fix reference impl

tests/crc_test.c

@@ -39,15 +39,34 @@ typedef uint32_t(crc_fn)(const uint8_t *input, int length, uint32_t previousCrc3
 
 // Slow reference implementation that computes a 32-bit bit-reflected/bit-inverted CRC using the provided polynomial.
 static uint32_t s_crc_32_reference(const uint8_t *input, int length, const uint32_t previousCrc, uint32_t polynomial) {
-
-    uint32_t crc = ~previousCrc;
-    while (length-- > 0) {
-        crc ^= *input++;
-        for (int j = 8; j > 0; --j) {
-            crc = (crc >> 1) ^ ((((crc & 1) ^ 1) - 1) & polynomial);
+    if (aws_is_big_endian()) {
+        uint32_t crc = 0xFFFFFFFF;
+
+        for (size_t i = 0; i < length; i++) {
+            uint8_t byte = input[i];
+
+            // Process each bit of the byte, starting from MSB
+            for (int j = 7; j >= 0; j--) {
+                uint32_t bit = (byte >> j) & 1;
+                uint32_t c = (crc >> 31) & 1;
+                crc = crc << 1;
+                if (c ^ bit) {
+                    crc = crc ^ polynomial;
+                }
+            }
+        }
+
+        return ~crc; 
+    } else {
+        uint32_t crc = ~previousCrc;
+        while (length-- > 0) {
+            crc ^= *input++;
+            for (int j = 8; j > 0; --j) {
+                crc = (crc >> 1) ^ ((((crc & 1) ^ 1) - 1) & polynomial);
+            }
         }
+        return ~crc;
     }
-    return ~crc;
 }
 
 // Very, very slow reference implementation that computes a CRC32.