LittleFS: correct CRC calculation

features/storage/filesystem/littlefs/LittleFileSystem.cpp

@@ -24,7 +24,7 @@ namespace mbed {
 
 extern "C" void lfs_crc(uint32_t *crc, const void *buffer, size_t size)
 {
-    uint32_t initial_xor = *crc;
+    uint32_t initial_xor = lfs_rbit(*crc);
     // lfs_cache_crc calls lfs_crc for every byte individually, so can't afford
     // start-up overhead for hardware acceleration. Limit to table-based.
     MbedCRC<POLY_32BIT_ANSI, 32, CrcMode::TABLE> ct(initial_xor, 0x0, true, true);

features/storage/filesystem/littlefs/TESTS/filesystem/seek/main.cpp

@@ -535,7 +535,7 @@ void test_boundary_seek_and_write()
         size = strlen("hedgehoghog");
         const off_t offsets[] = {512, 1020, 513, 1021, 511, 1019};
 
-        for (int i = 0; i < sizeof(offsets) / sizeof(offsets[0]); i++) {
+        for (size_t i = 0; i < sizeof(offsets) / sizeof(offsets[0]); i++) {
             off_t off = offsets[i];
             memcpy(buffer, "hedgehoghog", size);
             res = file[0].seek(off, SEEK_SET);

features/storage/filesystem/littlefs/littlefs/lfs_util.h

@@ -47,6 +47,7 @@ extern "C"
 #ifdef __MBED__
 #include "mbed_debug.h"
 #include "mbed_assert.h"
+#include "cmsis_compiler.h"
 #else
 #define MBED_LFS_ENABLE_INFO   false
 #define MBED_LFS_ENABLE_DEBUG  true
@@ -183,6 +184,21 @@ static inline uint32_t lfs_tole32(uint32_t a) {
     return lfs_fromle32(a);
 }
 
+// Reverse the bits in a
+static inline uint32_t lfs_rbit(uint32_t a) {
+#if !defined(LFS_NO_INTRINSICS) && MBED_LFS_INTRINSICS && \
+    defined(__MBED__)
+    return __RBIT(a);
+#else
+    a = ((a & 0xaaaaaaaa) >> 1) | ((a & 0x55555555) << 1);
+    a = ((a & 0xcccccccc) >> 2) | ((a & 0x33333333) << 2);
+    a = ((a & 0xf0f0f0f0) >> 4) | ((a & 0x0f0f0f0f) << 4);
+    a = ((a & 0xff00ff00) >> 8) | ((a & 0x00ff00ff) << 8);
+    a = (a >> 16) | (a << 16);
+    return a;
+#endif
+}
+
 // Calculate CRC-32 with polynomial = 0x04c11db7
 void lfs_crc(uint32_t *crc, const void *buffer, size_t size);