CRC-32 Hash

Unit: CRC32

Fast 32-bit hash using table lookup (ISO 3309, polynomial $EDB88320). Compatible with PHP crc32(), ZIP, PNG, gzip.

Overview

CRC32 produces a 32-bit (4-byte) hash from arbitrary input data. Used for:

High score tamper protection (HISCORE.PAS)
Save game checksums
File integrity verification

Basic Usage

Hash a String

uses CRC32;

var
  hash: String;
begin
  hash := CRC32String('hello');
  WriteLn(hash);  { Outputs: 3610a686 }
end;

Hash a File

uses CRC32;

var
  CRC: TCRC32;
begin
  if CRC32File('DATA\FONT.PCX', CRC) then
    WriteLn('CRC: ', CRC32ToHex(CRC))
  else
    WriteLn('Error reading file');
end;

Incremental Hashing

For data processed in chunks (used by HISCORE.PAS):

uses CRC32;

var
  CRC: TCRC32;
begin
  CRC32Init(CRC);

  { Process data in chunks }
  CRC32Update(CRC, @buffer1, len1);
  CRC32Update(CRC, @buffer2, len2);

  { Finalize and get result }
  CRC32Final(CRC);
  WriteLn(CRC32ToHex(CRC));
end;

API Reference

Types

TCRC32

TCRC32 = LongInt;

32-bit CRC value.

Core Functions

CRC32Init

procedure CRC32Init(var CRC: TCRC32);

Initialize CRC state to $FFFFFFFF. Call before first CRC32Update.

CRC32Update

procedure CRC32Update(var CRC: TCRC32; Buf: Pointer; Len: Word);

Add data to hash. Can be called multiple times.

Buf: Pointer to data buffer
Len: Number of bytes to hash (max 65535)

CRC32Final

procedure CRC32Final(var CRC: TCRC32);

Finalize hash (XOR with $FFFFFFFF). Call after all CRC32Update calls.

Convenience Functions

CRC32String

function CRC32String(const S: String): String;

Hash a Pascal string, return 8-character hex result.

CRC32File

function CRC32File(const Path: String; var CRC: TCRC32): Boolean;

Hash entire file. Returns True on success, False on I/O error.

CRC32ToHex

function CRC32ToHex(CRC: TCRC32): String;

Convert 32-bit CRC to 8-character lowercase hex string.

PHP Compatibility

Output matches PHP 8’s crc32() function:

echo dechex(crc32("123456789")); // cbf43926
echo dechex(crc32("hello"));     // 3610a686

Same polynomial (0xEDB88320), same algorithm (CRC-32B / ISO 3309).

Test Vectors

Verified against PHP crc32():

CRC32("")            = 00000000
CRC32("a")           = e8b7be43
CRC32("abc")         = 352441c2
CRC32("123456789")   = cbf43926
CRC32("hello")       = 3610a686
CRC32("message digest") = 20159d7f

Implementation Notes

Lookup table: 256-entry table (1KB) computed at unit initialization
Polynomial: $EDB88320 (reflected form of $04C11DB7)
Algorithm: One XOR + one table lookup + one shift per byte
No assembly: Pure Pascal, works on any x86 CPU
No initialization call needed: Table built automatically via unit begin..end block

Performance

Fast on all target hardware (286+):

Input Size	Time (286 @ 12 MHz)
32 bytes	< 1ms
256 bytes	< 1ms
4 KB	~5ms
64 KB	~80ms

Files

UNITS\CRC32.PAS - Main implementation
TESTS\CRCTEST.PAS - Test vectors (PHP-compatible)
TESTS\CCRCTEST.BAT - Compile test