wsutil: Add a memrchr implementation

Use the system memrchr if found, otherwise use a very basic
non optimized implementation

ConfigureChecks.cmake

@@ -104,6 +104,7 @@ if(UNIX)
 	cmake_push_check_state()
 	list(APPEND CMAKE_REQUIRED_DEFINITIONS -D_GNU_SOURCE)
 	check_symbol_exists("memmem"        "string.h"   HAVE_MEMMEM)
+	check_symbol_exists("memrchr"       "string.h"   HAVE_MEMRCHR)
 	check_symbol_exists("strerrorname_np" "string.h" HAVE_STRERRORNAME_NP)
 	check_symbol_exists("strptime"      "time.h"     HAVE_STRPTIME)
 	check_symbol_exists("vasprintf"     "stdio.h"    HAVE_VASPRINTF)

cmakeconfig.h.in

@@ -280,6 +280,9 @@
 /* Define if you have the 'memmem' function. */
 #cmakedefine HAVE_MEMMEM 1
 
+/* Define if you have the 'memrchr' function. */
+#cmakedefine HAVE_MEMRCHR 1
+
 /* Define if you have the 'strerrorname_np' function. */
 #cmakedefine HAVE_STRERRORNAME_NP 1
 

packaging/debian/libwsutil0.symbols

@@ -490,6 +490,7 @@ libwsutil.so.0 libwsutil0 #MINVER#
  ws_memmem@Base 3.7.0
  ws_mempbrk_compile@Base 1.99.4
  ws_mempbrk_exec@Base 1.99.4
+ ws_memrchr@Base 4.3.0rc0
  ws_optarg@Base 3.5.1
  ws_opterr@Base 3.5.1
  ws_optind@Base 3.5.1

wsutil/str_util.c

@@ -339,6 +339,36 @@ ws_ascii_strcasestr(const char *haystack, const char *needle)
     return NULL;
 }
 
+/* Return the last occurrence of ch in the n bytes of haystack.
+ * If not found or n is 0, return NULL. */
+const uint8_t *
+ws_memrchr(const void *_haystack, int ch, size_t n)
+{
+#ifdef HAVE_MEMRCHR
+    return memrchr(_haystack, ch, n);
+#else
+    /* A generic implementation. This could be optimized considerably,
+     * e.g. by fetching a word at a time.
+     */
+    if (n == 0) {
+        return NULL;
+    }
+    const uint8_t *haystack = _haystack;
+    const uint8_t *p;
+    uint8_t c = (uint8_t)ch;
+
+    const uint8_t *const end = haystack + n - 1;
+
+    for (p = end; p >= haystack; --p) {
+        if (*p == c) {
+            return p;
+        }
+    }
+
+    return NULL;
+#endif /* HAVE_MEMRCHR */
+}
+
 #define FORMAT_SIZE_UNIT_MASK 0x00ff
 #define FORMAT_SIZE_PFX_MASK 0xff00
 

wsutil/str_util.h

@@ -182,6 +182,17 @@ bool isdigit_string(const unsigned char *str);
 WS_DLL_PUBLIC
 const char *ws_ascii_strcasestr(const char *haystack, const char *needle);
 
+/** Like the memchr() function, except it scans backwards from the end.
+ *
+ * @param haystack Pointer to the bytes of memory to search
+ * @param ch The character to search
+ * @param n The length of bytes to search from the end
+ * @return A pointer to the last occurrence of "ch" in "haystack".
+ * If "ch" isn't found or "n" is 0, returns NULL.
+ */
+WS_DLL_PUBLIC
+const uint8_t *ws_memrchr(const void *haystack, int ch, size_t n);
+
 WS_DLL_PUBLIC
 char *ws_escape_string(wmem_allocator_t *alloc, const char *string, bool add_quotes);