KDOC 442: メモリエイリアシング検出と対策の例を見る

 // SetFrac sets z to a/b and returns z.
 func (z *Rat) SetFrac(a, b *Int) *Rat {
-       z.a.Set(a)
        z.a.neg = a.neg != b.neg
-       z.b = z.b.set(b.abs)
+       babs := b.abs
+       if &z.a == b || alias(z.a.abs, babs) {
+               babs = nat(nil).set(babs) // make a copy
+       }
+       z.a.abs = z.a.abs.set(a.abs)
+       z.b = z.b.set(babs)
        return z.norm()
 }