//
//
//           The Nimrod Compiler
//        (c) Copyright 2008 Andreas Rumpf
//
//    See the file "copying.txt", included in this
//    distribution, for details about the copyright.
//
unit crc;

interface

{$include 'config.inc'}

uses
  nsystem, strutils;

type
  TCrc32 = int32;

const
  InitCrc32 = TCrc32(-1);

  InitAdler32 = int32(1);

function updateCrc32(val: Byte; crc: TCrc32): TCrc32; overload;
function updateCrc32(val: Char; crc: TCrc32): TCrc32; overload;

function crcFromBuf(buf: Pointer; len: int): TCrc32;
function strCrc32(const s: string): TCrc32;

function crcFromFile(const filename: string): TCrc32;

function updateAdler32(adler: int32; buf: pointer; len: int): int32;


implementation

{@ignore}
{$ifopt Q+} { we need Q- here! }
  {$define Q_on}
  {$Q-}
{$endif}

{$ifopt R+}
  {$define R_on}
  {$R-}
{$endif}
{@emit}

{@ignore}
type
  TCRC_TabEntry = TCrc32;
{@emit
type
  TCRC_TabEntry = int
}

const
  crc32table: array [0..255] of TCRC_TabEntry = (
    0, 1996959894, -301047508, -1727442502,
    124634137, 1886057615, -379345611, -1637575261,
    249268274, 2044508324, -522852066, -1747789432,
    162941995, 2125561021, -407360249, -1866523247,
    498536548, 1789927666, -205950648, -2067906082,
    450548861, 1843258603, -187386543, -2083289657,
    325883990, 1684777152, -43845254, -1973040660,
    335633487, 1661365465, -99664541, -1928851979,
    997073096, 1281953886, -715111964, -1570279054,
    1006888145, 1258607687, -770865667, -1526024853,
    901097722, 1119000684, -608450090, -1396901568,
    853044451, 1172266101, -589951537, -1412350631,
    651767980, 1373503546, -925412992, -1076862698,
    565507253, 1454621731, -809855591, -1195530993,
    671266974, 1594198024, -972236366, -1324619484,
    795835527, 1483230225, -1050600021, -1234817731,
    1994146192, 31158534, -1731059524, -271249366,
    1907459465, 112637215, -1614814043, -390540237,
    2013776290, 251722036, -1777751922, -519137256,
    2137656763, 141376813, -1855689577, -429695999,
    1802195444, 476864866, -2056965928, -228458418,
    1812370925, 453092731, -2113342271, -183516073,
    1706088902, 314042704, -1950435094, -54949764,
    1658658271, 366619977, -1932296973, -69972891,
    1303535960, 984961486, -1547960204, -725929758,
    1256170817, 1037604311, -1529756563, -740887301,
    1131014506, 879679996, -1385723834, -631195440,
    1141124467, 855842277, -1442165665, -586318647,
    1342533948, 654459306, -1106571248, -921952122,
    1466479909, 544179635, -1184443383, -832445281,
    1591671054, 702138776, -1328506846, -942167884,
    1504918807, 783551873, -1212326853, -1061524307,
    -306674912, -1698712650, 62317068, 1957810842,
    -355121351, -1647151185, 81470997, 1943803523,
    -480048366, -1805370492, 225274430, 2053790376,
    -468791541, -1828061283, 167816743, 2097651377,
    -267414716, -2029476910, 503444072, 1762050814,
    -144550051, -2140837941, 426522225, 1852507879,
    -19653770, -1982649376, 282753626, 1742555852,
    -105259153, -1900089351, 397917763, 1622183637,
    -690576408, -1580100738, 953729732, 1340076626,
    -776247311, -1497606297, 1068828381, 1219638859,
    -670225446, -1358292148, 906185462, 1090812512,
    -547295293, -1469587627, 829329135, 1181335161,
    -882789492, -1134132454, 628085408, 1382605366,
    -871598187, -1156888829, 570562233, 1426400815,
    -977650754, -1296233688, 733239954, 1555261956,
    -1026031705, -1244606671, 752459403, 1541320221,
    -1687895376, -328994266, 1969922972, 40735498,
    -1677130071, -351390145, 1913087877, 83908371,
    -1782625662, -491226604, 2075208622, 213261112,
    -1831694693, -438977011, 2094854071, 198958881,
    -2032938284, -237706686, 1759359992, 534414190,
    -2118248755, -155638181, 1873836001, 414664567,
    -2012718362, -15766928, 1711684554, 285281116,
    -1889165569, -127750551, 1634467795, 376229701,
    -1609899400, -686959890, 1308918612, 956543938,
    -1486412191, -799009033, 1231636301, 1047427035,
    -1362007478, -640263460, 1088359270, 936918000,
    -1447252397, -558129467, 1202900863, 817233897,
    -1111625188, -893730166, 1404277552, 615818150,
    -1160759803, -841546093, 1423857449, 601450431,
    -1285129682, -1000256840, 1567103746, 711928724,
    -1274298825, -1022587231, 1510334235, 755167117
  );

