wc: Perf gains with the bytecount crate.

Issue #7494
Improve performace of wc app.
 - Use the bytecount::num_chars API to count UTF-8 characters in a file.
 - Enable runtime-dispatch-simd feature in the bytecount crate.

src/uu/wc/BENCHMARKING.md

@@ -26,10 +26,11 @@ output of uutils `cat` into it. Note that GNU `cat` is slower and therefore less
 suitable, and that if a file is given as its input directly (as in
 `wc -c < largefile`) the first strategy kicks in. Try `uucat somefile | wc -c`.
 
-### Counting lines
+### Counting lines and UTF-8 characters
 
-In the case of `wc -l` or `wc -cl` the input doesn't have to be decoded. It's
-read in chunks and the `bytecount` crate is used to count the newlines.
+If the flags set are a subset of `-clm` then the input doesn't have to be decoded. The
+input is read in chunks and the `bytecount` crate is used to count the newlines (`-l` flag) 
+and/or UTF-8 characters (`-m` flag).
 
 It's useful to vary the line length in the input. GNU wc seems particularly
 bad at short lines.

src/uu/wc/Cargo.toml

@@ -19,7 +19,7 @@ path = "src/wc.rs"
 [dependencies]
 clap = { workspace = true }
 uucore = { workspace = true, features = ["pipes", "quoting-style"] }
-bytecount = { workspace = true }
+bytecount = { workspace = true, features = ["runtime-dispatch-simd"] }
 thiserror = { workspace = true }
 unicode-width = { workspace = true }
 

src/uu/wc/src/count_fast.rs

@@ -212,11 +212,6 @@ pub(crate) fn count_bytes_chars_and_lines_fast<
 >(
     handle: &mut R,
 ) -> (WordCount, Option<io::Error>) {
-    /// Mask of the value bits of a continuation byte
-    const CONT_MASK: u8 = 0b0011_1111u8;
-    /// Value of the tag bits (tag mask is !CONT_MASK) of a continuation byte
-    const TAG_CONT_U8: u8 = 0b1000_0000u8;
-
     let mut total = WordCount::default();
     let mut buf = [0; BUF_SIZE];
     loop {
@@ -227,10 +222,7 @@ pub(crate) fn count_bytes_chars_and_lines_fast<
                     total.bytes += n;
                 }
                 if COUNT_CHARS {
-                    total.chars += buf[..n]
-                        .iter()
-                        .filter(|&&byte| (byte & !CONT_MASK) != TAG_CONT_U8)
-                        .count();
+                    total.chars += bytecount::num_chars(&buf[..n]);
                 }
                 if COUNT_LINES {
                     total.lines += bytecount::count(&buf[..n], b'\n');