
   320		}
   321		h.B = B
   322	
   323		// allocate initial hash table
   324		// if B == 0, the buckets field is allocated lazily later (in mapassign)
   325		// If hint is large zeroing this memory could take a while.
   326		if h.B != 0 {
   327			var nextOverflow *bmap
   328			h.buckets, nextOverflow = makeBucketArray(t, h.B, nil)
   329			if nextOverflow != nil {
   330				h.extra = new(mapextra)
   331				h.extra.nextOverflow = nextOverflow
   332			}
   333		}
   334	
   335		return h
   336	}
   337	
   338	// makeBucketArray initializes a backing array for map buckets.
   339	// 1<<b is the minimum number of buckets to allocate.
   340	// dirtyalloc should either be nil or a bucket array previously
   341	// allocated by makeBucketArray with the same t and b parameters.
   342	// If dirtyalloc is nil a new backing array will be alloced and
   343	// otherwise dirtyalloc will be cleared and reused as backing array.
   344	func makeBucketArray(t *maptype, b uint8, dirtyalloc unsafe.Pointer) (buckets unsafe.Pointer, nextOverflow *bmap) {
   345		base := bucketShift(b)
   346		nbuckets := base
   347		// For small b, overflow buckets are unlikely.
   348		// Avoid the overhead of the calculation.
   349		if b >= 4 {
   350			// Add on the estimated number of overflow buckets
   351			// required to insert the median number of elements
   352			// used with this value of b.
   353			nbuckets += bucketShift(b - 4)
   354			sz := t.bucket.size * nbuckets
   355			up := roundupsize(sz)
   356			if up != sz {
   357				nbuckets = up / t.bucket.size
   358			}
   359		}
   360	
   361		if dirtyalloc == nil {
   362			buckets = newarray(t.bucket, int(nbuckets))
   363		} else {
   364			// dirtyalloc was previously generated by
   365			// the above newarray(t.bucket, int(nbuckets))
   366			// but may not be empty.
   367			buckets = dirtyalloc
   368			size := t.bucket.size * nbuckets
   369			if t.bucket.ptrdata != 0 {
   370				memclrHasPointers(buckets, size)
   371			} else {
   372				memclrNoHeapPointers(buckets, size)
   373			}
   374		}
   375	
   376		if base != nbuckets {
   377			// We preallocated some overflow buckets.
   378			// To keep the overhead of tracking these overflow buckets to a minimum,
   379			// we use the convention that if a preallocated overflow bucket's overflow
   380			// pointer is nil, then there are more available by bumping the pointer.
   381			// We need a safe non-nil pointer for the last overflow bucket; just use buckets.
   382			nextOverflow = (*bmap)(add(buckets, base*uintptr(t.bucketsize)))
   383			last := (*bmap)(add(buckets, (nbuckets-1)*uintptr(t.bucketsize)))
   384			last.setoverflow(t, (*bmap)(buckets))
   385		}
   386		return buckets, nextOverflow
   387	}
   388	
   389	// mapaccess1 returns a pointer to h[key].  Never returns nil, instead
   390	// it will return a reference to the zero object for the elem type if
   391	// the key is not in the map.
   392	// NOTE: The returned pointer may keep the whole map live, so don't
   393	// hold onto it for very long.
   394	func mapaccess1(t *maptype, h *hmap, key unsafe.Pointer) unsafe.Pointer {
   395		if raceenabled && h != nil {
   396			callerpc := getcallerpc()
   397			pc := funcPC(mapaccess1)
   398			racereadpc(unsafe.Pointer(h), callerpc, pc)
   399			raceReadObjectPC(t.key, key, callerpc, pc)
   400		}
   401		if msanenabled && h != nil {
   402			msanread(key, t.key.size)
   403		}
   404		if h == nil || h.count == 0 {
   405			if t.hashMightPanic() {
   406				t.key.alg.hash(key, 0) // see issue 23734
   407			}
   408			return unsafe.Pointer(&zeroVal[0])
   409		}
   410		if h.flags&hashWriting != 0 {
   411			throw("concurrent map read and map write")
   412		}
   413		alg := t.key.alg
   414		hash := alg.hash(key, uintptr(h.hash0))
   415		m := bucketMask(h.B)
   416		b := (*bmap)(add(h.buckets, (hash&m)*uintptr(t.bucketsize)))
   417		if c := h.oldbuckets; c != nil {
   418			if !h.sameSizeGrow() {
   419				// There used to be half as many buckets; mask down one more power of two.