function updateCrc32(val: Byte; crc: TCrc32): TCrc32; overload;
begin
  result := TCrc32(crc32Table[(int(crc) xor (int(val) and $ff)) and $ff]) xor
                  (crc shr TCrc32(8));
end;

function updateCrc32(val: Char; crc: TCrc32): TCrc32; overload;
begin
  result := updateCrc32(byte(ord(val)), crc);
end;

function strCrc32(const s: string): TCrc32;
var
  i: int;
begin
  result := InitCrc32;
  for i := strStart to length(s)+StrStart-1 do
    result := updateCrc32(s[i], result)
end;

type
  TByteArray = array [0..10000000] of Byte;
  PByteArray = ^TByteArray;
function crcFromBuf(buf: Pointer; len: int): TCrc32;
var
  p: PByteArray;
  i: int;
begin
  p := {@cast}PByteArray(buf);
  result := InitCrc32;
  for i := 0 to len-1 do result := updateCrc32(p[i], result)
end;

function crcFromFile(const filename: string): TCrc32;
const
  bufSize = 8 * 1024;
var
  bin: TBinaryFile;
  buf: Pointer;
  readBytes, i: int;
  p: PByteArray;
begin
  result := InitCrc32;
  if not openFile(bin, filename) then exit; // not equal if file does not exist
  buf := alloc(BufSize);
  p := {@cast}PByteArray(buf);
  while true do begin
    readBytes := readBuffer(bin, buf, bufSize);
    for i := 0 to readBytes-1 do result := updateCrc32(p[i], result);
    if readBytes <> bufSize then break;
  end;
  dealloc(buf);
  CloseFile(bin);
end;


const
  base = int32(65521); { largest prime smaller than 65536 }
  {NMAX = 5552; original code with unsigned 32 bit integer }
  { NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 }
  nmax = 3854;        { code with signed 32 bit integer }
  { NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^31-1 }
  { The penalty is the time loss in the extra MOD-calls. }

function updateAdler32(adler: int32; buf: pointer; len: int): int32;
var
  s1, s2: int32;
  L, k, b: int;
begin
  s1 := adler and int32($ffff);
  s2 := (adler shr int32(16)) and int32($ffff);
  L := len;
  b := 0;
  while (L > 0) do begin
    if L < nmax then k := L
    else k := nmax;
    dec(L, k);
    while (k > 0) do begin
      s1 := s1 +{%} int32(({@cast}cstring(buf))[b]);
      s2 := s2 +{%} s1;
      inc(b); dec(k);
    end;
    s1 := modu(s1, base);
    s2 := modu(s2, base);
  end;
  result := (s2 shl int32(16)) or s1;
end;

{@ignore}
{$ifdef Q_on}
  {$undef Q_on}
  {$Q+}
{$endif}

{$ifdef R_on}
  {$undef R_on}
  {$R+}
{$endif}
{@emit}

end.