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unit crc;
{
crc32.c -- compute the CRC-32 of a data stream
Copyright (C) 1995-1998 Mark Adler
Pascal tranlastion
Copyright (C) 1998 by Jacques Nomssi Nzali
For conditions of distribution and use, see copyright notice in readme.txt
}
interface
function crc32(crc : cardinal; buf : Pbyte; len : cardinal) : cardinal;
{ 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 : cardinal;
begin
crc := crc32(0, nil, 0);
while (read_buffer(buffer, length) <> EOF) do
crc := crc32(crc, buffer, length);
if (crc <> original_crc) then error();
end;
}
function get_crc_table : Pcardinal; { can be used by asm versions of crc32() }
implementation
{$IFDEF DYNAMIC_CRC_TABLE}
{local}
const
crc_table_empty : boolean = TRUE;
{local}
var
crc_table : array[0..256-1] of uLongf;
{
Generate a table for a byte-wise 32-bit CRC calculation on the polynomial:
x^32+x^26+x^23+x^22+x^16+x^12+x^11+x^10+x^8+x^7+x^5+x^4+x^2+x+1.
Polynomials over GF(2) are represented in binary, one bit per coefficient,
with the lowest powers in the most significant bit. Then adding polynomials
is just exclusive-or, and multiplying a polynomial by x is a right shift by
one. If we call the above polynomial p, and represent a byte as the
polynomial q, also with the lowest power in the most significant bit (so the
byte 0xb1 is the polynomial x^7+x^3+x+1), then the CRC is (q*x^32) mod p,
where a mod b means the remainder after dividing a by b.
This calculation is done using the shift-register method of multiplying and
taking the remainder. The register is initialized to zero, and for each
incoming bit, x^32 is added mod p to the register if the bit is a one (where
x^32 mod p is p+x^32 = x^26+...+1), and the register is multiplied mod p by
x (which is shifting right by one and adding x^32 mod p if the bit shifted
out is a one). We start with the highest power (least significant bit) of
q and repeat for all eight bits of q.
The table is simply the CRC of all possible eight bit values. This is all
the information needed to generate CRC's on data a byte at a time for all
combinations of CRC register values and incoming bytes.
}
{local}
procedure make_crc_table;
var
c : cardinal;
n,k : integer;
poly : cardinal; { polynomial exclusive-or pattern }
const
{ terms of polynomial defining this crc (except x^32): }
p: array [0..13] of Byte = (0,1,2,4,5,7,8,10,11,12,16,22,23,26);
begin
{ make exclusive-or pattern from polynomial ($EDB88320) }
poly := longint(0);
for n := 0 to (sizeof(p) div sizeof(Byte))-1 do
poly := poly or (longint(1) shl (31 - p[n]));
for n := 0 to 255 do
begin
c := cardinal(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 cardinal = (
$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} Pcardinal;
begin
{$ifdef DYNAMIC_CRC_TABLE}
if (crc_table_empty) then
make_crc_table;
{$endif}
get_crc_table := {const} Pcardinal(@crc_table);
end;
{ ========================================================================= }
function crc32 (crc : cardinal; buf : Pbyte; len : cardinal): cardinal;
begin
if (buf = nil) then
crc32 := 0
else
begin
{$IFDEF DYNAMIC_CRC_TABLE}
if crc_table_empty then
make_crc_table;
{$ENDIF}
crc := crc xor cardinal($ffffffff);
while (len >= 8) do
begin
{DO8(buf)}
crc := crc_table[(integer(crc) xor buf^) and $ff] xor (crc shr 8);
inc(buf);
crc := crc_table[(integer(crc) xor buf^) and $ff] xor (crc shr 8);
inc(buf);
crc := crc_table[(integer(crc) xor buf^) and $ff] xor (crc shr 8);
inc(buf);
crc := crc_table[(integer(crc) xor buf^) and $ff] xor (crc shr 8);
inc(buf);
crc := crc_table[(integer(crc) xor buf^) and $ff] xor (crc shr 8);
inc(buf);
crc := crc_table[(integer(crc) xor buf^) and $ff] xor (crc shr 8);
inc(buf);
crc := crc_table[(integer(crc) xor buf^) and $ff] xor (crc shr 8);
inc(buf);
crc := crc_table[(integer(crc) xor buf^) and $ff] xor (crc shr 8);
inc(buf);
dec(len, 8);
end;
if (len <> 0) then
repeat
{DO1(buf)}
crc := crc_table[(integer(crc) xor buf^) and $ff] xor (crc shr 8);
inc(buf);
dec(len);
until (len = 0);
crc32 := crc xor cardinal($ffffffff);
end;
end;
end.
|
