1 #include <u.h> 2 #include <libc.h> 3 #include <flate.h> 4 5 enum 6 { 7 ADLERITERS = 5552, /* max iters before can overflow 32 bits */ 8 ADLERBASE = 65521 /* largest prime smaller than 65536 */ 9 }; 10 11 ulong adler32(ulong adler,void * vbuf,int n)12adler32(ulong adler, void *vbuf, int n) 13 { 14 ulong s1, s2; 15 uchar *buf, *ebuf; 16 int m; 17 18 buf = vbuf; 19 s1 = adler & 0xffff; 20 s2 = (adler >> 16) & 0xffff; 21 for(; n >= 16; n -= m){ 22 m = n; 23 if(m > ADLERITERS) 24 m = ADLERITERS; 25 m &= ~15; 26 for(ebuf = buf + m; buf < ebuf; buf += 16){ 27 s1 += buf[0]; 28 s2 += s1; 29 s1 += buf[1]; 30 s2 += s1; 31 s1 += buf[2]; 32 s2 += s1; 33 s1 += buf[3]; 34 s2 += s1; 35 s1 += buf[4]; 36 s2 += s1; 37 s1 += buf[5]; 38 s2 += s1; 39 s1 += buf[6]; 40 s2 += s1; 41 s1 += buf[7]; 42 s2 += s1; 43 s1 += buf[8]; 44 s2 += s1; 45 s1 += buf[9]; 46 s2 += s1; 47 s1 += buf[10]; 48 s2 += s1; 49 s1 += buf[11]; 50 s2 += s1; 51 s1 += buf[12]; 52 s2 += s1; 53 s1 += buf[13]; 54 s2 += s1; 55 s1 += buf[14]; 56 s2 += s1; 57 s1 += buf[15]; 58 s2 += s1; 59 } 60 s1 %= ADLERBASE; 61 s2 %= ADLERBASE; 62 } 63 if(n){ 64 for(ebuf = buf + n; buf < ebuf; buf++){ 65 s1 += buf[0]; 66 s2 += s1; 67 } 68 s1 %= ADLERBASE; 69 s2 %= ADLERBASE; 70 } 71 return (s2 << 16) + s1; 72 } 73