/*- * 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 * * * CRC32 code derived from work by Gary S. Brown.
*/
#include"crc32c.h"
/* CRC32C routines, these use a different polynomial */ /*****************************************************************/ /* */ /* CRC LOOKUP TABLE */ /* ================ */ /* The following CRC lookup table was generated automagically */ /* by the Rocksoft^tm Model CRC Algorithm Table Generation */ /* Program V1.0 using the following model parameters: */ /* */ /* Width : 4 bytes. */ /* Poly : 0x1EDC6F41L */ /* Reverse : TRUE. */ /* */ /* For more information on the Rocksoft^tm Model CRC Algorithm, */ /* see the document titled "A Painless Guide to CRC Error */ /* Detection Algorithms" by Ross Williams */ /* (ross@guest.adelaide.edu.au.). This document is likely to be */ /* in the FTP archive "ftp.adelaide.edu.au/pub/rocksoft". */ /* */ /*****************************************************************/
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