Auto merge of #28248 - PeterReid:master, r=alexcrichton
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. Fixes #28012
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commit
9da7706dd6
2 changed files with 27 additions and 15 deletions
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@ -537,25 +537,21 @@ macro_rules! int_impl {
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let mut base = self;
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let mut acc = Self::one();
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let mut prev_base = self;
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let mut base_oflo = false;
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while exp > 0 {
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while exp > 1 {
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if (exp & 1) == 1 {
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if base_oflo {
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// ensure overflow occurs in the same manner it
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// would have otherwise (i.e. signal any exception
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// it would have otherwise).
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acc = acc * (prev_base * prev_base);
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} else {
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acc = acc * base;
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}
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acc = acc * base;
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}
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prev_base = base;
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let (new_base, new_base_oflo) = base.overflowing_mul(base);
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base = new_base;
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base_oflo = new_base_oflo;
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exp /= 2;
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base = base * base;
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}
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// Deal with the final bit of the exponent separately, since
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// squaring the base afterwards is not necessary and may cause a
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// needless overflow.
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if exp == 1 {
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acc = acc * base;
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}
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acc
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}
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16
src/test/run-fail/overflowing-pow.rs
Normal file
16
src/test/run-fail/overflowing-pow.rs
Normal file
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@ -0,0 +1,16 @@
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// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// error-pattern:thread '<main>' panicked at 'arithmetic operation overflowed'
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// compile-flags: -C debug-assertions
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fn main() {
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let _x = 2i32.pow(1024);
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}
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