string: add and test a naive memrchr (DONE)

CMakeLists.txt

@@ -190,6 +190,7 @@ set(SOURCES
   src/libc/string/memcmp.c
   src/libc/string/memcpy.c
   src/libc/string/memmove.c
+  src/libc/string/memrchr.c
   src/libc/string/memset.c
   src/libc/string/strcasecmp.c
   src/libc/string/strcasestr.c

STATUS

@@ -200,6 +200,7 @@ TEST:       Function/symbol/macro needs to be tested
      (EXT)     strncasecmp                   -
      (EXT)     strdup                        -
      (EXT)     strndup                       -
+     (EXT)     memrchr                       -
 
 7.22 <tgmath.h> => GCC
 

include/string.h

@@ -54,6 +54,9 @@ extern size_t strxfrm(char * __restrict__ __dest,
 /* Search __c within the first __n characters of __s. */
 extern void *memchr(void const *__s, int __c, size_t __n);
 
+/* Search the last occurrence of __c withing the first __n bytes of __s. */
+extern void *memrchr(void const *__s, int __c, size_t __n);
+
 /* Find the first occurrence of __c within __s. */
 extern char *strchr(char const *__s, int __c);
 

src/libc/string/memrchr.c

@@ -0,0 +1,12 @@
+#include <string.h>
+
+void *memrchr(void const *_s, int c, size_t n)
+{
+	char const *s = _s;
+
+	for(int i = n - 1; i >= 0; i--) {
+		if(s[i] == c) return (char *)&s[i];
+	}
+
+	return NULL;
+}