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  1.  
  2. #include <stdio.h>
  3. #include <string.h>
  4.  
  5. typedef unsigned int uint;
  6. typedef unsigned char byte;
  7.  
  8. void init_crc32( void );
  9. void init_crc32_merge( void );
  10. uint crc32_merge( uint crc1, uint crc2, uint len2 );
  11.  
  12. uint crc32_update( uint x, byte c );
  13. uint strcrc( char* s ) { uint x; for( x=0; *s++; x=crc32_update(x,s[-1]) ); return x; }
  14.  
  15. int main( void ) {
  16.   init_crc32();
  17.   init_crc32_merge();
  18.  
  19.   char str1[] = "Hello";
  20.   char str2[] = " World!!!";
  21.   char str3[256] = "";
  22.   strcat(str3,str1);
  23.   strcat(str3,str2);
  24.  
  25.   uint c1 = strcrc(str1), l1 = strlen(str1);
  26.   uint c2 = strcrc(str2), l2 = strlen(str2);
  27.   uint c3 = strcrc(str3), l3 = strlen(str3);
  28.  
  29.   printf( "CRC32('%s')=%08X\n", str1, c1 );
  30.   printf( "CRC32('%s')=%08X\n", str2, c2 );
  31.   printf( "CRC32('%s')=%08X\n", str3, c3 );
  32.  
  33.   printf( "crc32_merge(%08X,%08X,%i)=%08X\n", c1,c2,l2, crc32_merge(c1,c2,l2) );
  34.  
  35. }
  36.  
  37. uint CRCTab[256];
  38.  
  39. void init_crc32( void ) {
  40.   uint i, j, c;
  41.   for( i=0; i<256; i++ ) {
  42.     for( c=i,j=0; j<8; j++ ) c=(c&1) ? (c>>1)^0xEDB88320L : (c>>1);
  43.     CRCTab[i^0xFF] = c ^ 0xFF000000;
  44.   }
  45. }
  46.  
  47. uint crc32_update( uint x, byte c ) { return CRCTab[byte(x)^c] ^ (x>>8); }
  48.  
  49. enum{ CRC_LEN=32 };
  50.  
  51. uint crc_mul( uint crc, uint (&mat)[CRC_LEN] ) {
  52.   uint i, out=0;
  53. //  for( i=0; i<32; i++ ) if( crc&(1<<i) ) out ^= mat[i];
  54.   for( i=0; crc; i++,crc>>=1 ) if( crc&1 ) out ^= mat[i];
  55.   return out;
  56. }
  57.  
  58. void crc_set( uint (&out)[CRC_LEN], uint (&inp)[CRC_LEN] ) {
  59.   for( uint i=0; i<CRC_LEN; i++ ) out[i]=inp[i];
  60. }
  61.  
  62. void crc_sqr( uint (&mat)[CRC_LEN] ) {
  63.   uint i, square[CRC_LEN];
  64.   for( i=0; i<CRC_LEN; i++ ) square[i] = crc_mul( mat[i], mat );
  65.   crc_set( mat, square );
  66. }
  67.  
  68. uint crc_pad[CRC_LEN][CRC_LEN];
  69.  
  70. void init_crc32_merge( void ) {
  71.   uint i,mat[CRC_LEN];
  72.   // matrix for adding 1 zero bit to crc
  73.   mat[0] = 0xEDB88320; // CRC32 polynomial
  74.   for( i=1; i<CRC_LEN; i++ ) mat[i] = 1<<(i-1);
  75.   crc_sqr(mat); // 2 bits
  76.   crc_sqr(mat); // 4 bits
  77.   crc_sqr(mat); // 8 bits
  78.   for( i=0; i<CRC_LEN; i++ ) crc_set(crc_pad[i],mat), crc_sqr(mat);
  79. }
  80.  
  81. uint crc32_merge( uint crc1, uint crc2, uint len2 ) {
  82. //  for( uint i=0; i<CRC_LEN; i++ ) if( len2 & (1<<i) ) crc1=crc_mul(crc1,crc_pad[i]);
  83.   for( uint i=0; len2; i++,len2>>=1 ) if( len2&1 ) crc1=crc_mul(crc1,crc_pad[i]);
  84.   return crc1 ^ crc2;
  85. }
  86.  
  87.  
  88.  
Success #stdin #stdout 0s 3472KB
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stdin
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Standard input is empty
stdout
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CRC32('Hello')=F7D18982
CRC32(' World!!!')=11F02F66
CRC32('Hello World!!!')=1004B80E
crc32_merge(F7D18982,11F02F66,9)=1004B80E
https://ideone.com/RQdDKy
language:
C++ (gcc 8.3)
created:
7 years ago
visibility:
public

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