sys/string_utils: add reverse_buf()

sys/include/string_utils.h

@@ -179,6 +179,14 @@ ssize_t strscpy(char *dest, const char *src, size_t count);
  */
 const void *memchk(const void *data, uint8_t c, size_t len);
 
+/**
+ * @brief   Reverse the order of bytes in a buffer
+ *
+ * @param[in, out]  buf     The buffer to reverse
+ * @param[in]       len     Size of the buffer
+ */
+void reverse_buf(void *buf, size_t len);
+
 #ifdef __cplusplus
 }
 #endif

sys/libc/string.c

@@ -80,4 +80,15 @@ int __swprintf(string_writer_t *sw, FLASH_ATTR const char *restrict format, ...)
     return res;
 }
 
+void reverse_buf(void *buf, size_t len)
+{
+    uint8_t *cur = buf;
+    uint8_t *end = cur + len - 1;
+    while (cur < end) {
+        uint8_t tmp = *cur;
+        *cur++ = *end;
+        *end-- = tmp;
+    }
+}
+
 /** @} */