a171ac0380
Libgo's implementation of math.Ldexp declared the libc "ldexp" as
taking an 'int' exponent argument, which is not quite right for 64-bit
platforms (exp arg is always int32); this could yield incorrect
results for exponent values outside the range of Minint32/Maxint32.
Fix by upating the type for the libc version of ldexp, and adding
guards to screen for out-of-range exponents.
Fixes #21323.
Reviewed-on: https://go-review.googlesource.com/54250
From-SVN: r250992
58 lines
1.2 KiB
Go
58 lines
1.2 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, int32) float64
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func Ldexp(frac float64, exp int) float64 {
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if exp > MaxInt32 {
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exp = MaxInt32
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} else if exp < MinInt32 {
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exp = MinInt32
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}
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r := libc_ldexp(frac, int32(exp))
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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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