mikros/rust
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Merge pull request #117 from cassiersg/fix-round-power-of-two

Browse Source 
Use wrapping operations for bit-level functions
This commit is contained in:
Nick Cameron 2015-06-22 10:37:29 -07:00
commit 3bb144c26e
1 changed files with 5 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
src/utils.rs
View File

@ -119,26 +119,26 @@ pub fn format_visibility(vis: Visibility) -> &'static str {
// Based on the trick layed out at
// http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
pub fn round_up_to_power_of_two(mut x: usize) -> usize {
x -= 1;
x = x.wrapping_sub(1);
x |= x >> 1;
x |= x >> 2;
x |= x >> 4;
x |= x >> 8;
x |= x >> 16;
x |= x >> 32;
x + 1
x.wrapping_add(1)
}
#[inline]
#[cfg(target_pointer_width="32")]
pub fn round_up_to_power_of_two(mut x: usize) -> usize {
x -= 1;
x = x.wrapping_sub(1);
x |= x >> 1;
x |= x >> 2;
x |= x >> 4;
x |= x >> 8;
x |= x >> 16;
x + 1
x.wrapping_add(1)
}
// Macro for deriving implementations of Decodable for enums
@ -161,6 +161,7 @@ macro_rules! impl_enum_decodable {
#[test]
fn power_rounding() {
assert_eq!(0, round_up_to_power_of_two(0));
assert_eq!(1, round_up_to_power_of_two(1));
assert_eq!(64, round_up_to_power_of_two(33));
assert_eq!(256, round_up_to_power_of_two(256));