From 9926b33276cb3a349952d8d47a5d8b17bbb3cbdf Mon Sep 17 00:00:00 2001 From: Caleb Jones Date: Wed, 20 Jul 2016 18:23:52 -0400 Subject: [PATCH 1/2] 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 ++++++++----------- ...owing-pow.rs => overflowing-pow-signed.rs} | 0 src/test/run-fail/overflowing-pow-unsigned.rs | 16 ++++++++++++ 3 files changed, 27 insertions(+), 15 deletions(-) rename src/test/run-fail/{overflowing-pow.rs => overflowing-pow-signed.rs} (100%) create mode 100644 src/test/run-fail/overflowing-pow-unsigned.rs diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs index 4636811aa46da..1032826a09353 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 } diff --git a/src/test/run-fail/overflowing-pow.rs b/src/test/run-fail/overflowing-pow-signed.rs similarity index 100% rename from src/test/run-fail/overflowing-pow.rs rename to src/test/run-fail/overflowing-pow-signed.rs diff --git a/src/test/run-fail/overflowing-pow-unsigned.rs b/src/test/run-fail/overflowing-pow-unsigned.rs new file mode 100644 index 0000000000000..5dca7795462eb --- /dev/null +++ b/src/test/run-fail/overflowing-pow-unsigned.rs @@ -0,0 +1,16 @@ +// Copyright 2016 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 'main' panicked at 'attempted to multiply with overflow' +// compile-flags: -C debug-assertions + +fn main() { + let _x = 2u32.pow(1024); +} From b8c4e9c235db5f67129abdae8f336e06bf2bc8ba Mon Sep 17 00:00:00 2001 From: Caleb Jones Date: Sat, 6 Aug 2016 23:58:16 -0400 Subject: [PATCH 2/2] Change the expected panic message for unsigned --- src/test/run-fail/overflowing-pow-unsigned.rs | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/test/run-fail/overflowing-pow-unsigned.rs b/src/test/run-fail/overflowing-pow-unsigned.rs index 5dca7795462eb..d3e7035279fbe 100644 --- a/src/test/run-fail/overflowing-pow-unsigned.rs +++ b/src/test/run-fail/overflowing-pow-unsigned.rs @@ -8,7 +8,7 @@ // option. This file may not be copied, modified, or distributed // except according to those terms. -// error-pattern:thread 'main' panicked at 'attempted to multiply with overflow' +// error-pattern:thread 'main' panicked at 'attempt to multiply with overflow' // compile-flags: -C debug-assertions fn main() {