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 if haveArchRemainder { 39 return archRemainder(x, y) 40 } 41 return remainder(x, y) 42 } 43 44 func remainder(x, y float64) float64 { 45 const ( 46 Tiny = 4.45014771701440276618e-308 // 0x0020000000000000 47 HalfMax = MaxFloat64 / 2 48 ) 49 // special cases 50 switch { 51 case IsNaN(x) || IsNaN(y) || IsInf(x, 0) || y == 0: 52 return NaN() 53 case IsInf(y, 0): 54 return x 55 } 56 sign := false 57 if x < 0 { 58 x = -x 59 sign = true 60 } 61 if y < 0 { 62 y = -y 63 } 64 if x == y { 65 if sign { 66 zero := 0.0 67 return -zero 68 } 69 return 0 70 } 71 if y <= HalfMax { 72 x = Mod(x, y+y) // now x < 2y 73 } 74 if y < Tiny { 75 if x+x > y { 76 x -= y 77 if x+x >= y { 78 x -= y 79 } 80 } 81 } else { 82 yHalf := 0.5 * y 83 if x > yHalf { 84 x -= y 85 if x >= yHalf { 86 x -= y 87 } 88 } 89 } 90 if sign { 91 x = -x 92 } 93 return x 94 } 95