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 5package 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 37func Remainder(x, y float64) float64 { 38 return remainder(x, y) 39} 40 41func remainder(x, y float64) float64 { 42 const ( 43 Tiny = 4.45014771701440276618e-308 // 0x0020000000000000 44 HalfMax = MaxFloat64 / 2 45 ) 46 // special cases 47 switch { 48 case IsNaN(x) || IsNaN(y) || IsInf(x, 0) || y == 0: 49 return NaN() 50 case IsInf(y, 0): 51 return x 52 } 53 sign := false 54 if x < 0 { 55 x = -x 56 sign = true 57 } 58 if y < 0 { 59 y = -y 60 } 61 if x == y { 62 return 0 63 } 64 if y <= HalfMax { 65 x = Mod(x, y+y) // now x < 2y 66 } 67 if y < Tiny { 68 if x+x > y { 69 x -= y 70 if x+x >= y { 71 x -= y 72 } 73 } 74 } else { 75 yHalf := 0.5 * y 76 if x > yHalf { 77 x -= y 78 if x >= yHalf { 79 x -= y 80 } 81 } 82 } 83 if sign { 84 x = -x 85 } 86 return x 87} 88