Subject: [Tsvwg] CRC-32c Algorithm checking D'oh

From: "Douglas Otis" <[email-masked]>
Date: Wed, 20 Jun 2001 19:00:49 -0700

All,

I have made an error in the CRC algorithm presented in the SCTP digest
draft.  The reflected table returns a value that has MS and LS bytes
reflected in addition to the bits within a byte.  The error was my placement
of the results.

There is an example code that implements both the table methods and a bit by
bit method for comparison.  Here is the results with a test pattern of
"123456789".

Table CRC results: Normalized =C14960C7  Reflected =E3069283
Table CRC check: Normalized =FFFFFFFF  Reflected =FFFFFFFF
Bit CRC results: Normal =C14960C7

Doug

#define polynomial 0x1EDC6F41L

/* generated using (0x11EDC6F41)

   x^32+x^28+x^27+x^26+x^25+x^23+x^22+x^20+x^19+x^18+x^14+x^13+
   x^11+x^10+x^9+x^8+x^6+1

 */

unsigned long crctab[256] =
{
  0x00000000L, 0xF26B8303L, 0xE13B70F7L, 0x1350F3F4L,
  0xC79A971FL, 0x35F1141CL, 0x26A1E7E8L, 0xD4CA64EBL,
  0x8AD958CFL, 0x78B2DBCCL, 0x6BE22838L, 0x9989AB3BL,
  0x4D43CFD0L, 0xBF284CD3L, 0xAC78BF27L, 0x5E133C24L,
  0x105EC76FL, 0xE235446CL, 0xF165B798L, 0x030E349BL,
  0xD7C45070L, 0x25AFD373L, 0x36FF2087L, 0xC494A384L,
  0x9A879FA0L, 0x68EC1CA3L, 0x7BBCEF57L, 0x89D76C54L,
  0x5D1D08BFL, 0xAF768BBCL, 0xBC267848L, 0x4E4DFB4BL,
  0x20BD8EDEL, 0xD2D60DDDL, 0xC186FE29L, 0x33ED7D2AL,
  0xE72719C1L, 0x154C9AC2L, 0x061C6936L, 0xF477EA35L,
  0xAA64D611L, 0x580F5512L, 0x4B5FA6E6L, 0xB93425E5L,
  0x6DFE410EL, 0x9F95C20DL, 0x8CC531F9L, 0x7EAEB2FAL,
  0x30E349B1L, 0xC288CAB2L, 0xD1D83946L, 0x23B3BA45L,
  0xF779DEAEL, 0x05125DADL, 0x1642AE59L, 0xE4292D5AL,
  0xBA3A117EL, 0x4851927DL, 0x5B016189L, 0xA96AE28AL,
  0x7DA08661L, 0x8FCB0562L, 0x9C9BF696L, 0x6EF07595L,
  0x417B1DBCL, 0xB3109EBFL, 0xA0406D4BL, 0x522BEE48L,
  0x86E18AA3L, 0x748A09A0L, 0x67DAFA54L, 0x95B17957L,
  0xCBA24573L, 0x39C9C670L, 0x2A993584L, 0xD8F2B687L,
  0x0C38D26CL, 0xFE53516FL, 0xED03A29BL, 0x1F682198L,
  0x5125DAD3L, 0xA34E59D0L, 0xB01EAA24L, 0x42752927L,
  0x96BF4DCCL, 0x64D4CECFL, 0x77843D3BL, 0x85EFBE38L,
  0xDBFC821CL, 0x2997011FL, 0x3AC7F2EBL, 0xC8AC71E8L,
  0x1C661503L, 0xEE0D9600L, 0xFD5D65F4L, 0x0F36E6F7L,
  0x61C69362L, 0x93AD1061L, 0x80FDE395L, 0x72966096L,
  0xA65C047DL, 0x5437877EL, 0x4767748AL, 0xB50CF789L,
  0xEB1FCBADL, 0x197448AEL, 0x0A24BB5AL, 0xF84F3859L,
  0x2C855CB2L, 0xDEEEDFB1L, 0xCDBE2C45L, 0x3FD5AF46L,
  0x7198540DL, 0x83F3D70EL, 0x90A324FAL, 0x62C8A7F9L,
  0xB602C312L, 0x44694011L, 0x5739B3E5L, 0xA55230E6L,
  0xFB410CC2L, 0x092A8FC1L, 0x1A7A7C35L, 0xE811FF36L,
  0x3CDB9BDDL, 0xCEB018DEL, 0xDDE0EB2AL, 0x2F8B6829L,
  0x82F63B78L, 0x709DB87BL, 0x63CD4B8FL, 0x91A6C88CL,
  0x456CAC67L, 0xB7072F64L, 0xA457DC90L, 0x563C5F93L,
  0x082F63B7L, 0xFA44E0B4L, 0xE9141340L, 0x1B7F9043L,
  0xCFB5F4A8L, 0x3DDE77ABL, 0x2E8E845FL, 0xDCE5075CL,
  0x92A8FC17L, 0x60C37F14L, 0x73938CE0L, 0x81F80FE3L,
  0x55326B08L, 0xA759E80BL, 0xB4091BFFL, 0x466298FCL,
  0x1871A4D8L, 0xEA1A27DBL, 0xF94AD42FL, 0x0B21572CL,
  0xDFEB33C7L, 0x2D80B0C4L, 0x3ED04330L, 0xCCBBC033L,
  0xA24BB5A6L, 0x502036A5L, 0x4370C551L, 0xB11B4652L,
  0x65D122B9L, 0x97BAA1BAL, 0x84EA524EL, 0x7681D14DL,
  0x2892ED69L, 0xDAF96E6AL, 0xC9A99D9EL, 0x3BC21E9DL,
  0xEF087A76L, 0x1D63F975L, 0x0E330A81L, 0xFC588982L,
  0xB21572C9L, 0x407EF1CAL, 0x532E023EL, 0xA145813DL,
  0x758FE5D6L, 0x87E466D5L, 0x94B49521L, 0x66DF1622L,
  0x38CC2A06L, 0xCAA7A905L, 0xD9F75AF1L, 0x2B9CD9F2L,
  0xFF56BD19L, 0x0D3D3E1AL, 0x1E6DCDEEL, 0xEC064EEDL,
  0xC38D26C4L, 0x31E6A5C7L, 0x22B65633L, 0xD0DDD530L,
  0x0417B1DBL, 0xF67C32D8L, 0xE52CC12CL, 0x1747422FL,
  0x49547E0BL, 0xBB3FFD08L, 0xA86F0EFCL, 0x5A048DFFL,
  0x8ECEE914L, 0x7CA56A17L, 0x6FF599E3L, 0x9D9E1AE0L,
  0xD3D3E1ABL, 0x21B862A8L, 0x32E8915CL, 0xC083125FL,
  0x144976B4L, 0xE622F5B7L, 0xF5720643L, 0x07198540L,
  0x590AB964L, 0xAB613A67L, 0xB831C993L, 0x4A5A4A90L,
  0x9E902E7BL, 0x6CFBAD78L, 0x7FAB5E8CL, 0x8DC0DD8FL,
  0xE330A81AL, 0x115B2B19L, 0x020BD8EDL, 0xF0605BEEL,
  0x24AA3F05L, 0xD6C1BC06L, 0xC5914FF2L, 0x37FACCF1L,
  0x69E9F0D5L, 0x9B8273D6L, 0x88D28022L, 0x7AB90321L,
  0xAE7367CAL, 0x5C18E4C9L, 0x4F48173DL, 0xBD23943EL,
  0xF36E6F75L, 0x0105EC76L, 0x12551F82L, 0xE03E9C81L,
  0x34F4F86AL, 0xC69F7B69L, 0xD5CF889DL, 0x27A40B9EL,
  0x79B737BAL, 0x8BDCB4B9L, 0x988C474DL, 0x6AE7C44EL,
  0xBE2DA0A5L, 0x4C4623A6L, 0x5F16D052L, 0xAD7D5351L
};

