lib/littlefs: Add littlefs v2.1.3 source.

lib/littlefs/lfs2_util.c

@@ -0,0 +1,33 @@
+/*
+ * lfs2 util functions
+ *
+ * Copyright (c) 2017, Arm Limited. All rights reserved.
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+#include "lfs2_util.h"
+
+// Only compile if user does not provide custom config
+#ifndef LFS2_CONFIG
+
+
+// Software CRC implementation with small lookup table
+uint32_t lfs2_crc(uint32_t crc, const void *buffer, size_t size) {
+    static const uint32_t rtable[16] = {
+        0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac,
+        0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c,
+        0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c,
+        0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c,
+    };
+
+    const uint8_t *data = buffer;
+
+    for (size_t i = 0; i < size; i++) {
+        crc = (crc >> 4) ^ rtable[(crc ^ (data[i] >> 0)) & 0xf];
+        crc = (crc >> 4) ^ rtable[(crc ^ (data[i] >> 4)) & 0xf];
+    }
+
+    return crc;
+}
+
+
+#endif