freepascal.compiler/packages/paszlib/gzcrcasm.pas

Unit GZCrcAsm;

{
  crc32.c -- compute the CRC-32 of a data stream
  Copyright (C) 1995-1998 Mark Adler

  Pascal translation
  Copyright (C) 1998 by Jacques Nomssi Nzali
  For conditions of distribution and use, see copyright notice in readme.txt

  Assembler for FPC by Marco van de Voort, originating from a Modula-2 port
  which originated from either SWAG sources or the RA development kit. (not
  tracable anymore)
}

interface

{$I zconf.inc}

{$IFNDEF FPC}
  'CRC32 assembler version specific for the Free Pascal compiler'
{$ELSE}
  {-- $DEFINE TightLoop}
{$ENDIF}

uses
  zutil, zbase;

function crc32(crc : uLong; buf : pBytef; len : uInt) : uLong;

{  Update a running crc with the bytes buf[0..len-1] and return the updated
   crc. If buf is NULL, this function returns the required initial value
   for the crc. Pre- and post-conditioning (one's complement) is performed
   within this function so it shouldn't be done by the application.
   Usage example:

    var
      crc : uLong;
    begin
      crc := crc32(0, Z_NULL, 0);

      while (read_buffer(buffer, length) <> EOF) do
        crc := crc32(crc, buffer, length);

      if (crc <> original_crc) then error();
    end;

}

function get_crc_table : puLong;  { can be used by asm versions of crc32() }


implementation

{$IFDEF DYNAMIC_CRC_TABLE}

{local}
const
  crc_table_empty : boolean = TRUE;
{local}
var
  crc_table : array[0..256-1] of uLongf;


{
  Generate a table for a byte-wise 32-bit CRC calculation on the polynomial:
  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.

  Polynomials over GF(2) are represented in binary, one bit per coefficient,
  with the lowest powers in the most significant bit.  Then adding polynomials
  is just exclusive-or, and multiplying a polynomial by x is a right shift by
  one.  If we call the above polynomial p, and represent a byte as the
  polynomial q, also with the lowest power in the most significant bit (so the
  byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
  where a mod b means the remainder after dividing a by b.

  This calculation is done using the shift-register method of multiplying and
  taking the remainder.  The register is initialized to zero, and for each
  incoming bit, x^32 is added mod p to the register if the bit is a one (where
  x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
  x (which is shifting right by one and adding x^32 mod p if the bit shifted
  out is a one).  We start with the highest power (least significant bit) of
  q and repeat for all eight bits of q.

  The table is simply the CRC of all possible eight bit values.  This is all
  the information needed to generate CRC's on data a byte at a time for all
  combinations of CRC register values and incoming bytes.
}
{local}
procedure make_crc_table;
var
 c    : uLong;
 n,k  : int;
 poly : uLong; { polynomial exclusive-or pattern }

const
 { terms of polynomial defining this crc (except x^32): }
 p: array [0..13] of Byte = (0,1,2,4,5,7,8,10,11,12,16,22,23,26);

begin
  { make exclusive-or pattern from polynomial ($EDB88320) }
  poly := Long(0);
  for n := 0 to (sizeof(p) div sizeof(Byte))-1 do
    poly := poly or (Long(1) shl (31 - p[n]));

  for n := 0 to 255 do
  begin
    c := uLong(n);
    for k := 0 to 7 do
    begin
      if (c and 1) <> 0 then
        c := poly xor (c shr 1)
      else
        c := (c shr 1);
    end;
    crc_table[n] := c;
  end;
  crc_table_empty := FALSE;
end;

{$ELSE}

{ ========================================================================
  Table of CRC-32's of all single-byte values (made by make_crc_table) }