   420				m >>= 1
   421			}
   422			oldb := (*bmap)(add(c, (hash&m)*uintptr(t.bucketsize)))
   423			if !evacuated(oldb) {
   424				b = oldb
   425			}
   426		}
   427		top := tophash(hash)
   428	bucketloop:
   429		for ; b != nil; b = b.overflow(t) {
   430			for i := uintptr(0); i < bucketCnt; i++ {
   431				if b.tophash[i] != top {
   432					if b.tophash[i] == emptyRest {
   433						break bucketloop
   434					}
   435					continue
   436				}
   437				k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
   438				if t.indirectkey() {
   439					k = *((*unsafe.Pointer)(k))
   440				}
   441				if alg.equal(key, k) {
   442					e := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.elemsize))
   443					if t.indirectelem() {
   444						e = *((*unsafe.Pointer)(e))
   445					}
   446					return e
   447				}
   448			}
   449		}
   450		return unsafe.Pointer(&zeroVal[0])
   451	}
   452	
   453	func mapaccess2(t *maptype, h *hmap, key unsafe.Pointer) (unsafe.Pointer, bool) {
   454		if raceenabled && h != nil {
   455			callerpc := getcallerpc()
   456			pc := funcPC(mapaccess2)
   457			racereadpc(unsafe.Pointer(h), callerpc, pc)
   458			raceReadObjectPC(t.key, key, callerpc, pc)
   459		}
   460		if msanenabled && h != nil {
   461			msanread(key, t.key.size)
   462		}
   463		if h == nil || h.count == 0 {
   464			if t.hashMightPanic() {
   465				t.key.alg.hash(key, 0) // see issue 23734
   466			}
   467			return unsafe.Pointer(&zeroVal[0]), false
   468		}
   469		if h.flags&hashWriting != 0 {
   470			throw("concurrent map read and map write")
   471		}
   472		alg := t.key.alg
   473		hash := alg.hash(key, uintptr(h.hash0))
   474		m := bucketMask(h.B)
   475		b := (*bmap)(unsafe.Pointer(uintptr(h.buckets) + (hash&m)*uintptr(t.bucketsize)))
   476		if c := h.oldbuckets; c != nil {
   477			if !h.sameSizeGrow() {
   478				// There used to be half as many buckets; mask down one more power of two.
   479				m >>= 1
   480			}
   481			oldb := (*bmap)(unsafe.Pointer(uintptr(c) + (hash&m)*uintptr(t.bucketsize)))
   482			if !evacuated(oldb) {
   483				b = oldb
   484			}
   485		}
   486		top := tophash(hash)
   487	bucketloop:
   488		for ; b != nil; b = b.overflow(t) {
   489			for i := uintptr(0); i < bucketCnt; i++ {
   490				if b.tophash[i] != top {
   491					if b.tophash[i] == emptyRest {
   492						break bucketloop
   493					}
   494					continue
   495				}
   496				k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
   497				if t.indirectkey() {
   498					k = *((*unsafe.Pointer)(k))
   499				}
   500				if alg.equal(key, k) {
   501					e := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.elemsize))
   502					if t.indirectelem() {
   503						e = *((*unsafe.Pointer)(e))
   504					}
   505					return e, true
   506				}
   507			}
   508		}
   509		return unsafe.Pointer(&zeroVal[0]), false
   510	}
   511	
   512	// returns both key and elem. Used by map iterator
   513	func mapaccessK(t *maptype, h *hmap, key unsafe.Pointer) (unsafe.Pointer, unsafe.Pointer) {
   514		if h == nil || h.count == 0 {
   515			return nil, nil
   516		}
   517		alg := t.key.alg
   518		hash := alg.hash(key, uintptr(h.hash0))
   519		m := bucketMask(h.B)
   520		b := (*bmap)(unsafe.Pointer(uintptr(h.buckets) + (hash&m)*uintptr(t.bucketsize)))
   521		if c := h.oldbuckets; c != nil {
   522			if !h.sameSizeGrow() {
   523				// There used to be half as many buckets; mask down one more power of two.
   524				m >>= 1
   525			}
   526			oldb := (*bmap)(unsafe.Pointer(uintptr(c) + (hash&m)*uintptr(t.bucketsize)))
   527			if !evacuated(oldb) {
   528				b = oldb
   529			}
   530		}
   531		top := tophash(hash)
   532	bucketloop:
   533		for ; b != nil; b = b.overflow(t) {
   534			for i := uintptr(0); i < bucketCnt; i++ {
   535				if b.tophash[i] != top {
   536					if b.tophash[i] == emptyRest {
   537						break bucketloop
   538					}
   539					continue
   540				}
   541				k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
   542				if t.indirectkey() {
   543					k = *((*unsafe.Pointer)(k))
   544				}
   545				if alg.equal(key, k) {
   546					e := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.elemsize))
   547					if t.indirectelem() {
   548						e = *((*unsafe.Pointer)(e))
   549					}
   550					return k, e
   551				}
   552			}
   553		}
   554		return nil, nil
   555	}
   556	
   557	func mapaccess1_fat(t *maptype, h *hmap, key, zero unsafe.Pointer) unsafe.Pointer {
   558		e := mapaccess1(t, h, key)
   559		if e == unsafe.Pointer(&zeroVal[0]) {
   560			return zero
   561		}
   562		return e
   563	}
   564	
   565	func mapaccess2_fat(t *maptype, h *hmap, key, zero unsafe.Pointer) (unsafe.Pointer, bool) {
   566		e := mapaccess1(t, h, key)
   567		if e == unsafe.Pointer(&zeroVal[0]) {
   568			return zero, false
   569		}
   570		return e, true
   571	}
   572	
   573	// Like mapaccess, but allocates a slot for the key if it is not present in the map.
   574	func mapassign(t *maptype, h *hmap, key unsafe.Pointer) unsafe.Pointer {
   575		if h == nil {
   576			panic(plainError("assignment to entry in nil map"))
   577		}
   578		if raceenabled {
   579			callerpc := getcallerpc()
   580			pc := funcPC(mapassign)
   581			racewritepc(unsafe.Pointer(h), callerpc, pc)
   582			raceReadObjectPC(t.key, key, callerpc, pc)
   583		}
   584		if msanenabled {
   585			msanread(key, t.key.size)
   586		}
   587		if h.flags&hashWriting != 0 {
   588			throw("concurrent map writes")
   589		}
   590		alg := t.key.alg
   591		hash := alg.hash(key, uintptr(h.hash0))
   592	
   593		// Set hashWriting after calling alg.hash, since alg.hash may panic,
   594		// in which case we have not actually done a write.
