libs/libc/string/lib_memrchr.c: Add memrchr() function

include/string.h

@@ -89,6 +89,7 @@ FAR char  *strtok_r(FAR char *, FAR const char *, FAR char **);
 size_t     strxfrm(FAR char *, FAR const char *, size_t n);
 
 FAR void  *memchr(FAR const void *s, int c, size_t n);
+FAR void  *memrchr(FAR const void *s, int c, size_t n);
 FAR void  *memccpy(FAR void *s1, FAR const void *s2, int c, size_t n);
 int        memcmp(FAR const void *s1, FAR const void *s2, size_t n);
 FAR void  *memcpy(FAR void *dest, FAR const void *src, size_t n);

libs/libc/string/Make.defs

@@ -1,7 +1,7 @@
 ############################################################################
 # libs/libc/string/Make.defs
 #
-#   Copyright (C) 2011-2012, 2014, 2016-2017 Gregory Nutt. All rights reserved.
+#   Copyright (C) 2011-2012, 2014, 2016-2018 Gregory Nutt. All rights reserved.
 #   Author: Gregory Nutt <gnutt@nuttx.org>
 #
 # Redistribution and use in source and binary forms, with or without
@@ -37,9 +37,9 @@
 
 CSRCS += lib_ffs.c lib_ffsl.c lib_ffsll.c lib_fls.c lib_flsl.c
 CSRCS += lib_flsll.c lib_isbasedigit.c lib_memset.c lib_memchr.c
-CSRCS += lib_memccpy.c lib_memcmp.c lib_memmove.c lib_skipspace.c
-CSRCS += lib_stpcpy.c lib_stpncpy.c lib_strcasecmp.c lib_strcat.c
-CSRCS += lib_strchr.c lib_strcpy.c lib_strcmp.c lib_strcspn.c
+CSRCS += lib_memccpy.c lib_memcmp.c lib_memmove.c lib_memrchr.c
+CSRCS += lib_skipspace.c lib_stpcpy.c lib_stpncpy.c lib_strcasecmp.c
+CSRCS += lib_strcat.c lib_strchr.c lib_strcpy.c lib_strcmp.c lib_strcspn.c
 CSRCS += lib_strdup.c lib_strerror.c lib_strlen.c lib_strnlen.c
 CSRCS += lib_strncasecmp.c lib_strncat.c lib_strncmp.c lib_strncpy.c
 CSRCS += lib_strndup.c lib_strcasestr.c lib_strpbrk.c lib_strrchr.c

libs/libc/string/lib_memrchr.c

@@ -0,0 +1,75 @@
+/****************************************************************************
+ * libs/libc/string/lib_memchr.c
+ *
+ *   Copyright (C) 2018 Pinecone Inc. All rights reserved.
+ *   Author: Xiang Xiao <xiaoxiang@pinecone.net>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <string.h>
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: memrchr
+ *
+ * Description:
+ *   The memrchr() function locates the last occurrence of 'c' (converted to
+ *   an unsigned char) in the initial 'n' bytes (each interpreted as
+ *   unsigned char) of the object pointed to by s.
+ *
+ * Returned Value:
+ *   The memrchr() function returns a pointer to the located byte, or a null
+ *   pointer if the byte does not occur in the object.
+ *
+ ****************************************************************************/
+
+FAR void *memrchr(FAR const void *s, int c, size_t n)
+{
+  FAR const unsigned char *p = (FAR const unsigned char *)s + n;
+
+  while (n--)
+    {
+      if (*--p == (unsigned char)c)
+        {
+          return (FAR void *)p;
+        }
+    }
+
+  return NULL;
+}