1 // Copyright 2010 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 math 6 7 // The original C code and the comment below are from 8 // FreeBSD's /usr/src/lib/msun/src/e_remainder.c and came 9 // with this notice. The go code is a simplified version of 10 // the original C. 11 // 12 // ==================================================== 13 // Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 14 // 15 // Developed at SunPro, a Sun Microsystems, Inc. business. 16 // Permission to use, copy, modify, and distribute this 17 // software is freely granted, provided that this notice 18 // is preserved. 19 // ==================================================== 20 // 21 // __ieee754_remainder(x,y) 22 // Return : 23 // returns x REM y = x - [x/y]*y as if in infinite 24 // precision arithmetic, where [x/y] is the (infinite bit) 25 // integer nearest x/y (in half way cases, choose the even one). 26 // Method : 27 // Based on Mod() returning x - [x/y]chopped * y exactly. 28 29 // Remainder returns the IEEE 754 floating-point remainder of x/y. 30 // 31 // Special cases are: 32 // Remainder(±Inf, y) = NaN 33 // Remainder(NaN, y) = NaN 34 // Remainder(x, 0) = NaN 35 // Remainder(x, ±Inf) = x 36 // Remainder(x, NaN) = NaN 37 func Remainder(x, y float64) float64 38 39 func remainder(x, y float64) float64 { 40 const ( 41 Tiny = 4.45014771701440276618e-308 // 0x0020000000000000 42 HalfMax = MaxFloat64 / 2 43 ) 44 // special cases 45 switch { 46 case IsNaN(x) || IsNaN(y) || IsInf(x, 0) || y == 0: 47 return NaN() 48 case IsInf(y, 0): 49 return x 50 } 51 sign := false 52 if x < 0 { 53 x = -x 54 sign = true 55 } 56 if y < 0 { 57 y = -y 58 } 59 if x == y { 60 if sign { 61 zero := 0.0 62 return -zero 63 } 64 return 0 65 } 66 if y <= HalfMax { 67 x = Mod(x, y+y) // now x < 2y 68 } 69 if y < Tiny { 70 if x+x > y { 71 x -= y 72 if x+x >= y { 73 x -= y 74 } 75 } 76 } else { 77 yHalf := 0.5 * y 78 if x > yHalf { 79 x -= y 80 if x >= yHalf { 81 x -= y 82 } 83 } 84 } 85 if sign { 86 x = -x 87 } 88 return x 89 } 90