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wc: count_fast seek optimization

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zhitkoff 2023-12-01 20:18:15 -05:00 committed by Yury Zhytkou
parent 6186153a08
commit 85e78376fe
1 changed files with 5 additions and 3 deletions
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8
src/uu/wc/src/count_fast.rs
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@ -100,7 +100,8 @@ pub(crate) fn count_bytes_fast<T: WordCountable>(handle: &mut T) -> (usize, Opti
// would count up only to a couple of bytes. // would count up only to a couple of bytes.
// This condition usually occurs for files in pseudo-filesystems like /proc, /sys // This condition usually occurs for files in pseudo-filesystems like /proc, /sys
// that report `st_size` in the multiples of system page size. // that report `st_size` in the multiples of system page size.
// In such cases - attempt `seek()` for the end of file // In such cases - attempt `seek()` almost to the end of the file
// and then fall back on read to count the rest.
// //
// And finally a special case of input redirection in *nix shell: // And finally a special case of input redirection in *nix shell:
// `( wc -c ; wc -c ) < file` should return // `( wc -c ; wc -c ) < file` should return
@ -127,8 +128,9 @@ pub(crate) fn count_bytes_fast<T: WordCountable>(handle: &mut T) -> (usize, Opti
// with size that is NOT a multiple of system page size // with size that is NOT a multiple of system page size
return (stat.st_size as usize, None); return (stat.st_size as usize, None);
} else if let Some(file) = handle.inner_file() { } else if let Some(file) = handle.inner_file() {
if let Ok(n) = file.seek(SeekFrom::End(0)) { let offset = stat.st_size - stat.st_size % (stat.st_blksize as i64 + 1);
return (n as usize, None); if let Ok(n) = file.seek(SeekFrom::Start(offset as u64)) {
byte_count = n as usize;
} }
} }
} }