6c88c77ec7
PR go/52358 math: Work around bug in Solaris 9 implementation of ldexp. The bug is that ldexp(-1, -1075) should return -0, but the Solaris 9 implementation returns +0. From-SVN: r186913
62 lines
1.5 KiB
Go
62 lines
1.5 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package math
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// Ldexp is the inverse of Frexp.
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// It returns frac × 2**exp.
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//
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// Special cases are:
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// Ldexp(±0, exp) = ±0
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// Ldexp(±Inf, exp) = ±Inf
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// Ldexp(NaN, exp) = NaN
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//extern ldexp
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func libc_ldexp(float64, int) float64
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func Ldexp(frac float64, exp int) float64 {
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r := libc_ldexp(frac, exp)
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// Work around a bug in the implementation of ldexp on Solaris
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// 9. If multiplying a negative number by 2 raised to a
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// negative exponent underflows, we want to return negative
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// zero, but the Solaris 9 implementation returns positive
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// zero. This workaround can be removed when and if we no
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// longer care about Solaris 9.
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if r == 0 && frac < 0 && exp < 0 {
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r = Copysign(0, frac)
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}
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return r
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}
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func ldexp(frac float64, exp int) float64 {
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// special cases
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switch {
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case frac == 0:
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return frac // correctly return -0
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case IsInf(frac, 0) || IsNaN(frac):
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return frac
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}
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frac, e := normalize(frac)
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exp += e
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x := Float64bits(frac)
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exp += int(x>>shift)&mask - bias
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if exp < -1074 {
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return Copysign(0, frac) // underflow
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}
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if exp > 1023 { // overflow
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if frac < 0 {
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return Inf(-1)
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}
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return Inf(1)
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}
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var m float64 = 1
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if exp < -1022 { // denormal
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exp += 52
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m = 1.0 / (1 << 52) // 2**-52
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}
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x &^= mask << shift
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x |= uint64(exp+bias) << shift
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return m * Float64frombits(x)
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}
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