code.delx.au - refind/blob - refind/crc32.h

   1 /*-
   2  *  COPYRIGHT (C) 1986 Gary S. Brown.  You may use this program, or
   3  *  code or tables extracted from it, as desired without restriction.
   4  *
   5  *  First, the polynomial itself and its table of feedback terms.  The
   6  *  polynomial is
   7  *  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
   8  *
   9  *  Note that we take it "backwards" and put the highest-order term in
  10  *  the lowest-order bit.  The X^32 term is "implied"; the LSB is the
  11  *  X^31 term, etc.  The X^0 term (usually shown as "+1") results in
  12  *  the MSB being 1
  13  *
  14  *  Note that the usual hardware shift register implementation, which
  15  *  is what we're using (we're merely optimizing it by doing eight-bit
  16  *  chunks at a time) shifts bits into the lowest-order term.  In our
  17  *  implementation, that means shifting towards the right.  Why do we
  18  *  do it this way?  Because the calculated CRC must be transmitted in
  19  *  order from highest-order term to lowest-order term.  UARTs transmit
  20  *  characters in order from LSB to MSB.  By storing the CRC this way
  21  *  we hand it to the UART in the order low-byte to high-byte; the UART
  22  *  sends each low-bit to hight-bit; and the result is transmission bit
  23  *  by bit from highest- to lowest-order term without requiring any bit
  24  *  shuffling on our part.  Reception works similarly
  25  *
  26  *  The feedback terms table consists of 256, 32-bit entries.  Notes
  27  *
  28  *      The table can be generated at runtime if desired; code to do so
  29  *      is shown later.  It might not be obvious, but the feedback
  30  *      terms simply represent the results of eight shift/xor opera
  31  *      tions for all combinations of data and CRC register values
  32  *
  33  *      The values must be right-shifted by eight bits by the "updcrc
  34  *      logic; the shift must be unsigned (bring in zeroes).  On some
  35  *      hardware you could probably optimize the shift in assembler by
  36  *      using byte-swap instructions
  37  *      polynomial $edb88320
  38  *
  39  *
  40  * CRC32 code derived from work by Gary S. Brown.
  41  */
  42 /*
  43  * Modified slightly for use on EFI by Rod Smith
  44  */
  45
  46 #ifndef __CRC32_H_
  47 #define __CRC32_H_
  48
  49 #ifdef __MAKEWITH_GNUEFI
  50 #include "efi.h"
  51 #include "efilib.h"
  52 #else
  53 #include "../include/tiano_includes.h"
  54 #endif
  55
  56 UINT32 crc32(UINT32 crc, const VOID *buf, UINTN size);
  57
  58 #endif