   595		h.flags ^= hashWriting
   596	
   597		if h.buckets == nil {
   598			h.buckets = newobject(t.bucket) // newarray(t.bucket, 1)
   599		}
   600	
   601	again:
   602		bucket := hash & bucketMask(h.B)
   603		if h.growing() {
   604			growWork(t, h, bucket)
   605		}
   606		b := (*bmap)(unsafe.Pointer(uintptr(h.buckets) + bucket*uintptr(t.bucketsize)))
   607		top := tophash(hash)
   608	
   609		var inserti *uint8
   610		var insertk unsafe.Pointer
   611		var elem unsafe.Pointer
   612	bucketloop:
   613		for {
   614			for i := uintptr(0); i < bucketCnt; i++ {
   615				if b.tophash[i] != top {
   616					if isEmpty(b.tophash[i]) && inserti == nil {
   617						inserti = &b.tophash[i]
   618						insertk = add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
   619						elem = add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.elemsize))
   620					}
   621					if b.tophash[i] == emptyRest {
   622						break bucketloop
   623					}
   624					continue
   625				}
   626				k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
   627				if t.indirectkey() {
   628					k = *((*unsafe.Pointer)(k))
   629				}
   630				if !alg.equal(key, k) {
   631					continue
   632				}
   633				// already have a mapping for key. Update it.
   634				if t.needkeyupdate() {
   635					typedmemmove(t.key, k, key)
   636				}
   637				elem = add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.elemsize))
   638				goto done
   639			}
   640			ovf := b.overflow(t)
   641			if ovf == nil {
   642				break
   643			}
   644			b = ovf
   645		}
   646	
   647		// Did not find mapping for key. Allocate new cell & add entry.
   648	
   649		// If we hit the max load factor or we have too many overflow buckets,
   650		// and we're not already in the middle of growing, start growing.
   651		if !h.growing() && (overLoadFactor(h.count+1, h.B) || tooManyOverflowBuckets(h.noverflow, h.B)) {
   652			hashGrow(t, h)
   653			goto again // Growing the table invalidates everything, so try again
   654		}
   655	
   656		if inserti == nil {
   657			// all current buckets are full, allocate a new one.
   658			newb := h.newoverflow(t, b)
   659			inserti = &newb.tophash[0]
   660			insertk = add(unsafe.Pointer(newb), dataOffset)
   661			elem = add(insertk, bucketCnt*uintptr(t.keysize))
   662		}
   663	
   664		// store new key/elem at insert position
   665		if t.indirectkey() {
   666			kmem := newobject(t.key)
   667			*(*unsafe.Pointer)(insertk) = kmem
   668			insertk = kmem
   669		}
   670		if t.indirectelem() {
   671			vmem := newobject(t.elem)
   672			*(*unsafe.Pointer)(elem) = vmem
   673		}
   674		typedmemmove(t.key, insertk, key)
   675		*inserti = top
   676		h.count++
   677	
   678	done:
   679		if h.flags&hashWriting == 0 {
   680			throw("concurrent map writes")
   681		}
   682		h.flags &^= hashWriting
   683		if t.indirectelem() {
   684			elem = *((*unsafe.Pointer)(elem))
   685		}
   686		return elem
   687	}
   688	
   689	func mapdelete(t *maptype, h *hmap, key unsafe.Pointer) {
   690		if raceenabled && h != nil {
   691			callerpc := getcallerpc()
   692			pc := funcPC(mapdelete)
   693			racewritepc(unsafe.Pointer(h), callerpc, pc)
   694			raceReadObjectPC(t.key, key, callerpc, pc)
   695		}
   696		if msanenabled && h != nil {
   697			msanread(key, t.key.size)
   698		}
   699		if h == nil || h.count == 0 {
   700			if t.hashMightPanic() {
   701				t.key.alg.hash(key, 0) // see issue 23734
   702			}
   703			return
   704		}
   705		if h.flags&hashWriting != 0 {
   706			throw("concurrent map writes")
   707		}
   708	
   709		alg := t.key.alg
   710		hash := alg.hash(key, uintptr(h.hash0))
   711	
   712		// Set hashWriting after calling alg.hash, since alg.hash may panic,
   713		// in which case we have not actually done a write (delete).
   714		h.flags ^= hashWriting
   715	
   716		bucket := hash & bucketMask(h.B)
   717		if h.growing() {
   718			growWork(t, h, bucket)
   719		}
   720		b := (*bmap)(add(h.buckets, bucket*uintptr(t.bucketsize)))
   721		bOrig := b
   722		top := tophash(hash)
   723	search:
   724		for ; b != nil; b = b.overflow(t) {
   725			for i := uintptr(0); i < bucketCnt; i++ {
   726				if b.tophash[i] != top {
   727					if b.tophash[i] == emptyRest {
   728						break search
   729					}
   730					continue
   731				}
   732				k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
   733				k2 := k
   734				if t.indirectkey() {
   735					k2 = *((*unsafe.Pointer)(k2))
   736				}
   737				if !alg.equal(key, k2) {
   738					continue
   739				}
   740				// Only clear key if there are pointers in it.
