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Auto merge of #25527 - inrustwetrust:const-not-overflow, r=alexcrichton

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Fixes #23968.
Since the values are stored in a u64 internally, we need to be mask away the
high bits after applying the ! operator. Otherwise, these bits will be set to
one, causing overflow.
This commit is contained in:
bors 2015-05-17 23:53:41 +00:00
commit 0cc99f9cc9
2 changed files with 34 additions and 3 deletions
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16
src/librustc/middle/const_eval.rs
View File

@ -1,4 +1,4 @@
// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
// Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
@ -34,7 +34,7 @@ use std::borrow::{Cow, IntoCow};
use std::num::wrapping::OverflowingOps;
use std::cmp::Ordering;
use std::collections::hash_map::Entry::Vacant;
use std::{i8, i16, i32, i64};
use std::{i8, i16, i32, i64, u8, u16, u32, u64};
use std::rc::Rc;
fn lookup_const<'a>(tcx: &'a ty::ctxt, e: &Expr) -> Option<&'a Expr> {
@ -461,6 +461,16 @@ pub fn const_uint_checked_neg<'a>(
Ok(const_uint((!a).wrapping_add(1)))
}
fn const_uint_not(a: u64, opt_ety: Option<UintTy>) -> const_val {
let mask = match opt_ety {
Some(UintTy::U8) => u8::MAX as u64,
Some(UintTy::U16) => u16::MAX as u64,
Some(UintTy::U32) => u32::MAX as u64,
None | Some(UintTy::U64) => u64::MAX,
};
const_uint(!a & mask)
}
macro_rules! overflow_checking_body {
($a:ident, $b:ident, $ety:ident, $overflowing_op:ident,
lhs: $to_8_lhs:ident $to_16_lhs:ident $to_32_lhs:ident,
@ -677,7 +687,7 @@ pub fn eval_const_expr_partial<'tcx>(tcx: &ty::ctxt<'tcx>,
ast::ExprUnary(ast::UnNot, ref inner) => {
match try!(eval_const_expr_partial(tcx, &**inner, ety)) {
const_int(i) => const_int(!i),
const_uint(i) => const_uint(!i),
const_uint(i) => const_uint_not(i, expr_uint_type),
const_bool(b) => const_bool(!b),
const_str(_) => signal!(e, NotOnString),
const_float(_) => signal!(e, NotOnFloat),

21
src/test/run-pass/issue-23968-const-not-overflow.rs Normal file
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@ -0,0 +1,21 @@
// 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 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
const U8_MAX_HALF: u8 = !0u8 / 2;
const U16_MAX_HALF: u16 = !0u16 / 2;
const U32_MAX_HALF: u32 = !0u32 / 2;
const U64_MAX_HALF: u64 = !0u64 / 2;
fn main() {
assert_eq!(U8_MAX_HALF, 0x7f);
assert_eq!(U16_MAX_HALF, 0x7fff);
assert_eq!(U32_MAX_HALF, 0x7fff_ffff);
assert_eq!(U64_MAX_HALF, 0x7fff_ffff_ffff_ffff);
}