From: Robert Griesemer <gri@golang.org>
Date: Sat, 14 Feb 2015 04:15:40 +0000 (-0800)
Subject: math/big: fix aliasing bug in Float.Quo
X-Git-Tag: go1.5beta1~1990
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=b7bfb54eaa84a7de187df905ae8f74c8fed515f4;p=gostls13.git

math/big: fix aliasing bug in Float.Quo

TBR r, adonovan

Change-Id: I1a38e2d724bf1147c7307a7e5ae855c42c60428c
Reviewed-on: https://go-review.googlesource.com/4875
Reviewed-by: Robert Griesemer <gri@golang.org>
---

diff --git a/src/math/big/float.go b/src/math/big/float.go
index dd6700137b..314fd689ed 100644
--- a/src/math/big/float.go
+++ b/src/math/big/float.go
@@ -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)))