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Auto merge of #30381 - fhahn:memchr-in-std, r=alexcrichton 

This PR adds `memchr`and `memrchr` based on @BurntSushi 's rust-memchr crate to libstd (as discussed in #30151).

I've update some places in libstd to use memchr/memrchr, but I am not sure if there are other places where it could be used as well.

ref #30076
This commit is contained in:
bors 2015-12-19 00:57:25 +00:00
parent 9e278950c2 a206e556d0
commit 8ad12c3e25
7 changed files with 397 additions and 5 deletions
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2
src/liblibc

@ -1 +1 @@
Subproject commit 867c6ff0b824d6d295951ed34bb252d5e0b2467a
Subproject commit 9863d5645fc4d1be789d03bcf58c1b3cfafbba39

3
src/libstd/ffi/c_str.rs
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@ -19,6 +19,7 @@ use io;
use iter::Iterator;
use libc;
use mem;
use memchr;
use ops::Deref;
use option::Option::{self, Some, None};
use os::raw::c_char;
@ -188,7 +189,7 @@ impl CString {
}
fn _new(bytes: Vec<u8>) -> Result<CString, NulError> {
match bytes.iter().position(|x| *x == 0) {
match memchr::memchr(0, &bytes) {
Some(i) => Err(NulError(i, bytes)),
None => Ok(unsafe { CString::from_vec_unchecked(bytes) }),
}

3
src/libstd/io/buffered.rs
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@ -18,6 +18,7 @@ use cmp;
use error;
use fmt;
use io::{self, DEFAULT_BUF_SIZE, Error, ErrorKind, SeekFrom};
use memchr;
/// The `BufReader` struct adds buffering to any reader.
///
@ -746,7 +747,7 @@ impl<W: Write> LineWriter<W> {
#[stable(feature = "rust1", since = "1.0.0")]
impl<W: Write> Write for LineWriter<W> {
fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
match buf.iter().rposition(|b| *b == b'\n') {
match memchr::memrchr(b'\n', buf) {
Some(i) => {
let n = try!(self.inner.write(&buf[..i + 1]));
if n != i + 1 { return Ok(n) }

3
src/libstd/io/mod.rs
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@ -254,6 +254,7 @@ use result;
use string::String;
use str;
use vec::Vec;
use memchr;
#[stable(feature = "rust1", since = "1.0.0")]
pub use self::buffered::{BufReader, BufWriter, LineWriter};
@ -1194,7 +1195,7 @@ fn read_until<R: BufRead + ?Sized>(r: &mut R, delim: u8, buf: &mut Vec<u8>)
Err(ref e) if e.kind() == ErrorKind::Interrupted => continue,
Err(e) => return Err(e)
};
match available.iter().position(|x| *x == delim) {
match memchr::memchr(delim, available) {
Some(i) => {
buf.extend_from_slice(&available[..i + 1]);
(true, i + 1)

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;

386
src/libstd/memchr.rs Normal file
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@ -0,0 +1,386 @@
// 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
/// 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,ignore
/// 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(not(target_os = "windows"))]
fn memchr_specific(needle: u8, haystack: &[u8]) -> Option<usize> {
use libc;
let p = unsafe {
libc::memchr(
haystack.as_ptr() as *const libc::c_void,
needle as libc::c_int,
haystack.len() as libc::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(target_os = "windows")]
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,ignore
/// 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;
// 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 libc::c_void,
needle as libc::c_int,
haystack.len() as libc::size_t)
};
if p.is_null() {
None
} else {
Some(p as usize - (haystack.as_ptr() as usize))
}
}
#[cfg(not(target_os = "linux"))]
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"));
}
}

3
src/libstd/sys/unix/os.rs
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@ -22,6 +22,7 @@ use io;
use iter;
use libc::{self, c_int, c_char, c_void};
use mem;
use memchr;
use path::{self, PathBuf};
use ptr;
use slice;
@ -406,7 +407,7 @@ pub fn env() -> Env {
if input.is_empty() {
return None;
}
let pos = input[1..].iter().position(|&b| b == b'=').map(|p| p + 1);
let pos = memchr::memchr(b'=', &input[1..]).map(|p| p + 1);
pos.map(|p| (
OsStringExt::from_vec(input[..p].to_vec()),
OsStringExt::from_vec(input[p+1..].to_vec()),