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// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package math
// The original C code and the comment below are from
// FreeBSD's /usr/src/lib/msun/src/e_remainder.c and came
// with this notice. The go code is a simplified version of
// the original C.
//
// ====================================================
// Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
//
// Developed at SunPro, a Sun Microsystems, Inc. business.
// Permission to use, copy, modify, and distribute this
// software is freely granted, provided that this notice
// is preserved.
// ====================================================
//
// __ieee754_remainder(x,y)
// Return :
// returns x REM y = x - [x/y]*y as if in infinite
// precision arithmetic, where [x/y] is the (infinite bit)
// integer nearest x/y (in half way cases, choose the even one).
// Method :
// Based on Mod() returning x - [x/y]chopped * y exactly.
// Remainder returns the IEEE 754 floating-point remainder of x/y.
//
// Special cases are:
//
// Remainder(±Inf, y) = NaN
// Remainder(NaN, y) = NaN
// Remainder(x, 0) = NaN
// Remainder(x, ±Inf) = x
// Remainder(x, NaN) = NaN
func Remainder(x, y float64) float64 {
if haveArchRemainder {
return archRemainder(x, y)
}
return remainder(x, y)
}
func remainder(x, y float64) float64 {
const (
Tiny = 4.45014771701440276618e-308 // 0x0020000000000000
HalfMax = MaxFloat64 / 2
)
// special cases
switch {
case IsNaN(x) || IsNaN(y) || IsInf(x, 0) || y == 0:
return NaN()
case IsInf(y, 0):
return x
}
sign := false
if x < 0 {
x = -x
sign = true
}
if y < 0 {
y = -y
}
if x == y {
if sign {
zero := 0.0
return -zero
}
return 0
}
if y <= HalfMax {
x = Mod(x, y+y) // now x < 2y
}
if y < Tiny {
if x+x > y {
x -= y
if x+x >= y {
x -= y
}
}
} else {
yHalf := 0.5 * y
if x > yHalf {
x -= y
if x >= yHalf {
x -= y
}
}
}
if sign {
x = -x
}
return x
}
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