Skip to content

Optimize u64_to_{le,be}_bytes #11973

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Feb 1, 2014
Merged

Optimize u64_to_{le,be}_bytes #11973

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
42 changes: 14 additions & 28 deletions src/libstd/io/extensions.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -51,23 +51,16 @@ impl<'r, R: Reader> Iterator<u8> for Bytes<'r, R> {
}

pub fn u64_to_le_bytes<T>(n: u64, size: uint, f: |v: &[u8]| -> T) -> T {
use unstable::intrinsics::{to_le16, to_le32, to_le64};
use cast::transmute;

// LLVM fails to properly optimize this when using shifts instead of the to_le* intrinsics
assert!(size <= 8u);
match size {
1u => f(&[n as u8]),
2u => f(&[n as u8,
(n >> 8) as u8]),
4u => f(&[n as u8,
(n >> 8) as u8,
(n >> 16) as u8,
(n >> 24) as u8]),
8u => f(&[n as u8,
(n >> 8) as u8,
(n >> 16) as u8,
(n >> 24) as u8,
(n >> 32) as u8,
(n >> 40) as u8,
(n >> 48) as u8,
(n >> 56) as u8]),
2u => f(unsafe { transmute::<i16, [u8, ..2]>(to_le16(n as i16)) }),
4u => f(unsafe { transmute::<i32, [u8, ..4]>(to_le32(n as i32)) }),
8u => f(unsafe { transmute::<i64, [u8, ..8]>(to_le64(n as i64)) }),
_ => {

let mut bytes: ~[u8] = ~[];
Expand All @@ -84,23 +77,16 @@ pub fn u64_to_le_bytes<T>(n: u64, size: uint, f: |v: &[u8]| -> T) -> T {
}

pub fn u64_to_be_bytes<T>(n: u64, size: uint, f: |v: &[u8]| -> T) -> T {
use unstable::intrinsics::{to_be16, to_be32, to_be64};
use cast::transmute;

// LLVM fails to properly optimize this when using shifts instead of the to_be* intrinsics
assert!(size <= 8u);
match size {
1u => f(&[n as u8]),
2u => f(&[(n >> 8) as u8,
n as u8]),
4u => f(&[(n >> 24) as u8,
(n >> 16) as u8,
(n >> 8) as u8,
n as u8]),
8u => f(&[(n >> 56) as u8,
(n >> 48) as u8,
(n >> 40) as u8,
(n >> 32) as u8,
(n >> 24) as u8,
(n >> 16) as u8,
(n >> 8) as u8,
n as u8]),
2u => f(unsafe { transmute::<i16, [u8, ..2]>(to_be16(n as i16)) }),
4u => f(unsafe { transmute::<i32, [u8, ..4]>(to_be32(n as i32)) }),
8u => f(unsafe { transmute::<i64, [u8, ..8]>(to_be64(n as i64)) }),
_ => {
let mut bytes: ~[u8] = ~[];
let mut i = size;
Expand Down