diff options
| -rw-r--r-- | NEWS | 2 | ||||
| -rw-r--r-- | src/wc.c | 31 |
2 files changed, 33 insertions, 0 deletions
@@ -94,6 +94,8 @@ GNU coreutils NEWS -*- outline -*- stat and tail now know about IBRIX. stat -f --format=%T now reports the file system type, and tail -f uses polling for files on IBRIX file systems. + wc -l processes short lines much more efficiently. + References from --help and the man pages of utilities have been corrected in various cases, and more direct links to the corresponding online documentation are provided. @@ -264,6 +264,8 @@ wc (int fd, char const *file_x, struct fstatus *fstatus, off_t current_pos) { /* Use a separate loop when counting only lines or lines and bytes -- but not chars or words. */ + bool long_lines = false; + bool check_len = true; while ((bytes_read = safe_read (fd, buf, BUFFER_SIZE)) > 0) { char *p = buf; @@ -275,12 +277,41 @@ wc (int fd, char const *file_x, struct fstatus *fstatus, off_t current_pos) break; } + char *end = p + bytes_read; + + /* Avoid function call overhead for shorter lines. */ + if (check_len) + while (p != end) + { + lines += *p++ == '\n'; + /* If there are more than 150 chars in the first 10 lines, + then use memchr, where system specific optimizations + may outweigh function call overhead. + FIXME: This line length was determined in 2015, on both + x86_64 and ppc64, but it's worth re-evaluating in future with + newer compilers, CPUs, or memchr() implementations etc. */ + if (lines <= 10) + { + if (p - buf > 150) + { + long_lines = true; + break; + } + } + } + else if (! long_lines) + while (p != end) + lines += *p++ == '\n'; + + /* memchr is more efficient with longer lines. */ while ((p = memchr (p, '\n', (buf + bytes_read) - p))) { ++p; ++lines; } + bytes += bytes_read; + check_len = false; } } #if MB_LEN_MAX > 1 |