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>

1 files changed, 29 insertions, 0 deletions

diff --git a/compat/memmem.c b/compat/memmem.c
new file mode 100644
index 000000000..cd0d87736
--- /dev/null
+++ b/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;
+}