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use cmp;
use mem;
const LO_U64: u64 = 0x0101010101010101;
const HI_U64: u64 = 0x8080808080808080;
const LO_USIZE: usize = LO_U64 as usize;
const HI_USIZE: usize = HI_U64 as usize;
#[inline]
fn contains_zero_byte(x: usize) -> bool {
x.wrapping_sub(LO_USIZE) & !x & HI_USIZE != 0
}
#[cfg(target_pointer_width = "16")]
#[inline]
fn repeat_byte(b: u8) -> usize {
(b as usize) << 8 | b as usize
}
#[cfg(target_pointer_width = "32")]
#[inline]
fn repeat_byte(b: u8) -> usize {
let mut rep = (b as usize) << 8 | b as usize;
rep = rep << 16 | rep;
rep
}
#[cfg(target_pointer_width = "64")]
#[inline]
fn repeat_byte(b: u8) -> usize {
let mut rep = (b as usize) << 8 | b as usize;
rep = rep << 16 | rep;
rep = rep << 32 | rep;
rep
}
pub fn memchr(x: u8, text: &[u8]) -> Option<usize> {
let len = text.len();
let ptr = text.as_ptr();
let usize_bytes = mem::size_of::<usize>();
let mut offset = ptr.align_offset(usize_bytes);
if offset > 0 {
offset = cmp::min(offset, len);
if let Some(index) = text[..offset].iter().position(|elt| *elt == x) {
return Some(index);
}
}
let repeated_x = repeat_byte(x);
if len >= 2 * usize_bytes {
while offset <= len - 2 * usize_bytes {
unsafe {
let u = *(ptr.offset(offset as isize) as *const usize);
let v = *(ptr.offset((offset + usize_bytes) as isize) as *const usize);
let zu = contains_zero_byte(u ^ repeated_x);
let zv = contains_zero_byte(v ^ repeated_x);
if zu || zv {
break;
}
}
offset += usize_bytes * 2;
}
}
text[offset..].iter().position(|elt| *elt == x).map(|i| offset + i)
}
pub fn memrchr(x: u8, text: &[u8]) -> Option<usize> {
let len = text.len();
let ptr = text.as_ptr();
let usize_bytes = mem::size_of::<usize>();
let end_align = (ptr as usize + len) & (usize_bytes - 1);
let mut offset;
if end_align > 0 {
offset = if end_align >= len { 0 } else { len - end_align };
if let Some(index) = text[offset..].iter().rposition(|elt| *elt == x) {
return Some(offset + index);
}
} else {
offset = len;
}
let repeated_x = repeat_byte(x);
while offset >= 2 * usize_bytes {
unsafe {
let u = *(ptr.offset(offset as isize - 2 * usize_bytes as isize) as *const usize);
let v = *(ptr.offset(offset as isize - usize_bytes as isize) as *const usize);
let zu = contains_zero_byte(u ^ repeated_x);
let zv = contains_zero_byte(v ^ repeated_x);
if zu || zv {
break;
}
}
offset -= 2 * usize_bytes;
}
text[..offset].iter().rposition(|elt| *elt == x)
}
#[test]
fn matches_one() {
assert_eq!(Some(0), memchr(b'a', b"a"));
}
#[test]
fn matches_begin() {
assert_eq!(Some(0), memchr(b'a', b"aaaa"));
}
#[test]
fn matches_end() {
assert_eq!(Some(4), memchr(b'z', b"aaaaz"));
}
#[test]
fn matches_nul() {
assert_eq!(Some(4), memchr(b'\x00', b"aaaa\x00"));
}
#[test]
fn matches_past_nul() {
assert_eq!(Some(5), memchr(b'z', b"aaaa\x00z"));
}
#[test]
fn no_match_empty() {
assert_eq!(None, memchr(b'a', b""));
}
#[test]
fn no_match() {
assert_eq!(None, memchr(b'a', b"xyz"));
}
#[test]
fn matches_one_reversed() {
assert_eq!(Some(0), memrchr(b'a', b"a"));
}
#[test]
fn matches_begin_reversed() {
assert_eq!(Some(3), memrchr(b'a', b"aaaa"));
}
#[test]
fn matches_end_reversed() {
assert_eq!(Some(0), memrchr(b'z', b"zaaaa"));
}
#[test]
fn matches_nul_reversed() {
assert_eq!(Some(4), memrchr(b'\x00', b"aaaa\x00"));
}
#[test]
fn matches_past_nul_reversed() {
assert_eq!(Some(0), memrchr(b'z', b"z\x00aaaa"));
}
#[test]
fn no_match_empty_reversed() {
assert_eq!(None, memrchr(b'a', b""));
}
#[test]
fn no_match_reversed() {
assert_eq!(None, memrchr(b'a', b"xyz"));
}
#[test]
fn each_alignment_reversed() {
let mut data = [1u8; 64];
let needle = 2;
let pos = 40;
data[pos] = needle;
for start in 0..16 {
assert_eq!(Some(pos - start), memrchr(needle, &data[start..]));
}
}