Ref #1 Fix motorola data format

dbc_decoder.cpp

@@ -111,31 +111,26 @@ bool DbcDecoder::ExtractMotorola (const std::vector<std::uint8_t> &data,
    * - startBit points to the most significant bit of the signal
    * - inside a byte, bit numbering goes 7..0
    * - crossing byte boundary moves to the next byte, bit 7
+   * Example: a signal starting at 7 follows 7..0, 15..8, 23..16.
    */
 
   value = 0U;
 
-  std::int32_t currentBit = static_cast<std::int32_t> (startBit);
+  std::size_t byteIndex = startBit / 8U;
+  std::uint32_t bitInByte = startBit % 8U;
 
   for (std::uint32_t bitIndex = 0U; bitIndex < length; ++bitIndex) {
-    if (currentBit < 0)
-      return false;
-
-    const std::uint32_t absoluteBit = static_cast<std::uint32_t> (currentBit);
-    const std::uint32_t byteIndex = absoluteBit / 8U;
-    const std::uint32_t bitFromMsb = absoluteBit % 8U;
-    const std::uint32_t bitInByte = 7U - bitFromMsb;
-
     if (byteIndex >= data.size())
       return false;
 
     value <<= 1U;
     value |= static_cast<std::uint64_t> ((data[byteIndex] >> bitInByte) & 0x01U);
 
-    if ((absoluteBit % 8U) == 7U)
-      currentBit = static_cast<std::int32_t> ((byteIndex + 1U) * 8U);
-    else
-      --currentBit;
+    if (bitInByte == 0U) {
+      ++byteIndex;
+      bitInByte = 7U;
+    } else
+      --bitInByte;
   }
 
   return true;