- /* ============================================================= */
- /* COPYRIGHT (C) 1986 Gary S. Brown. You may use this program, or */
- /* code or tables extracted from it, as desired without restriction. */
- /* */
- /* First, the polynomial itself and its table of feedback terms. The */
- /* polynomial is */
- /* X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0 */
- /* */
- /* Note that we take it "backwards" and put the highest-order term in */
- /* the lowest-order bit. The X^32 term is "implied"; the LSB is the */
- /* X^31 term, etc. The X^0 term (usually shown as "+1") results in */
- /* the MSB being 1. */
- /* */
- /* Note that the usual hardware shift register implementation, which */
- /* is what we're using (we're merely optimizing it by doing eight-bit */
- /* chunks at a time) shifts bits into the lowest-order term. In our */
- /* implementation, that means shifting towards the right. Why do we */
- /* do it this way? Because the calculated CRC must be transmitted in */
- /* order from highest-order term to lowest-order term. UARTs transmit */
- /* characters in order from LSB to MSB. By storing the CRC this way, */
- /* we hand it to the UART in the order low-byte to high-byte; the UART */
- /* sends each low-bit to hight-bit; and the result is transmission bit */
- /* by bit from highest- to lowest-order term without requiring any bit */
- /* shuffling on our part. Reception works similarly. */
- /* */
- /* The feedback terms table consists of 256, 32-bit entries. Notes: */
- /* */
- /* The table can be generated at runtime if desired; code to do so */
- /* is shown later. It might not be obvious, but the feedback */
- /* terms simply represent the results of eight shift/xor opera- */
- /* tions for all combinations of data and CRC register values. */
- /* */
- /* The values must be right-shifted by eight bits by the "updcrc" */
- /* logic; the shift must be unsigned (bring in zeroes). On some */
- /* hardware you could probably optimize the shift in assembler by */
- /* using byte-swap instructions. */
- /* polynomial $edb88320 */
- /* */
- /* -------------------------------------------------------------------- */
-
-static unsigned int crc32_tab[] = {