Source file src/pkg/math/rand/gen_cooked.go

     1	// Copyright 2009 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	// +build ignore
     6	
     7	// This program computes the value of rng_cooked in rng.go,
     8	// which is used for seeding all instances of rand.Source.
     9	// a 64bit and a 63bit version of the array is printed to
    10	// the standard output.
    11	
    12	package main
    13	
    14	import "fmt"
    15	
    16	const (
    17		length = 607
    18		tap    = 273
    19		mask   = (1 << 63) - 1
    20		a      = 48271
    21		m      = (1 << 31) - 1
    22		q      = 44488
    23		r      = 3399
    24	)
    25	
    26	var (
    27		rngVec          [length]int64
    28		rngTap, rngFeed int
    29	)
    30	
    31	func seedrand(x int32) int32 {
    32		hi := x / q
    33		lo := x % q
    34		x = a*lo - r*hi
    35		if x < 0 {
    36			x += m
    37		}
    38		return x
    39	}
    40	
    41	func srand(seed int32) {
    42		rngTap = 0
    43		rngFeed = length - tap
    44		seed %= m
    45		if seed < 0 {
    46			seed += m
    47		} else if seed == 0 {
    48			seed = 89482311
    49		}
    50		x := seed
    51		for i := -20; i < length; i++ {
    52			x = seedrand(x)
    53			if i >= 0 {
    54				var u int64
    55				u = int64(x) << 20
    56				x = seedrand(x)
    57				u ^= int64(x) << 10
    58				x = seedrand(x)
    59				u ^= int64(x)
    60				rngVec[i] = u
    61			}
    62		}
    63	}
    64	
    65	func vrand() int64 {
    66		rngTap--
    67		if rngTap < 0 {
    68			rngTap += length
    69		}
    70		rngFeed--
    71		if rngFeed < 0 {
    72			rngFeed += length
    73		}
    74		x := (rngVec[rngFeed] + rngVec[rngTap])
    75		rngVec[rngFeed] = x
    76		return x
    77	}
    78	
    79	func main() {
    80		srand(1)
    81		for i := uint64(0); i < 7.8e12; i++ {
    82			vrand()
    83		}
    84		fmt.Printf("rngVec after 7.8e12 calls to vrand:\n%#v\n", rngVec)
    85		for i := range rngVec {
    86			rngVec[i] &= mask
    87		}
    88		fmt.Printf("lower 63bit of rngVec after 7.8e12 calls to vrand:\n%#v\n", rngVec)
    89	}
    90	

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