   741				if t.indirectkey() {
   742					*(*unsafe.Pointer)(k) = nil
   743				} else if t.key.ptrdata != 0 {
   744					memclrHasPointers(k, t.key.size)
   745				}
   746				e := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.elemsize))
   747				if t.indirectelem() {
   748					*(*unsafe.Pointer)(e) = nil
   749				} else if t.elem.ptrdata != 0 {
   750					memclrHasPointers(e, t.elem.size)
   751				} else {
   752					memclrNoHeapPointers(e, t.elem.size)
   753				}
   754				b.tophash[i] = emptyOne
   755				// If the bucket now ends in a bunch of emptyOne states,
   756				// change those to emptyRest states.
   757				// It would be nice to make this a separate function, but
   758				// for loops are not currently inlineable.
   759				if i == bucketCnt-1 {
   760					if b.overflow(t) != nil && b.overflow(t).tophash[0] != emptyRest {
   761						goto notLast
   762					}
   763				} else {
   764					if b.tophash[i+1] != emptyRest {
   765						goto notLast
   766					}
   767				}
   768				for {
   769					b.tophash[i] = emptyRest
   770					if i == 0 {
   771						if b == bOrig {
   772							break // beginning of initial bucket, we're done.
   773						}
   774						// Find previous bucket, continue at its last entry.
   775						c := b
   776						for b = bOrig; b.overflow(t) != c; b = b.overflow(t) {
   777						}
   778						i = bucketCnt - 1
   779					} else {
   780						i--
   781					}
   782					if b.tophash[i] != emptyOne {
   783						break
   784					}
   785				}
   786			notLast:
   787				h.count--
   788				break search
   789			}
   790		}
   791	
   792		if h.flags&hashWriting == 0 {
   793			throw("concurrent map writes")
   794		}
   795		h.flags &^= hashWriting
   796	}
   797	
   798	// mapiterinit initializes the hiter struct used for ranging over maps.
   799	// The hiter struct pointed to by 'it' is allocated on the stack
   800	// by the compilers order pass or on the heap by reflect_mapiterinit.
   801	// Both need to have zeroed hiter since the struct contains pointers.
   802	func mapiterinit(t *maptype, h *hmap, it *hiter) {
   803		if raceenabled && h != nil {
   804			callerpc := getcallerpc()
   805			racereadpc(unsafe.Pointer(h), callerpc, funcPC(mapiterinit))
   806		}
   807	
   808		if h == nil || h.count == 0 {
   809			return
   810		}
   811	
   812		if unsafe.Sizeof(hiter{})/sys.PtrSize != 12 {
   813			throw("hash_iter size incorrect") // see cmd/compile/internal/gc/reflect.go
   814		}
   815		it.t = t
   816		it.h = h
   817	
   818		// grab snapshot of bucket state
   819		it.B = h.B
   820		it.buckets = h.buckets
   821		if t.bucket.ptrdata == 0 {
   822			// Allocate the current slice and remember pointers to both current and old.
   823			// This preserves all relevant overflow buckets alive even if
   824			// the table grows and/or overflow buckets are added to the table
   825			// while we are iterating.
   826			h.createOverflow()
   827			it.overflow = h.extra.overflow
   828			it.oldoverflow = h.extra.oldoverflow
   829		}
   830	
   831		// decide where to start
   832		r := uintptr(fastrand())
   833		if h.B > 31-bucketCntBits {
   834			r += uintptr(fastrand()) << 31
   835		}
   836		it.startBucket = r & bucketMask(h.B)
   837		it.offset = uint8(r >> h.B & (bucketCnt - 1))
   838	
   839		// iterator state
   840		it.bucket = it.startBucket
   841	
   842		// Remember we have an iterator.
   843		// Can run concurrently with another mapiterinit().
   844		if old := h.flags; old&(iterator|oldIterator) != iterator|oldIterator {
   845			atomic.Or8(&h.flags, iterator|oldIterator)
   846		}
   847	
   848		mapiternext(it)
   849	}
   850	
   851	func mapiternext(it *hiter) {
   852		h := it.h
   853		if raceenabled {
   854			callerpc := getcallerpc()
   855			racereadpc(unsafe.Pointer(h), callerpc, funcPC(mapiternext))
   856		}
   857		if h.flags&hashWriting != 0 {
   858			throw("concurrent map iteration and map write")
   859		}
   860		t := it.t
   861		bucket := it.bucket
   862		b := it.bptr
   863		i := it.i
   864		checkBucket := it.checkBucket
   865		alg := t.key.alg
   866	
   867	next:
   868		if b == nil {
   869			if bucket == it.startBucket && it.wrapped {
   870				// end of iteration
   871				it.key = nil
   872				it.elem = nil
   873				return
   874			}
   875			if h.growing() && it.B == h.B {
   876				// Iterator was started in the middle of a grow, and the grow isn't done yet.
   877				// If the bucket we're looking at hasn't been filled in yet (i.e. the old
   878				// bucket hasn't been evacuated) then we need to iterate through the old
   879				// bucket and only return the ones that will be migrated to this bucket.
   880				oldbucket := bucket & it.h.oldbucketmask()
   881				b = (*bmap)(add(h.oldbuckets, oldbucket*uintptr(t.bucketsize)))
   882				if !evacuated(b) {
   883					checkBucket = bucket
   884				} else {
   885					b = (*bmap)(add(it.buckets, bucket*uintptr(t.bucketsize)))
   886					checkBucket = noCheck
   887				}
   888			} else {
   889				b = (*bmap)(add(it.buckets, bucket*uintptr(t.bucketsize)))
   890				checkBucket = noCheck
   891			}
   892			bucket++
   893			if bucket == bucketShift(it.B) {
   894				bucket = 0
   895				it.wrapped = true
   896			}
   897			i = 0
   898		}
   899		for ; i < bucketCnt; i++ {
   900			offi := (i + it.offset) & (bucketCnt - 1)
   901			if isEmpty(b.tophash[offi]) || b.tophash[offi] == evacuatedEmpty {
   902				// TODO: emptyRest is hard to use here, as we start iterating
   903				// in the middle of a bucket. It's feasible, just tricky.
