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| author | bors <bors@rust-lang.org> | 2014-07-03 06:11:38 +0000 |
|---|---|---|
| committer | bors <bors@rust-lang.org> | 2014-07-03 06:11:38 +0000 |
| commit | 00f9ff2b41ffd1f1c187533570d979018724852a (patch) | |
| tree | 3213e9e5f8328493feb5bc417d55f2460f117c8b | |
| parent | e6c54a12c4d209de9f438b4722657ca381f969a2 (diff) | |
| parent | c0248c0839cfdf5b7030f4191ea7aed0981b9e4e (diff) | |
| download | rust-00f9ff2b41ffd1f1c187533570d979018724852a.tar.gz rust-00f9ff2b41ffd1f1c187533570d979018724852a.zip | |
auto merge of #15324 : sneves/rust/master, r=alexcrichton
The current implementation of `rotate_left` and `rotate_right` are incorrect when the rotation amount is 0, or a multiple of the input's bitsize. When `n = 0`, the expression
(self >> n) | (self << ($BITS - n))
results in a shift left by `$BITS` bits, which is undefined behavior (see https://github.com/rust-lang/rust/issues/10183), and currently results in a hardcoded `-1` value, instead of the original input value. Reducing `($BITS - n)` modulo `$BITS`, simplified to `(-n % $BITS)`, fixes this problem.
| -rw-r--r-- | src/libcore/num/mod.rs | 4 | ||||
| -rw-r--r-- | src/libcoretest/num/int_macros.rs | 9 | ||||
| -rw-r--r-- | src/libcoretest/num/uint_macros.rs | 9 |
3 files changed, 20 insertions, 2 deletions
diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs index b32e4167da1..1fae362471d 100644 --- a/src/libcore/num/mod.rs +++ b/src/libcore/num/mod.rs @@ -586,14 +586,14 @@ macro_rules! int_impl { fn rotate_left(self, n: uint) -> $T { // Protect against undefined behaviour for over-long bit shifts let n = n % $BITS; - (self << n) | (self >> ($BITS - n)) + (self << n) | (self >> (($BITS - n) % $BITS)) } #[inline] fn rotate_right(self, n: uint) -> $T { // Protect against undefined behaviour for over-long bit shifts let n = n % $BITS; - (self >> n) | (self << ($BITS - n)) + (self >> n) | (self << (($BITS - n) % $BITS)) } #[inline] diff --git a/src/libcoretest/num/int_macros.rs b/src/libcoretest/num/int_macros.rs index 940b036ca90..d078b514085 100644 --- a/src/libcoretest/num/int_macros.rs +++ b/src/libcoretest/num/int_macros.rs @@ -114,6 +114,15 @@ mod tests { assert_eq!(_1.rotate_left(124), _1); assert_eq!(_0.rotate_right(124), _0); assert_eq!(_1.rotate_right(124), _1); + + // Rotating by 0 should have no effect + assert_eq!(A.rotate_left(0), A); + assert_eq!(B.rotate_left(0), B); + assert_eq!(C.rotate_left(0), C); + // Rotating by a multiple of word size should also have no effect + assert_eq!(A.rotate_left(64), A); + assert_eq!(B.rotate_left(64), B); + assert_eq!(C.rotate_left(64), C); } #[test] diff --git a/src/libcoretest/num/uint_macros.rs b/src/libcoretest/num/uint_macros.rs index 2272af67daf..aefaa90520e 100644 --- a/src/libcoretest/num/uint_macros.rs +++ b/src/libcoretest/num/uint_macros.rs @@ -74,6 +74,15 @@ mod tests { assert_eq!(_1.rotate_left(124), _1); assert_eq!(_0.rotate_right(124), _0); assert_eq!(_1.rotate_right(124), _1); + + // Rotating by 0 should have no effect + assert_eq!(A.rotate_left(0), A); + assert_eq!(B.rotate_left(0), B); + assert_eq!(C.rotate_left(0), C); + // Rotating by a multiple of word size should also have no effect + assert_eq!(A.rotate_left(64), A); + assert_eq!(B.rotate_left(64), B); + assert_eq!(C.rotate_left(64), C); } #[test] |