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/* rollsum.c -- compute the rsync rolling checksum of a data stream
*/
/* @(#) $Id$ */
#include "rollsum.h"
#define DO1(buf,i) {s1 += buf[i]; s2 += s1;}
#define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
#define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
#define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
#define DO16(buf) DO8(buf,0); DO8(buf,8);
#define OF16(off) {s1 += 16*off; s2 += 136*off;}
void RollsumUpdate(Rollsum *sum,const unsigned char *buf,unsigned int len) {
/* ANSI C says no overflow for unsigned.
zlib's adler 32 goes to extra effort to avoid overflow*/
unsigned long s1 = sum->s1;
unsigned long s2 = sum->s2;
sum->count+=len; /* increment sum count */
while (len >= 16) {
DO16(buf);
OF16(ROLLSUM_CHAR_OFFSET);
buf += 16;
len -= 16;
}
while (len != 0) {
s1 += (*buf++ + ROLLSUM_CHAR_OFFSET);
s2 += s1;
len--;
}
sum->s1=s1;
sum->s2=s2;
}
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