{local}
const
  crc_table : array[0..256-1] of uLongf = (
  $00000000, $77073096, $ee0e612c, $990951ba, $076dc419,
  $706af48f, $e963a535, $9e6495a3, $0edb8832, $79dcb8a4,
  $e0d5e91e, $97d2d988, $09b64c2b, $7eb17cbd, $e7b82d07,
  $90bf1d91, $1db71064, $6ab020f2, $f3b97148, $84be41de,
  $1adad47d, $6ddde4eb, $f4d4b551, $83d385c7, $136c9856,
  $646ba8c0, $fd62f97a, $8a65c9ec, $14015c4f, $63066cd9,
  $fa0f3d63, $8d080df5, $3b6e20c8, $4c69105e, $d56041e4,
  $a2677172, $3c03e4d1, $4b04d447, $d20d85fd, $a50ab56b,
  $35b5a8fa, $42b2986c, $dbbbc9d6, $acbcf940, $32d86ce3,
  $45df5c75, $dcd60dcf, $abd13d59, $26d930ac, $51de003a,
  $c8d75180, $bfd06116, $21b4f4b5, $56b3c423, $cfba9599,
  $b8bda50f, $2802b89e, $5f058808, $c60cd9b2, $b10be924,
  $2f6f7c87, $58684c11, $c1611dab, $b6662d3d, $76dc4190,
  $01db7106, $98d220bc, $efd5102a, $71b18589, $06b6b51f,
  $9fbfe4a5, $e8b8d433, $7807c9a2, $0f00f934, $9609a88e,
  $e10e9818, $7f6a0dbb, $086d3d2d, $91646c97, $e6635c01,
  $6b6b51f4, $1c6c6162, $856530d8, $f262004e, $6c0695ed,
  $1b01a57b, $8208f4c1, $f50fc457, $65b0d9c6, $12b7e950,
  $8bbeb8ea, $fcb9887c, $62dd1ddf, $15da2d49, $8cd37cf3,
  $fbd44c65, $4db26158, $3ab551ce, $a3bc0074, $d4bb30e2,
  $4adfa541, $3dd895d7, $a4d1c46d, $d3d6f4fb, $4369e96a,
  $346ed9fc, $ad678846, $da60b8d0, $44042d73, $33031de5,
  $aa0a4c5f, $dd0d7cc9, $5005713c, $270241aa, $be0b1010,
  $c90c2086, $5768b525, $206f85b3, $b966d409, $ce61e49f,
  $5edef90e, $29d9c998, $b0d09822, $c7d7a8b4, $59b33d17,
  $2eb40d81, $b7bd5c3b, $c0ba6cad, $edb88320, $9abfb3b6,
  $03b6e20c, $74b1d29a, $ead54739, $9dd277af, $04db2615,
  $73dc1683, $e3630b12, $94643b84, $0d6d6a3e, $7a6a5aa8,
  $e40ecf0b, $9309ff9d, $0a00ae27, $7d079eb1, $f00f9344,
  $8708a3d2, $1e01f268, $6906c2fe, $f762575d, $806567cb,
  $196c3671, $6e6b06e7, $fed41b76, $89d32be0, $10da7a5a,
  $67dd4acc, $f9b9df6f, $8ebeeff9, $17b7be43, $60b08ed5,
  $d6d6a3e8, $a1d1937e, $38d8c2c4, $4fdff252, $d1bb67f1,
  $a6bc5767, $3fb506dd, $48b2364b, $d80d2bda, $af0a1b4c,
  $36034af6, $41047a60, $df60efc3, $a867df55, $316e8eef,
  $4669be79, $cb61b38c, $bc66831a, $256fd2a0, $5268e236,
  $cc0c7795, $bb0b4703, $220216b9, $5505262f, $c5ba3bbe,
  $b2bd0b28, $2bb45a92, $5cb36a04, $c2d7ffa7, $b5d0cf31,
  $2cd99e8b, $5bdeae1d, $9b64c2b0, $ec63f226, $756aa39c,
  $026d930a, $9c0906a9, $eb0e363f, $72076785, $05005713,
  $95bf4a82, $e2b87a14, $7bb12bae, $0cb61b38, $92d28e9b,
  $e5d5be0d, $7cdcefb7, $0bdbdf21, $86d3d2d4, $f1d4e242,
  $68ddb3f8, $1fda836e, $81be16cd, $f6b9265b, $6fb077e1,
  $18b74777, $88085ae6, $ff0f6a70, $66063bca, $11010b5c,
  $8f659eff, $f862ae69, $616bffd3, $166ccf45, $a00ae278,
  $d70dd2ee, $4e048354, $3903b3c2, $a7672661, $d06016f7,
  $4969474d, $3e6e77db, $aed16a4a, $d9d65adc, $40df0b66,
  $37d83bf0, $a9bcae53, $debb9ec5, $47b2cf7f, $30b5ffe9,
  $bdbdf21c, $cabac28a, $53b39330, $24b4a3a6, $bad03605,
  $cdd70693, $54de5729, $23d967bf, $b3667a2e, $c4614ab8,
  $5d681b02, $2a6f2b94, $b40bbe37, $c30c8ea1, $5a05df1b,
  $2d02ef8d);