#define CRC32(crc, d) (crc=(crc>>8)^crctab[(crc^(d))&0xff])

unsigned char testbuf[] =
{
  0x31,
  0x32,
  0x33,
  0x34,
  0x35,
  0x36,
  0x37,
  0x38,
  0x39,
  0x00,
  0x00,
  0x00,
  0x00,
};

unsigned int
  rb (unsigned int r)

{
  int i;
  unsigned int n = r;

  for (i = 0; i < 8; i++)
    {
      if (n & 1)
	r |= 1 << (7 - i);
      else
	r &= ~(1 << (7 - i));
      n >>= 1;
    }
  return r;
}

/* fscgen generates the digest based on Digest Designator */
/* buf[] contains the SCTP packet                         */
/* length is the packet length including padding          */

unsigned int
  tablegen (unsigned char buf[], int length)
{
  int i = 0;
  unsigned int crc = ~0;

  while (i < length)
    {
      CRC32 (crc, buf[i++]);	/* assumes digest zeroed */
    }
  crc ^= ~0;
  return (crc);
}

unsigned int
  bitgen (unsigned char buf[], int length)
{
  int i = 0;
  int j;
  unsigned char d;
  unsigned int crc = ~0;

  while (i < length)
    {
      d = buf[i++];
      for (j = 0; j < 8; j++)
	{
	  if ((crc >> 31) ^ (d & 1))
	    {
	      crc = (crc << 1) ^ polynomial;
	    }
	  else
	    {
	      crc <<= 1;
	    }
	  d >>= 1;
	}
    }
  crc ^= ~0;

  return (crc);
}

main ()
{
  unsigned int val;

  val = tablegen (testbuf, 9);

  printf ("Table CRC results: Normalized =%02X%02X%02X%02X  Reflected
=%X\n",
	  rb (val & 0xff),
	  rb ((val >> 8) & 0xff),
	  rb ((val >> 16) & 0xff),
	  rb (val >> 24),
	  val);

  val ^= ~0;
  testbuf[9] = val & 0xff;
  testbuf[10] = (val >> 8) & 0xff;
  testbuf[11] = (val >> 16) & 0xff;
  testbuf[12] = (val >> 24) & 0xff;

  val = tablegen (testbuf, 13);

  printf ("Table CRC check: Normalized =%02X%02X%02X%02X  Reflected =%X\n",
	  rb (val & 0xff),
	  rb ((val >> 8) & 0xff),
	  rb ((val >> 16) & 0xff),
	  rb (val >> 24),
	  val);

  val = bitgen (testbuf, 9);
  printf ("Bit CRC results: Normal =%X\n", val);
}

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