add memmem()

memmem() is a nice GNU extension for searching a length limited string
in another one.

This compat version is based on the version found in glibc 2.2 (GPL 2);
I only removed the optimization of checking the first char by hand, and
generally tried to keep the code simple.  We can add it back if memcmp
shows up high in a profile, but for now I prefer to keep it (almost
trivially) simple.

Since I don't really know which platforms beside those with a glibc
have their own memmem(), I used a heuristic: if NO_STRCASESTR is set,
then NO_MEMMEM is set, too.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -28,6 +28,8 @@ all::
 #
 # Define NO_STRCASESTR if you don't have strcasestr.
 #
+# Define NO_MEMMEM if you don't have memmem.
+#
 # Define NO_STRLCPY if you don't have strlcpy.
 #
 # Define NO_STRTOUMAX if you don't have strtoumax in the C library.
@@ -402,6 +404,7 @@ ifeq ($(uname_S),SunOS)
 	NEEDS_NSL = YesPlease
 	SHELL_PATH = /bin/bash
 	NO_STRCASESTR = YesPlease
+	NO_MEMMEM = YesPlease
 	NO_HSTRERROR = YesPlease
 	ifeq ($(uname_R),5.8)
 		NEEDS_LIBICONV = YesPlease
@@ -424,6 +427,7 @@ ifeq ($(uname_O),Cygwin)
 	NO_D_TYPE_IN_DIRENT = YesPlease
 	NO_D_INO_IN_DIRENT = YesPlease
 	NO_STRCASESTR = YesPlease
+	NO_MEMMEM = YesPlease
 	NO_SYMLINK_HEAD = YesPlease
 	NEEDS_LIBICONV = YesPlease
 	NO_FAST_WORKING_DIRECTORY = UnfortunatelyYes
@@ -442,6 +446,7 @@ ifeq ($(uname_S),FreeBSD)
 endif
 ifeq ($(uname_S),OpenBSD)
 	NO_STRCASESTR = YesPlease
+	NO_MEMMEM = YesPlease
 	NEEDS_LIBICONV = YesPlease
 	BASIC_CFLAGS += -I/usr/local/include
 	BASIC_LDFLAGS += -L/usr/local/lib
@@ -456,6 +461,7 @@ ifeq ($(uname_S),NetBSD)
 endif
 ifeq ($(uname_S),AIX)
 	NO_STRCASESTR=YesPlease
+	NO_MEMMEM = YesPlease
 	NO_STRLCPY = YesPlease
 	NEEDS_LIBICONV=YesPlease
 endif
@@ -467,6 +473,7 @@ ifeq ($(uname_S),IRIX64)
 	NO_IPV6=YesPlease
 	NO_SETENV=YesPlease
 	NO_STRCASESTR=YesPlease
+	NO_MEMMEM = YesPlease
 	NO_STRLCPY = YesPlease
 	NO_SOCKADDR_STORAGE=YesPlease
 	SHELL_PATH=/usr/gnu/bin/bash
@@ -661,6 +668,10 @@ ifdef NO_HSTRERROR
 	COMPAT_CFLAGS += -DNO_HSTRERROR
 	COMPAT_OBJS += compat/hstrerror.o
 endif
+ifdef NO_MEMMEM
+	COMPAT_CFLAGS += -DNO_MEMMEM
+	COMPAT_OBJS += compat/memmem.o
+endif
 
 ifeq ($(TCLTK_PATH),)
 NO_TCLTK=NoThanks

compat/memmem.c

@@ -0,0 +1,29 @@
+#include "../git-compat-util.h"
+
+void *gitmemmem(const void *haystack, size_t haystack_len,
+                const void *needle, size_t needle_len)
+{
+	const char *begin = haystack;
+	const char *last_possible = begin + haystack_len - needle_len;
+
+	/*
+	 * The first occurrence of the empty string is deemed to occur at
+	 * the beginning of the string.
+	 */
+	if (needle_len == 0)
+		return (void *)begin;
+
+	/*
+	 * Sanity check, otherwise the loop might search through the whole
+	 * memory.
+	 */
+	if (haystack_len < needle_len)
+		return NULL;
+
+	for (; begin <= last_possible; begin++) {
+		if (!memcmp(begin, needle, needle_len))
+			return (void *)begin;
+	}
+
+	return NULL;
+}

git-compat-util.h

@@ -172,6 +172,12 @@ extern uintmax_t gitstrtoumax(const char *, char **, int);
 extern const char *githstrerror(int herror);
 #endif
 
+#ifdef NO_MEMMEM
+#define memmem gitmemmem
+void *gitmemmem(const void *haystack, size_t haystacklen,
+                const void *needle, size_t needlelen);
+#endif
+
 extern void release_pack_memory(size_t, int);
 
 static inline char* xstrdup(const char *str)