Skip to content

Optimize pointer alignment in utf8 validation #61339

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 2 commits into from
Jul 17, 2019
Merged

Optimize pointer alignment in utf8 validation #61339

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
3d2c4ff
Optimize pointer alignment in utf8 validation
jridgewell May 30, 2019
3b6e8ed
Do not use pointer alignment on unsupported platforms
jridgewell Jul 5, 2019
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
9 changes: 3 additions & 6 deletions src/libcore/str/mod.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1417,6 +1417,7 @@ fn run_utf8_validation(v: &[u8]) -> Result<(), Utf8Error> {
let usize_bytes = mem::size_of::<usize>();
let ascii_block_size = 2 * usize_bytes;
let blocks_end = if len >= ascii_block_size { len - ascii_block_size + 1 } else { 0 };
let align = v.as_ptr().align_offset(usize_bytes);

while index < len {
let old_offset = index;
Expand Down Expand Up @@ -1496,12 +1497,8 @@ fn run_utf8_validation(v: &[u8]) -> Result<(), Utf8Error> {
// Ascii case, try to skip forward quickly.
// When the pointer is aligned, read 2 words of data per iteration
// until we find a word containing a non-ascii byte.
let ptr = v.as_ptr();
let align = unsafe {
// the offset is safe, because `index` is guaranteed inbounds
ptr.add(index).align_offset(usize_bytes)
};
if align == 0 {
if align != usize::max_value() && align.wrapping_sub(index) % usize_bytes == 0 {
let ptr = v.as_ptr();
while index < blocks_end {
unsafe {
let block = ptr.add(index) as *const usize;
Expand Down