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

src/liblibc

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

src/libstd/ffi/c_str.rs

@@ -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) }),
         }

src/libstd/io/buffered.rs

@@ -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) }

src/libstd/io/mod.rs

@@ -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)

src/libstd/lib.rs

@@ -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;

src/libstd/memchr.rs

@@ -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"));
+    }
+}

src/libstd/sys/unix/os.rs

@@ -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()),