From 9926b33276cb3a349952d8d47a5d8b17bbb3cbdf Mon Sep 17 00:00:00 2001 From: Caleb Jones Date: Wed, 20 Jul 2016 18:23:52 -0400 Subject: Fix overflow checking in unsigned pow() The pow() method for unsigned integers produced 0 instead of trapping overflow for certain inputs. Calls such as 2u32.pow(1024) produced 0 when they should trap an overflow. This also adds tests for the correctly handling overflow in unsigned pow(). For issue number #34913 --- src/libcore/num/mod.rs | 26 +++++++++++--------------- 1 file changed, 11 insertions(+), 15 deletions(-) (limited to 'src/libcore') diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs index 4636811aa46..1032826a093 100644 --- a/src/libcore/num/mod.rs +++ b/src/libcore/num/mod.rs @@ -2217,25 +2217,21 @@ macro_rules! uint_impl { let mut base = self; let mut acc = 1; - let mut prev_base = self; - let mut base_oflo = false; - while exp > 0 { + while exp > 1 { if (exp & 1) == 1 { - if base_oflo { - // ensure overflow occurs in the same manner it - // would have otherwise (i.e. signal any exception - // it would have otherwise). - acc = acc * (prev_base * prev_base); - } else { - acc = acc * base; - } + acc = acc * base; } - prev_base = base; - let (new_base, new_base_oflo) = base.overflowing_mul(base); - base = new_base; - base_oflo = new_base_oflo; exp /= 2; + base = base * base; } + + // Deal with the final bit of the exponent separately, since + // squaring the base afterwards is not necessary and may cause a + // needless overflow. + if exp == 1 { + acc = acc * base; + } + acc } -- cgit 1.4.1-3-g733a5