diff mbox series

memchr.3: Deprecate rawmemchr(3)

Message ID 20230105190246.17819-1-alx@kernel.org
State Not applicable
Headers
Series memchr.3: Deprecate rawmemchr(3) |

Checks

Context Check Description
dj/TryBot-apply_patch fail Patch failed to apply to master at the time it was sent
dj/TryBot-32bit fail Patch series failed to apply

Commit Message

Alejandro Colomar Jan. 5, 2023, 7:02 p.m. UTC 
  It is not optimized, and it calls either strlen(3) or memchr(3), so the
caller can do it directly, and it will be better.

Suggested-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
---
 man3/memchr.3 | 28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

Comments

Wilco Dijkstra Jan. 6, 2023, 12:57 p.m. UTC | #1 
Hi Alex,

> It is not optimized, and it calls either strlen(3) or memchr(3), so the
> caller can do it directly, and it will be better.
>
> Suggested-by: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
> Signed-off-by: Alejandro Colomar <alx@kernel.org>

This looks good to me. Btw in the codesearch there are about 800
uses, the majority looks like prototypes etc, so there are few actual
uses. Interestingly GLIBC still contains this:

#ifdef _LIBC
      p = __rawmemchr (p, '\0');
#else
      p = strchr (p, '\0');
#endif

The strchr (p, 0) is optimized by compilers into strlen (since that's
obviously the right optimization) so adding rawmemchr was not
only wasted effort, but it made things slower as well. So we should
remove these uses from GLIBC.

Cheers,
Wilco
diff mbox series

Patch

diff --git a/man3/memchr.3 b/man3/memchr.3
index 68873964e..e03001bec 100644
--- a/man3/memchr.3
+++ b/man3/memchr.3
@@ -22,7 +22,8 @@  .SH SYNOPSIS
 .PP
 .BI "void *memchr(const void " s [. n "], int " c ", size_t " n );
 .BI "void *memrchr(const void " s [. n "], int " c ", size_t " n );
-.BI "void *rawmemchr(const void " s [. n "], int " c );
+.PP
+.BI "[[deprecated]] void *rawmemchr(const void " s [. n "], int " c );
 .fi
 .PP
 .RS -4
@@ -66,26 +67,21 @@  .SH DESCRIPTION
 The
 .BR rawmemchr ()
 function is similar to
-.BR memchr ():
-it assumes (i.e., the programmer knows for certain)
+.BR memchr (),
+but it assumes
+(i.e., the programmer knows for certain)
 that an instance of
 .I c
 lies somewhere in the memory area starting at the location pointed to by
-.IR s ,
-and so performs an optimized search for
-.I c
-(i.e., no use of a count argument to limit the range of the search).
+.IR s .
 If an instance of
 .I c
-is not found, the results are unpredictable.
-The following call is a fast means of locating a string's
-terminating null byte:
-.PP
-.in +4n
-.EX
-char *p = rawmemchr(s,\ \(aq\e0\(aq);
-.EE
-.in
+is not found, the behavior is undefined.
+Use either
+.BR strlen (3)
+or
+.BR memchr (3)
+instead.
 .SH RETURN VALUE
 The
 .BR memchr ()