From 1927a869d4917cb7bf47cc069dde574e01c26de3 Mon Sep 17 00:00:00 2001 From: Peter Reid Date: Fri, 4 Sep 2015 22:10:39 -0400 Subject: [PATCH 1/2] Fix for issue #28012: pow overflow inconsistency Overflows in integer pow() computations would be missed if they preceded a 0 bit of the exponent being processed. This made calls such as 2i32.pow(1024) not trigger an overflow. --- src/libcore/num/mod.rs | 26 +++++++++++--------------- 1 file changed, 11 insertions(+), 15 deletions(-) diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs index 05c7e8b8de4..127f8d3b5a2 100644 --- a/src/libcore/num/mod.rs +++ b/src/libcore/num/mod.rs @@ -537,25 +537,21 @@ macro_rules! int_impl { let mut base = self; let mut acc = Self::one(); - 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 } From a593a211fe71e82b3f87dd16fb25831fb8a00442 Mon Sep 17 00:00:00 2001 From: Peter Reid Date: Sun, 13 Sep 2015 22:19:36 -0400 Subject: [PATCH 2/2] Add test for overflowing pow This would catch regressions of issue #28012. --- src/test/run-fail/overflowing-pow.rs | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) create mode 100644 src/test/run-fail/overflowing-pow.rs diff --git a/src/test/run-fail/overflowing-pow.rs b/src/test/run-fail/overflowing-pow.rs new file mode 100644 index 00000000000..15335b8dfb1 --- /dev/null +++ b/src/test/run-fail/overflowing-pow.rs @@ -0,0 +1,16 @@ +// Copyright 2015 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +// error-pattern:thread '
' panicked at 'arithmetic operation overflowed' +// compile-flags: -C debug-assertions + +fn main() { + let _x = 2i32.pow(1024); +}