   904				continue
   905			}
   906			k := add(unsafe.Pointer(b), dataOffset+uintptr(offi)*uintptr(t.keysize))
   907			if t.indirectkey() {
   908				k = *((*unsafe.Pointer)(k))
   909			}
   910			e := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+uintptr(offi)*uintptr(t.elemsize))
   911			if checkBucket != noCheck && !h.sameSizeGrow() {
   912				// Special case: iterator was started during a grow to a larger size
   913				// and the grow is not done yet. We're working on a bucket whose
   914				// oldbucket has not been evacuated yet. Or at least, it wasn't
   915				// evacuated when we started the bucket. So we're iterating
   916				// through the oldbucket, skipping any keys that will go
   917				// to the other new bucket (each oldbucket expands to two
   918				// buckets during a grow).
   919				if t.reflexivekey() || alg.equal(k, k) {
   920					// If the item in the oldbucket is not destined for
   921					// the current new bucket in the iteration, skip it.
   922					hash := alg.hash(k, uintptr(h.hash0))
   923					if hash&bucketMask(it.B) != checkBucket {
   924						continue
   925					}
   926				} else {
   927					// Hash isn't repeatable if k != k (NaNs).  We need a
   928					// repeatable and randomish choice of which direction
   929					// to send NaNs during evacuation. We'll use the low
   930					// bit of tophash to decide which way NaNs go.
   931					// NOTE: this case is why we need two evacuate tophash
   932					// values, evacuatedX and evacuatedY, that differ in
   933					// their low bit.
   934					if checkBucket>>(it.B-1) != uintptr(b.tophash[offi]&1) {
   935						continue
   936					}
   937				}
   938			}
   939			if (b.tophash[offi] != evacuatedX && b.tophash[offi] != evacuatedY) ||
   940				!(t.reflexivekey() || alg.equal(k, k)) {
   941				// This is the golden data, we can return it.
   942				// OR
   943				// key!=key, so the entry can't be deleted or updated, so we can just return it.
   944				// That's lucky for us because when key!=key we can't look it up successfully.
   945				it.key = k
   946				if t.indirectelem() {
   947					e = *((*unsafe.Pointer)(e))
   948				}
   949				it.elem = e
   950			} else {
   951				// The hash table has grown since the iterator was started.
   952				// The golden data for this key is now somewhere else.
   953				// Check the current hash table for the data.
   954				// This code handles the case where the key
   955				// has been deleted, updated, or deleted and reinserted.
   956				// NOTE: we need to regrab the key as it has potentially been
   957				// updated to an equal() but not identical key (e.g. +0.0 vs -0.0).
   958				rk, re := mapaccessK(t, h, k)
   959				if rk == nil {
   960					continue // key has been deleted
   961				}
   962				it.key = rk
   963				it.elem = re
   964			}
   965			it.bucket = bucket
   966			if it.bptr != b { // avoid unnecessary write barrier; see issue 14921
   967				it.bptr = b
   968			}
   969			it.i = i + 1
   970			it.checkBucket = checkBucket
   971			return
   972		}
   973		b = b.overflow(t)
   974		i = 0
   975		goto next
   976	}
   977	
   978	// mapclear deletes all keys from a map.
   979	func mapclear(t *maptype, h *hmap) {
   980		if raceenabled && h != nil {
   981			callerpc := getcallerpc()
   982			pc := funcPC(mapclear)
   983			racewritepc(unsafe.Pointer(h), callerpc, pc)
   984		}
   985	
   986		if h == nil || h.count == 0 {
   987			return
   988		}
   989	
   990		if h.flags&hashWriting != 0 {
   991			throw("concurrent map writes")
   992		}
   993	
   994		h.flags ^= hashWriting
   995	
   996		h.flags &^= sameSizeGrow
   997		h.oldbuckets = nil
   998		h.nevacuate = 0
   999		h.noverflow = 0
  1000		h.count = 0
  1001	
  1002		// Keep the mapextra allocation but clear any extra information.
  1003		if h.extra != nil {
  1004			*h.extra = mapextra{}
  1005		}
  1006	
  1007		// makeBucketArray clears the memory pointed to by h.buckets
  1008		// and recovers any overflow buckets by generating them
  1009		// as if h.buckets was newly alloced.
  1010		_, nextOverflow := makeBucketArray(t, h.B, h.buckets)
  1011		if nextOverflow != nil {
  1012			// If overflow buckets are created then h.extra
  1013			// will have been allocated during initial bucket creation.
  1014			h.extra.nextOverflow = nextOverflow
  1015		}
  1016	
  1017		if h.flags&hashWriting == 0 {
  1018			throw("concurrent map writes")
  1019		}
  1020		h.flags &^= hashWriting
  1021	}
  1022	
  1023	func hashGrow(t *maptype, h *hmap) {
  1024		// If we've hit the load factor, get bigger.
  1025		// Otherwise, there are too many overflow buckets,
  1026		// so keep the same number of buckets and "grow" laterally.
