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big: bug fix for Quo aliasing problem
Fixes #820. R=rsc CC=golang-dev https://golang.org/cl/1453041
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@ -160,9 +160,11 @@ func (z *Rat) Quo(x, y *Rat) *Rat {
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if len(y.a.abs) == 0 {
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panic("division by zero")
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}
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z.a.abs = z.a.abs.mul(x.a.abs, y.b)
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z.b = z.b.mul(x.b, y.a.abs)
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z.a.neg = x.a.neg != y.a.neg
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a := mulNat(&x.a, y.b)
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b := mulNat(&y.a, x.b)
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z.a.abs = a.abs
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z.b = b.abs
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z.a.neg = a.neg != b.neg
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return z.norm()
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}
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@ -175,3 +175,29 @@ func TestRatBin(t *testing.T) {
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}
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}
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}
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func TestIssue820(t *testing.T) {
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x := NewRat(3, 1)
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y := NewRat(2, 1)
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z := y.Quo(x, y)
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q := NewRat(3, 2)
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if z.Cmp(q) != 0 {
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t.Errorf("got %s want %s", z, q)
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}
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y = NewRat(3, 1)
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x = NewRat(2, 1)
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z = y.Quo(x, y)
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q = NewRat(2, 3)
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if z.Cmp(q) != 0 {
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t.Errorf("got %s want %s", z, q)
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}
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x = NewRat(3, 1)
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z = x.Quo(x, x)
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q = NewRat(3, 3)
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if z.Cmp(q) != 0 {
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t.Errorf("got %s want %s", z, q)
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}
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}
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