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/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;