  1027		bigger := uint8(1)
  1028		if !overLoadFactor(h.count+1, h.B) {
  1029			bigger = 0
  1030			h.flags |= sameSizeGrow
  1031		}
  1032		oldbuckets := h.buckets
  1033		newbuckets, nextOverflow := makeBucketArray(t, h.B+bigger, nil)
  1034	
  1035		flags := h.flags &^ (iterator | oldIterator)
  1036		if h.flags&iterator != 0 {
  1037			flags |= oldIterator
  1038		}
  1039		// commit the grow (atomic wrt gc)
  1040		h.B += bigger
  1041		h.flags = flags
  1042		h.oldbuckets = oldbuckets
  1043		h.buckets = newbuckets
  1044		h.nevacuate = 0
  1045		h.noverflow = 0
  1046	
  1047		if h.extra != nil && h.extra.overflow != nil {
  1048			// Promote current overflow buckets to the old generation.
  1049			if h.extra.oldoverflow != nil {
  1050				throw("oldoverflow is not nil")
  1051			}
  1052			h.extra.oldoverflow = h.extra.overflow
  1053			h.extra.overflow = nil
  1054		}
  1055		if nextOverflow != nil {
  1056			if h.extra == nil {
  1057				h.extra = new(mapextra)
  1058			}
  1059			h.extra.nextOverflow = nextOverflow
  1060		}
  1061	
  1062		// the actual copying of the hash table data is done incrementally
  1063		// by growWork() and evacuate().
  1064	}
  1065	
  1066	// overLoadFactor reports whether count items placed in 1<<B buckets is over loadFactor.
  1067	func overLoadFactor(count int, B uint8) bool {
  1068		return count > bucketCnt && uintptr(count) > loadFactorNum*(bucketShift(B)/loadFactorDen)
  1069	}
  1070	
  1071	// tooManyOverflowBuckets reports whether noverflow buckets is too many for a map with 1<<B buckets.
  1072	// Note that most of these overflow buckets must be in sparse use;
  1073	// if use was dense, then we'd have already triggered regular map growth.
  1074	func tooManyOverflowBuckets(noverflow uint16, B uint8) bool {
  1075		// If the threshold is too low, we do extraneous work.
  1076		// If the threshold is too high, maps that grow and shrink can hold on to lots of unused memory.
  1077		// "too many" means (approximately) as many overflow buckets as regular buckets.
  1078		// See incrnoverflow for more details.
  1079		if B > 15 {
  1080			B = 15
  1081		}
  1082		// The compiler doesn't see here that B < 16; mask B to generate shorter shift code.
  1083		return noverflow >= uint16(1)<<(B&15)
  1084	}
  1085	
  1086	// growing reports whether h is growing. The growth may be to the same size or bigger.
  1087	func (h *hmap) growing() bool {
  1088		return h.oldbuckets != nil
  1089	}
  1090	
  1091	// sameSizeGrow reports whether the current growth is to a map of the same size.
  1092	func (h *hmap) sameSizeGrow() bool {
  1093		return h.flags&sameSizeGrow != 0
  1094	}
  1095	
  1096	// noldbuckets calculates the number of buckets prior to the current map growth.
  1097	func (h *hmap) noldbuckets() uintptr {
  1098		oldB := h.B
  1099		if !h.sameSizeGrow() {
  1100			oldB--
  1101		}
  1102		return bucketShift(oldB)
  1103	}
  1104	
  1105	// oldbucketmask provides a mask that can be applied to calculate n % noldbuckets().
  1106	func (h *hmap) oldbucketmask() uintptr {
  1107		return h.noldbuckets() - 1
  1108	}
  1109	
  1110	func growWork(t *maptype, h *hmap, bucket uintptr) {
  1111		// make sure we evacuate the oldbucket corresponding
  1112		// to the bucket we're about to use
  1113		evacuate(t, h, bucket&h.oldbucketmask())
  1114	
  1115		// evacuate one more oldbucket to make progress on growing
  1116		if h.growing() {
  1117			evacuate(t, h, h.nevacuate)
  1118		}
  1119	}
  1120	
  1121	func bucketEvacuated(t *maptype, h *hmap, bucket uintptr) bool {
  1122		b := (*bmap)(add(h.oldbuckets, bucket*uintptr(t.bucketsize)))
  1123		return evacuated(b)
  1124	}
  1125	
  1126	// evacDst is an evacuation destination.
  1127	type evacDst struct {
  1128		b *bmap          // current destination bucket
  1129		i int            // key/elem index into b
  1130		k unsafe.Pointer // pointer to current key storage
  1131		e unsafe.Pointer // pointer to current elem storage
  1132	}
  1133	
  1134	func evacuate(t *maptype, h *hmap, oldbucket uintptr) {
  1135		b := (*bmap)(add(h.oldbuckets, oldbucket*uintptr(t.bucketsize)))
  1136		newbit := h.noldbuckets()
  1137		if !evacuated(b) {
  1138			// TODO: reuse overflow buckets instead of using new ones, if there
  1139			// is no iterator using the old buckets.  (If !oldIterator.)
  1140	
  1141			// xy contains the x and y (low and high) evacuation destinations.
  1142			var xy [2]evacDst
  1143			x := &xy[0]
  1144			x.b = (*bmap)(add(h.buckets, oldbucket*uintptr(t.bucketsize)))
  1145			x.k = add(unsafe.Pointer(x.b), dataOffset)
  1146			x.e = add(x.k, bucketCnt*uintptr(t.keysize))
  1147	
  1148			if !h.sameSizeGrow() {
  1149				// Only calculate y pointers if we're growing bigger.