{$ENDIF}

{ =========================================================================
  This function can be used by asm versions of crc32() }

function get_crc_table : {const} puLong;
begin
{$ifdef DYNAMIC_CRC_TABLE}
  if (crc_table_empty) then
    make_crc_table;
{$endif}
  get_crc_table :=  {const} puLong(@crc_table);
end;

{ ========================================================================= }

function crc32 (crc : uLong; buf : pBytef; len : uInt): uLong; ASSEMBLER;

// Original header, old procedure didn't normalize or check for NIL pointer
// (since open array), and check for table-existance.
//
// FUNCTION  Crc32( crc     : CARDINAL;var Buffer;BufSize:CARDINAL):CARDINAL;ASSEMBLER;

ASM
                             mov   buf,%esi             // Load source address
                             xor   %ebx,%ebx
                             test  %esi,%esi
                             je   .LCalcAfterEndLoop    // buf-pointer is NIL
                             mov   crc,%ebx             // load previous CRC
                             xor   $-1,%ebx             // normalize/invert CRC
                             call  get_crc_table
                             mov   %eax,%edi
                             mov   len,%ecx             // Counter.
{$IFNDEF TightLoop}
.LTightTest:                 test $-8,%ecx  // Test if at least 8 bytes left in buffer
                             je   .LCalcEndbigloop

                             lodsb                  // Yes, loop optimalisation
                             movzbl %bl,%edx
                             shrl  $8,%ebx
                             xorb  %al,%dl
                             xorl  (%edi,%edx,4),%ebx

                             // the above base code is copied 7 times. So 7+1=8

                             lodsb                              // 2
                             movzbl %bl,%edx
                             shrl  $8,%ebx
                             xorb  %al,%dl
                             xorl  (%edi,%edx,4),%ebx
                             lodsb                              // 3
                             movzbl %bl,%edx
                             shrl  $8,%ebx
                             xorb  %al,%dl
                             xorl  (%edi,%edx,4),%ebx
                             lodsb                              // 4
                             movzbl %bl,%edx
                             shrl  $8,%ebx
                             xorb  %al,%dl
                             xorl  (%edi,%edx,4),%ebx
                             lodsb                              // 5
                             movzbl %bl,%edx
                             shrl  $8,%ebx
                             xorb  %al,%dl
                             xorl  (%edi,%edx,4),%ebx
                             lodsb                              // 6
                             movzbl %bl,%edx
                             shrl  $8,%ebx
                             xorb  %al,%dl
                             xorl  (%edi,%edx,4),%ebx
                             lodsb                              // 7
                             movzbl %bl,%edx
                             shrl  $8,%ebx
                             xorb  %al,%dl
                             xorl  (%edi,%edx,4),%ebx
                             lodsb                              // 8
                             movzbl %bl,%edx
                             shrl  $8,%ebx
                             xorb  %al,%dl
                             xorl  (%edi,%edx,4),%ebx

                             subl $8,%ecx               // 8 less to go
                             jmp  .LTightTest
.LCalcEndbigloop:            jecxz .LCalcNormalTerm
{$ENDIF}
  .LCalcLoop:                lodsb                      // Do (rest) buffer
                             movzbl %bl,%edx
                             shrl  $8,%ebx
                             xorb  %al,%dl
                             xorl  (%edi,%edx,4),%ebx
                             loop  .LCalcLoop
  .LCalcNormalTerm:          xor   $-1,%ebx             // normalize/invert CRC
  .LCalcAfterEndLoop:        mov   %ebx,%eax
end['EAX','EBX','ECX','EDX','ESI','EDI'];


end.