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math/big: use internal square for Rat

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updates #13745

A squared rational is always positive and can not
be reduced since the numerator and denominator had
no previous common factors.  The nat multiplication
can be performed using the internal sqr method.

Change-Id: I558f5b38e379bfd26ff163c9489006d7e5a9cfaa
Reviewed-on: https://go-review.googlesource.com/56776
Reviewed-by: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Brian Kessler 2017-08-17 23:44:34 -07:00 committed by Robert Griesemer
parent 66a1d37bf7
commit fe08ebaebb
1 changed files with 7 additions and 0 deletions
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7
src/math/big/rat.go
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@ -490,6 +490,13 @@ func (z *Rat) Sub(x, y *Rat) *Rat {
// Mul sets z to the product x*y and returns z.
func (z *Rat) Mul(x, y *Rat) *Rat {
if x == y {
// a squared Rat is positive and can't be reduced
z.a.neg = false
z.a.abs = z.a.abs.sqr(x.a.abs)
z.b.abs = z.b.abs.sqr(x.b.abs)
return z
}
z.a.Mul(&x.a, &y.a)
z.b.abs = mulDenom(z.b.abs, x.b.abs, y.b.abs)
return z.norm()