  1150				// Otherwise GC can see bad pointers.
  1151				y := &xy[1]
  1152				y.b = (*bmap)(add(h.buckets, (oldbucket+newbit)*uintptr(t.bucketsize)))
  1153				y.k = add(unsafe.Pointer(y.b), dataOffset)
  1154				y.e = add(y.k, bucketCnt*uintptr(t.keysize))
  1155			}
  1156	
  1157			for ; b != nil; b = b.overflow(t) {
  1158				k := add(unsafe.Pointer(b), dataOffset)
  1159				e := add(k, bucketCnt*uintptr(t.keysize))
  1160				for i := 0; i < bucketCnt; i, k, e = i+1, add(k, uintptr(t.keysize)), add(e, uintptr(t.elemsize)) {
  1161					top := b.tophash[i]
  1162					if isEmpty(top) {
  1163						b.tophash[i] = evacuatedEmpty
  1164						continue
  1165					}
  1166					if top < minTopHash {
  1167						throw("bad map state")
  1168					}
  1169					k2 := k
  1170					if t.indirectkey() {
  1171						k2 = *((*unsafe.Pointer)(k2))
  1172					}
  1173					var useY uint8
  1174					if !h.sameSizeGrow() {
  1175						// Compute hash to make our evacuation decision (whether we need
  1176						// to send this key/elem to bucket x or bucket y).
  1177						hash := t.key.alg.hash(k2, uintptr(h.hash0))
  1178						if h.flags&iterator != 0 && !t.reflexivekey() && !t.key.alg.equal(k2, k2) {
  1179							// If key != key (NaNs), then the hash could be (and probably
  1180							// will be) entirely different from the old hash. Moreover,
  1181							// it isn't reproducible. Reproducibility is required in the
  1182							// presence of iterators, as our evacuation decision must
  1183							// match whatever decision the iterator made.
  1184							// Fortunately, we have the freedom to send these keys either
  1185							// way. Also, tophash is meaningless for these kinds of keys.
  1186							// We let the low bit of tophash drive the evacuation decision.
  1187							// We recompute a new random tophash for the next level so
  1188							// these keys will get evenly distributed across all buckets
  1189							// after multiple grows.
  1190							useY = top & 1
  1191							top = tophash(hash)
  1192						} else {
  1193							if hash&newbit != 0 {
  1194								useY = 1
  1195							}
  1196						}
  1197					}
  1198	
  1199					if evacuatedX+1 != evacuatedY || evacuatedX^1 != evacuatedY {
  1200						throw("bad evacuatedN")
  1201					}
  1202	
  1203					b.tophash[i] = evacuatedX + useY // evacuatedX + 1 == evacuatedY
  1204					dst := &xy[useY]                 // evacuation destination
  1205	
  1206					if dst.i == bucketCnt {
  1207						dst.b = h.newoverflow(t, dst.b)
  1208						dst.i = 0
  1209						dst.k = add(unsafe.Pointer(dst.b), dataOffset)
  1210						dst.e = add(dst.k, bucketCnt*uintptr(t.keysize))
  1211					}
  1212					dst.b.tophash[dst.i&(bucketCnt-1)] = top // mask dst.i as an optimization, to avoid a bounds check
  1213					if t.indirectkey() {
  1214						*(*unsafe.Pointer)(dst.k) = k2 // copy pointer
  1215					} else {
  1216						typedmemmove(t.key, dst.k, k) // copy elem
  1217					}
  1218					if t.indirectelem() {
  1219						*(*unsafe.Pointer)(dst.e) = *(*unsafe.Pointer)(e)
  1220					} else {
  1221						typedmemmove(t.elem, dst.e, e)
  1222					}
  1223					dst.i++
  1224					// These updates might push these pointers past the end of the
  1225					// key or elem arrays.  That's ok, as we have the overflow pointer
  1226					// at the end of the bucket to protect against pointing past the
  1227					// end of the bucket.
  1228					dst.k = add(dst.k, uintptr(t.keysize))
  1229					dst.e = add(dst.e, uintptr(t.elemsize))
  1230				}
  1231			}
  1232			// Unlink the overflow buckets & clear key/elem to help GC.
  1233			if h.flags&oldIterator == 0 && t.bucket.ptrdata != 0 {
  1234				b := add(h.oldbuckets, oldbucket*uintptr(t.bucketsize))
  1235				// Preserve b.tophash because the evacuation
  1236				// state is maintained there.
  1237				ptr := add(b, dataOffset)
  1238				n := uintptr(t.bucketsize) - dataOffset
  1239				memclrHasPointers(ptr, n)
  1240			}
  1241		}
  1242	
  1243		if oldbucket == h.nevacuate {
  1244			advanceEvacuationMark(h, t, newbit)
  1245		}
  1246	}
  1247	
  1248	func advanceEvacuationMark(h *hmap, t *maptype, newbit uintptr) {
  1249		h.nevacuate++
  1250		// Experiments suggest that 1024 is overkill by at least an order of magnitude.
  1251		// Put it in there as a safeguard anyway, to ensure O(1) behavior.
  1252		stop := h.nevacuate + 1024
  1253		if stop > newbit {
  1254			stop = newbit
  1255		}
  1256		for h.nevacuate != stop && bucketEvacuated(t, h, h.nevacuate) {
  1257			h.nevacuate++
  1258		}
  1259		if h.nevacuate == newbit { // newbit == # of oldbuckets
  1260			// Growing is all done. Free old main bucket array.
  1261			h.oldbuckets = nil
  1262			// Can discard old overflow buckets as well.
