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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,111 @@ | ||
| #[cfg(not(feature = "runtime-dispatch-simd"))] | ||
| use core::{mem, ptr, usize}; | ||
| #[cfg(feature = "runtime-dispatch-simd")] | ||
| use std::{mem, ptr, usize}; | ||
|
|
||
| fn splat(byte: u8) -> usize { | ||
| let lo = usize::MAX / 0xFF; | ||
| lo * byte as usize | ||
| } | ||
|
|
||
| unsafe fn usize_load_unchecked(bytes: &[u8], offset: usize) -> usize { | ||
| let mut output = 0; | ||
| ptr::copy_nonoverlapping( | ||
| bytes.as_ptr().offset(offset as isize), | ||
| &mut output as *mut usize as *mut u8, | ||
| mem::size_of::<usize>() | ||
| ); | ||
| output | ||
| } | ||
|
|
||
| fn bytewise_equal(lhs: usize, rhs: usize) -> usize { | ||
| let lo = usize::MAX / 0xFF; | ||
| let hi = lo << 7; | ||
|
|
||
| let x = lhs ^ rhs; | ||
| !((((x & !hi) + !hi) | x) >> 7) & lo | ||
| } | ||
|
|
||
| fn sum_usize(values: usize) -> usize { | ||
| let every_other_byte_lo = usize::MAX / 0xFFFF; | ||
| let every_other_byte = every_other_byte_lo * 0xFF; | ||
|
|
||
| // Pairwise reduction to avoid overflow on next step. | ||
| let pair_sum: usize = (values & every_other_byte) + ((values >> 8) & every_other_byte); | ||
|
|
||
| // Multiplication results in top two bytes holding sum. | ||
| pair_sum.wrapping_mul(every_other_byte_lo) >> ((mem::size_of::<usize>() - 2) * 8) | ||
| } | ||
|
|
||
| fn is_leading_utf8_byte(values: usize) -> usize { | ||
| // a leading UTF-8 byte is one which does not start with the bits 10. | ||
| ((!values >> 7) | (values >> 6)) & splat(1) | ||
| } | ||
|
|
||
| pub fn chunk_count(haystack: &[u8], needle: u8) -> usize { | ||
| let chunksize = mem::size_of::<usize>(); | ||
| assert!(haystack.len() >= chunksize); | ||
|
|
||
| unsafe { | ||
| let mut offset = 0; | ||
| let mut count = 0; | ||
|
|
||
| let needles = splat(needle); | ||
|
|
||
| // 2040 | ||
| while haystack.len() >= offset + chunksize * 255 { | ||
| let mut counts = 0; | ||
| for _ in 0..255 { | ||
| counts += bytewise_equal(usize_load_unchecked(haystack, offset), needles); | ||
| offset += chunksize; | ||
| } | ||
| count += sum_usize(counts); | ||
| } | ||
|
|
||
| // 8 | ||
| let mut counts = 0; | ||
| for i in 0..(haystack.len() - offset) / chunksize { | ||
| counts += bytewise_equal(usize_load_unchecked(haystack, offset + i * chunksize), needles); | ||
| } | ||
| if haystack.len() % 8 != 0 { | ||
| let mask = !(!0 >> ((haystack.len() % chunksize) * 8)); | ||
| counts += bytewise_equal(usize_load_unchecked(haystack, haystack.len() - chunksize), needles) & mask; | ||
| } | ||
| count += sum_usize(counts); | ||
|
|
||
| count | ||
| } | ||
| } | ||
|
|
||
| pub fn chunk_num_chars(utf8_chars: &[u8]) -> usize { | ||
| let chunksize = mem::size_of::<usize>(); | ||
| assert!(utf8_chars.len() >= chunksize); | ||
|
|
||
| unsafe { | ||
| let mut offset = 0; | ||
| let mut count = 0; | ||
|
|
||
| // 2040 | ||
| while utf8_chars.len() >= offset + chunksize * 255 { | ||
| let mut counts = 0; | ||
| for _ in 0..255 { | ||
| counts += is_leading_utf8_byte(usize_load_unchecked(utf8_chars, offset)); | ||
| offset += chunksize; | ||
| } | ||
| count += sum_usize(counts); | ||
| } | ||
|
|
||
| // 8 | ||
| let mut counts = 0; | ||
| for i in 0..(utf8_chars.len() - offset) / chunksize { | ||
| counts += is_leading_utf8_byte(usize_load_unchecked(utf8_chars, offset + i * chunksize)); | ||
| } | ||
| if utf8_chars.len() % 8 != 0 { | ||
| let mask = !(!0 >> ((utf8_chars.len() % chunksize) * 8)); | ||
| counts += is_leading_utf8_byte(usize_load_unchecked(utf8_chars, utf8_chars.len() - chunksize)) & mask; | ||
| } | ||
| count += sum_usize(counts); | ||
|
|
||
| count | ||
| } | ||
| } |
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