OpenE2K/rust
2
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

Add memchr implemenation based on rust-memchr to libstd

Browse Source
This commit is contained in:
Florian Hahn 2015-12-12 23:38:03 +01:00
parent 27d551142f
commit ca52c56e34
2 changed files with 402 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/libstd/lib.rs
View File

@ -248,6 +248,7 @@
#![feature(link_args)]
#![feature(linkage)]
#![feature(macro_reexport)]
#![feature(num_bits_bytes)]
#![feature(on_unimplemented)]
#![feature(oom)]
#![feature(optin_builtin_traits)]
@ -429,6 +430,7 @@ pub mod path;
pub mod process;
pub mod sync;
pub mod time;
mod memchr;
#[macro_use]
#[path = "sys/common/mod.rs"] mod sys_common;

400
src/libstd/memchr.rs Normal file
View File

@ -0,0 +1,400 @@
// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//
// Original implementation taken from rust-memchr
// Copyright 2015 Andrew Gallant, bluss and Nicolas Koch
use libc::{c_void, c_int, size_t};
/// A safe interface to `memchr`.
///
/// Returns the index corresponding to the first occurrence of `needle` in
/// `haystack`, or `None` if one is not found.
///
/// memchr reduces to super-optimized machine code at around an order of
/// magnitude faster than `haystack.iter().position(|&b| b == needle)`.
/// (See benchmarks.)
///
/// # Example
///
/// This shows how to find the first position of a byte in a byte string.
///
/// ```rust
/// use memchr::memchr;
///
/// let haystack = b"the quick brown fox";
/// assert_eq!(memchr(b'k', haystack), Some(8));
/// ```
pub fn memchr(needle: u8, haystack: &[u8]) -> Option<usize> {
// libc memchr
#[cfg(any(not(target_os = "windows"),
not(any(target_pointer_width = "32",
target_pointer_width = "64"))))]
fn memchr_specific(needle: u8, haystack: &[u8]) -> Option<usize> {
use libc::memchr as libc_memchr;
let p = unsafe {
libc_memchr(
haystack.as_ptr() as *const c_void,
needle as c_int,
haystack.len() as size_t)
};
if p.is_null() {
None
} else {
Some(p as usize - (haystack.as_ptr() as usize))
}
}
// use fallback on windows, since it's faster
#[cfg(all(target_os = "windows",
any(target_pointer_width = "32",
target_pointer_width = "64")))]
fn memchr_specific(needle: u8, haystack: &[u8]) -> Option<usize> {
fallback::memchr(needle, haystack)
}
memchr_specific(needle, haystack)
}
/// A safe interface to `memrchr`.
///
/// Returns the index corresponding to the last occurrence of `needle` in
/// `haystack`, or `None` if one is not found.
///
/// # Example
///
/// This shows how to find the last position of a byte in a byte string.
///
/// ```rust
/// use memchr::memrchr;
///
/// let haystack = b"the quick brown fox";
/// assert_eq!(memrchr(b'o', haystack), Some(17));
/// ```
pub fn memrchr(needle: u8, haystack: &[u8]) -> Option<usize> {
#[cfg(target_os = "linux")]
fn memrchr_specific(needle: u8, haystack: &[u8]) -> Option<usize> {
use libc::memrchr as libc_memrchr;
// GNU's memrchr() will - unlike memchr() - error if haystack is empty.
if haystack.is_empty() {return None}
let p = unsafe {
libc_memrchr(
haystack.as_ptr() as *const c_void,
needle as c_int,
haystack.len() as size_t)
};
if p.is_null() {
None
} else {
Some(p as usize - (haystack.as_ptr() as usize))
}
}
#[cfg(all(not(target_os = "linux"),
any(target_pointer_width = "32", target_pointer_width = "64")))]
fn memrchr_specific(needle: u8, haystack: &[u8]) -> Option<usize> {
fallback::memrchr(needle, haystack)
}
// For the rare case of neither 32 bit nor 64-bit platform.
#[cfg(all(not(target_os = "linux"),
not(target_pointer_width = "32"),
not(target_pointer_width = "64")))]
fn memrchr_specific(needle: u8, haystack: &[u8]) -> Option<usize> {
haystack.iter().rposition(|&b| b == needle)
}
memrchr_specific(needle, haystack)
}
#[allow(dead_code)]
mod fallback {
use cmp;
use usize;
const LO_U64: u64 = 0x0101010101010101;
const HI_U64: u64 = 0x8080808080808080;
// use truncation
const LO_USIZE: usize = LO_U64 as usize;
const HI_USIZE: usize = HI_U64 as usize;
/// Return `true` if `x` contains any zero byte.
///
/// From *Matters Computational*, J. Arndt
///
/// "The idea is to subtract one from each of the bytes and then look for
/// bytes where the borrow propagated all the way to the most significant
/// bit."
#[inline]
fn contains_zero_byte(x: usize) -> bool {
x.wrapping_sub(LO_USIZE) & !x & HI_USIZE != 0
}
#[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
}
/// Return the first index matching the byte `a` in `text`.
pub fn memchr(x: u8, text: &[u8]) -> Option<usize> {
// Scan for a single byte value by reading two `usize` words at a time.
//
// Split `text` in three parts
// - unaligned inital part, before the first word aligned address in text
// - body, scan by 2 words at a time
// - the last remaining part, < 2 word size
let len = text.len();
let ptr = text.as_ptr();
// search up to an aligned boundary
let align = (ptr as usize) & (usize::BYTES- 1);
let mut offset;
if align > 0 {
offset = cmp::min(usize::BYTES - align, len);
if let Some(index) = text[..offset].iter().position(|elt| *elt == x) {
return Some(index);
}
} else {
offset = 0;
}
// search the body of the text
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);
// break if there is a matching byte
let zu = contains_zero_byte(u ^ repeated_x);
let zv = contains_zero_byte(v ^ repeated_x);
if zu || zv {
break;
}
}
offset += usize::BYTES * 2;
}
}
// find the byte after the point the body loop stopped
text[offset..].iter().position(|elt| *elt == x).map(|i| offset + i)
}
/// Return the last index matching the byte `a` in `text`.
pub fn memrchr(x: u8, text: &[u8]) -> Option<usize> {
// Scan for a single byte value by reading two `usize` words at a time.
//
// Split `text` in three parts
// - unaligned tail, after the last word aligned address in text
// - body, scan by 2 words at a time
// - the first remaining bytes, < 2 word size
let len = text.len();
let ptr = text.as_ptr();
// search to an aligned boundary
let end_align = (ptr as usize + len) & (usize::BYTES - 1);
let mut offset;
if end_align > 0 {
offset = len - cmp::min(usize::BYTES - end_align, len);
if let Some(index) = text[offset..].iter().rposition(|elt| *elt == x) {
return Some(offset + index);
}
} else {
offset = len;
}
// search the body of the text
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);
// break if there is a matching byte
let zu = contains_zero_byte(u ^ repeated_x);
let zv = contains_zero_byte(v ^ repeated_x);
if zu || zv {
break;
}
}
offset -= 2 * usize::BYTES;
}
// find the byte before the point the body loop stopped
text[..offset].iter().rposition(|elt| *elt == x)
}
// test fallback implementations on all plattforms
#[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"));
}
}
#[cfg(test)]
mod tests {
// test the implementations for the current plattform
use super::{memchr, memrchr};
#[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"));
}
}