updated crc algorithm to a more efficient implementation

lib-bms-protocol/src/types.rs

@@ -332,7 +332,7 @@ pub fn check_hemming(data: u32, hemming: u8) -> Result<(), HemmingCorrectionValu
 
 /// CRC-6 calculation using polynomial 0x21 (MSB first)
 ///
-/// This function calculates a 6-bit CRC for 26 bits of data.
+/// This function calculates a 6-bit CRC for a u32 value.
 /// The polynomial used is 0x21 in the crc world polynoms
 /// are named after the bit pattern with implicit assumption
 /// of the trailing 1, thus 0x21 become 0x43 referring to
@@ -349,18 +349,15 @@ pub fn check_hemming(data: u32, hemming: u8) -> Result<(), HemmingCorrectionValu
 /// - All double-bit errors
 /// - Random errors with a probability of 2^-6 = 0.015625 of going undetected
 pub fn calc_crc6(data: u32) -> u8 {
-    let mut working_data: u32 = data << 6;
-    let mut polynom: u32 = 0x43 << 25;
-    let mut mask: u32 = 0x40 << 25;
-    while working_data >= 0x40 {
-        if working_data & mask != 0 {
-            working_data ^= polynom;
+    let mut crc: u8 = 0x00; 
+    for pos in 0..32 {
+        if ((data >> (31-pos)) & 0x1) ^ ((crc >> 5) & 0x1) as u32 != 0 {
+            crc = ((crc << 1) ^ 0x03) & 0x3F;
         } else {
-            polynom >>= 1;
-            mask >>= 1;
+            crc = (crc << 1) & 0x3F;
         }
     }
-    (working_data & 0x3f) as u8
+    crc
 }
 
 /// CRC-6 checking