Different results using the crc32 function between C# and php

Question

I have been preparing a big list of words using crc32 for hashing each word, I do this process on C# but there is a process on php, my surprise comes when I see that the crc32 function used in C# produces different hash than the standard crc32 function on PHP.

The function on C# gives an unsigned int and php gives signed int but doing printf("%u\n", $crc_value) you can obtaind the usigned int, however this neither match the C# value.

(I put on the bottom the C# code)

Is there a way to ajust the php function for give me the same results?

I put here hashes produces in each language:

php:

$value = crc32("emisiones")
//signed int => 1277409361 
//unsigned int => 1277409361

c#:

Crc32.CRC32String("emisiones");
// unsigned int => 3523227667

Crc32.CRC32Bytes(System.Text.Encoding.ASCII.GetBytes("emisiones"));
// bytes => 101,109,105,115,105,111,110,101,115
// unsigned int => 3525485962

crc32 implementation of c#:

using System;
using System.IO;

namespace Foo
{
    /// <summary>
    /// A utility class to compute CRC32.
    /// </summary>
    public class Crc32
    {
        private uint _crc32 = 0;
        static private uint[] crc_32_tab =  // CRC polynomial 0xedb88320 
          {
        0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f,
        0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
        0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2,
        0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
        0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
        0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
        0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa, 0x42b2986c,
        0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
        0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423,
        0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
        0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 0x01db7106,
        0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
        0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d,
        0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
        0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
        0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
        0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7,
        0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
        0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa,
        0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
        0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81,
        0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
        0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84,
        0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
        0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
        0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
        0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8, 0xa1d1937e,
        0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
        0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55,
        0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
        0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28,
        0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
        0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f,
        0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
        0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
        0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
        0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69,
        0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
        0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc,
        0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
        0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693,
        0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
        0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
      };

        static private uint UPDC32(byte octet, uint crc)
        {
            return (crc_32_tab[((crc) ^ ((byte)octet)) & 0xff] ^ ((crc) >> 8));
        }

        internal uint CheckSum
        {
            get
            {
                return _crc32;
            }
            set
            {
                _crc32 = value;
            }
        }

        internal uint AddToCRC32(int c)
        {
            return AddToCRC32((ushort)c);
        }

        internal uint AddToCRC32(ushort c)
        {
            byte lowByte, hiByte;
            lowByte = (byte)(c & 0x00ff);
            hiByte = (byte)(c >> 8);
            _crc32 = UPDC32(hiByte, _crc32);
            _crc32 = UPDC32(lowByte, _crc32);
            return ~_crc32;
        }

        /// <summary>
        /// Compute a checksum for a given string.
        /// </summary>
        /// <param name="text">The string to compute the checksum for.</param>
        /// <returns>The computed checksum.</returns>
        static public uint CRC32String(string text)
        {
            uint oldcrc32;
            oldcrc32 = 0xFFFFFFFF;
            int len = text.Length;
            ushort uCharVal;
            byte lowByte, hiByte;

            for (int i = 0; len > 0; i++)
            {
                --len;
                uCharVal = text[len];
                unchecked
                {
                    lowByte = (byte)(uCharVal & 0x00ff);
                    hiByte = (byte)(uCharVal >> 8);
                }
                oldcrc32 = UPDC32(hiByte, oldcrc32);
                oldcrc32 = UPDC32(lowByte, oldcrc32);
            }

            return ~oldcrc32;
        }

        /// <summary>
        /// Compute a checksum for a given array of bytes.
        /// </summary>
        /// <param name="bytes">The array of bytes to compute the checksum for.</param>
        /// <returns>The computed checksum.</returns>
        static public uint CRC32Bytes(byte[] bytes)
        {
            uint oldcrc32;
            oldcrc32 = 0xFFFFFFFF;
            int len = bytes.Length;

            for (int i = 0; len > 0; i++)
            {
                --len;
                oldcrc32 = UPDC32(bytes[len], oldcrc32);
            }
            return ~oldcrc32;
        }
    }
}

Answer 1

CRC32String() is running two bytes per character through. If you are expecting one byte per character, as the PHP code would, then you should use CRC32Bytes().

Having done that, you need to fix both of those routines. They are computing the CRC on the reverse of the string. (Who wrote those routines?) If you run CRC32Bytes() on "senoisime", then you will get 1277409361. And if you run php's crc32() on "senoisime", you will get 3525485962.

CRC32String() and CRC32Bytes() use text[len] and bytes[len] when they should be using text[i] and bytes[i]. i counts forward, but len counts backwards. This is clearly just someone's brain fart, since you wouldn't even need the variable i if you actually intended to compute the CRC on the reverse of the string.

Also it's a rather odd way to write the code in the first place. They should have just used the most common C-ish idiom instead: for (i = 0; i < len; i++).