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math/big: fix aliasing bug in Float.Quo

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TBR r, adonovan

Change-Id: I1a38e2d724bf1147c7307a7e5ae855c42c60428c
Reviewed-on: https://go-review.googlesource.com/4875
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Robert Griesemer 2015-02-13 20:15:40 -08:00
parent a809dc7adb
commit b7bfb54eaa
1 changed files with 5 additions and 1 deletions
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6
src/math/big/float.go
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@ -967,12 +967,16 @@ func (z *Float) uquo(x, y *Float) {
// to shorten x for faster division. But we must be extra careful
// with rounding in that case.
// Compute d before division since there may be aliasing of x.mant
// (via xadj) or y.mant with z.mant.
d := len(xadj) - len(y.mant)
// divide
var r nat
z.mant, r = z.mant.div(nil, xadj, y.mant)
// determine exponent
e := int64(x.exp) - int64(y.exp) - int64(len(xadj)-len(y.mant)-len(z.mant))*_W
e := int64(x.exp) - int64(y.exp) - int64(d-len(z.mant))*_W
// normalize mantissa
z.setExp(e - int64(fnorm(z.mant)))