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/******************************************************************************
Filename : pagerank.c
Description : Google PageRank Checksum Algorithm
Author : http://zhiwei.li/
Log : Ver 0.1 2005-9-13 first release
Ver 1.0 2005-10-19 fixed :final character bug
Ver 1.1 2006-10-05 refine code
Ver 1.2 2008-8-20 use boolean type
******************************************************************************/
#include <stdio.h>
#include <stdbool.h>
int ConvertStrToInt(char *pStr, int Init, int Factor)
{
while (*pStr) {
Init *= Factor;
Init += *pStr++;
}
return Init;
}
int HashURL(char *pStr)
{
unsigned int C1, C2, T1, T2;
C1 = ConvertStrToInt(pStr, 0x1505, 0x21);
C2 = ConvertStrToInt(pStr, 0, 0x1003F);
C1 >>= 2;
C1 = ((C1 >> 4) & 0x3FFFFC0) | (C1 & 0x3F);
C1 = ((C1 >> 4) & 0x3FFC00) | (C1 & 0x3FF);
C1 = ((C1 >> 4) & 0x3C000) | (C1 & 0x3FFF);
T1 = (C1 & 0x3C0) << 4;
T1 |= C1 & 0x3C;
T1 = (T1 << 2) | (C2 & 0xF0F);
T2 = (C1 & 0xFFFFC000) << 4;
T2 |= C1 & 0x3C00;
T2 = (T2 << 0xA) | (C2 & 0xF0F0000);
return (T1 | T2);
}
char CheckHash(unsigned int HashInt)
{
int Check = 0;
bool Flag = false;
int Remainder;
do {
Remainder = HashInt % 10;
HashInt /= 10;
if (Flag){
Remainder += Remainder;
Remainder = (Remainder / 10) + (Remainder % 10);
}
Check += Remainder;
Flag = !Flag;
} while( 0 != HashInt);
Check %= 10;
if (0 != Check) {
Check = 10 - Check;
if (Flag) {
if (1 == (Check % 2)) {
Check += 9;
}
Check >>= 1;
}
}
Check += 0x30;
return Check;
}
int main(int argc, char* argv[])
{
unsigned int HashInt;
if (argc != 2) {
printf("Usage: %s [URL]\n",argv[0]);
return 1;
}
HashInt = HashURL(argv[1]);
printf("Checksum=7%c%u\n", CheckHash(HashInt), HashInt);
return 0;
}
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