  1263			// If they are still referenced by an iterator,
  1264			// then the iterator holds a pointers to the slice.
  1265			if h.extra != nil {
  1266				h.extra.oldoverflow = nil
  1267			}
  1268			h.flags &^= sameSizeGrow
  1269		}
  1270	}
  1271	
  1272	func ismapkey(t *_type) bool {
  1273		return t.alg.hash != nil
  1274	}
  1275	
  1276	// Reflect stubs. Called from ../reflect/asm_*.s
  1277	
  1278	//go:linkname reflect_makemap reflect.makemap
  1279	func reflect_makemap(t *maptype, cap int) *hmap {
  1280		// Check invariants and reflects math.
  1281		if !ismapkey(t.key) {
  1282			throw("runtime.reflect_makemap: unsupported map key type")
  1283		}
  1284		if t.key.size > maxKeySize && (!t.indirectkey() || t.keysize != uint8(sys.PtrSize)) ||
  1285			t.key.size <= maxKeySize && (t.indirectkey() || t.keysize != uint8(t.key.size)) {
  1286			throw("key size wrong")
  1287		}
  1288		if t.elem.size > maxElemSize && (!t.indirectelem() || t.elemsize != uint8(sys.PtrSize)) ||
  1289			t.elem.size <= maxElemSize && (t.indirectelem() || t.elemsize != uint8(t.elem.size)) {
  1290			throw("elem size wrong")
  1291		}
  1292		if t.key.align > bucketCnt {
  1293			throw("key align too big")
  1294		}
  1295		if t.elem.align > bucketCnt {
  1296			throw("elem align too big")
  1297		}
  1298		if t.key.size%uintptr(t.key.align) != 0 {
  1299			throw("key size not a multiple of key align")
  1300		}
  1301		if t.elem.size%uintptr(t.elem.align) != 0 {
  1302			throw("elem size not a multiple of elem align")
  1303		}
  1304		if bucketCnt < 8 {
  1305			throw("bucketsize too small for proper alignment")
  1306		}
  1307		if dataOffset%uintptr(t.key.align) != 0 {
  1308			throw("need padding in bucket (key)")
  1309		}
  1310		if dataOffset%uintptr(t.elem.align) != 0 {
  1311			throw("need padding in bucket (elem)")
  1312		}
  1313	
  1314		return makemap(t, cap, nil)
  1315	}
  1316	
  1317	//go:linkname reflect_mapaccess reflect.mapaccess
  1318	func reflect_mapaccess(t *maptype, h *hmap, key unsafe.Pointer) unsafe.Pointer {
  1319		elem, ok := mapaccess2(t, h, key)
  1320		if !ok {
  1321			// reflect wants nil for a missing element
  1322			elem = nil
  1323		}
  1324		return elem
  1325	}
  1326	
  1327	//go:linkname reflect_mapassign reflect.mapassign
  1328	func reflect_mapassign(t *maptype, h *hmap, key unsafe.Pointer, elem unsafe.Pointer) {
  1329		p := mapassign(t, h, key)
  1330		typedmemmove(t.elem, p, elem)
  1331	}
  1332	
  1333	//go:linkname reflect_mapdelete reflect.mapdelete
  1334	func reflect_mapdelete(t *maptype, h *hmap, key unsafe.Pointer) {
  1335		mapdelete(t, h, key)
  1336	}
  1337	
  1338	//go:linkname reflect_mapiterinit reflect.mapiterinit
  1339	func reflect_mapiterinit(t *maptype, h *hmap) *hiter {
  1340		it := new(hiter)
  1341		mapiterinit(t, h, it)
  1342		return it
  1343	}
  1344	
  1345	//go:linkname reflect_mapiternext reflect.mapiternext
  1346	func reflect_mapiternext(it *hiter) {
  1347		mapiternext(it)
  1348	}
  1349	
  1350	//go:linkname reflect_mapiterkey reflect.mapiterkey
  1351	func reflect_mapiterkey(it *hiter) unsafe.Pointer {
  1352		return it.key
  1353	}
  1354	
  1355	//go:linkname reflect_mapiterelem reflect.mapiterelem
  1356	func reflect_mapiterelem(it *hiter) unsafe.Pointer {
  1357		return it.elem
  1358	}
  1359	
  1360	//go:linkname reflect_maplen reflect.maplen
  1361	func reflect_maplen(h *hmap) int {
  1362		if h == nil {
  1363			return 0
  1364		}
  1365		if raceenabled {
  1366			callerpc := getcallerpc()
  1367			racereadpc(unsafe.Pointer(h), callerpc, funcPC(reflect_maplen))
  1368		}
  1369		return h.count
  1370	}
  1371	
  1372	//go:linkname reflectlite_maplen internal/reflectlite.maplen
  1373	func reflectlite_maplen(h *hmap) int {
  1374		if h == nil {
  1375			return 0
  1376		}
  1377		if raceenabled {
  1378			callerpc := getcallerpc()
  1379			racereadpc(unsafe.Pointer(h), callerpc, funcPC(reflect_maplen))
  1380		}
  1381		return h.count
  1382	}
  1383	
  1384	//go:linkname reflect_ismapkey reflect.ismapkey
  1385	func reflect_ismapkey(t *_type) bool {
  1386		return ismapkey(t)
  1387	}
  1388	
  1389	const maxZero = 1024 // must match value in cmd/compile/internal/gc/walk.go
  1390	var zeroVal [maxZero]byte
  1391	

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