1*4882a593Smuzhiyun /* adler32.c -- compute the Adler-32 checksum of a data stream
2*4882a593Smuzhiyun * Copyright (C) 1995-2004 Mark Adler
3*4882a593Smuzhiyun * For conditions of distribution and use, see copyright notice in zlib.h
4*4882a593Smuzhiyun */
5*4882a593Smuzhiyun
6*4882a593Smuzhiyun /* @(#) $Id$ */
7*4882a593Smuzhiyun
8*4882a593Smuzhiyun #define ZLIB_INTERNAL
9*4882a593Smuzhiyun #include "zlib.h"
10*4882a593Smuzhiyun
11*4882a593Smuzhiyun #define BASE 65521UL /* largest prime smaller than 65536 */
12*4882a593Smuzhiyun #define NMAX 5552
13*4882a593Smuzhiyun /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
14*4882a593Smuzhiyun
15*4882a593Smuzhiyun #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
16*4882a593Smuzhiyun #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
17*4882a593Smuzhiyun #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
18*4882a593Smuzhiyun #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
19*4882a593Smuzhiyun #define DO16(buf) DO8(buf,0); DO8(buf,8);
20*4882a593Smuzhiyun
21*4882a593Smuzhiyun /* use NO_DIVIDE if your processor does not do division in hardware */
22*4882a593Smuzhiyun #ifdef NO_DIVIDE
23*4882a593Smuzhiyun # define MOD(a) \
24*4882a593Smuzhiyun do { \
25*4882a593Smuzhiyun if (a >= (BASE << 16)) a -= (BASE << 16); \
26*4882a593Smuzhiyun if (a >= (BASE << 15)) a -= (BASE << 15); \
27*4882a593Smuzhiyun if (a >= (BASE << 14)) a -= (BASE << 14); \
28*4882a593Smuzhiyun if (a >= (BASE << 13)) a -= (BASE << 13); \
29*4882a593Smuzhiyun if (a >= (BASE << 12)) a -= (BASE << 12); \
30*4882a593Smuzhiyun if (a >= (BASE << 11)) a -= (BASE << 11); \
31*4882a593Smuzhiyun if (a >= (BASE << 10)) a -= (BASE << 10); \
32*4882a593Smuzhiyun if (a >= (BASE << 9)) a -= (BASE << 9); \
33*4882a593Smuzhiyun if (a >= (BASE << 8)) a -= (BASE << 8); \
34*4882a593Smuzhiyun if (a >= (BASE << 7)) a -= (BASE << 7); \
35*4882a593Smuzhiyun if (a >= (BASE << 6)) a -= (BASE << 6); \
36*4882a593Smuzhiyun if (a >= (BASE << 5)) a -= (BASE << 5); \
37*4882a593Smuzhiyun if (a >= (BASE << 4)) a -= (BASE << 4); \
38*4882a593Smuzhiyun if (a >= (BASE << 3)) a -= (BASE << 3); \
39*4882a593Smuzhiyun if (a >= (BASE << 2)) a -= (BASE << 2); \
40*4882a593Smuzhiyun if (a >= (BASE << 1)) a -= (BASE << 1); \
41*4882a593Smuzhiyun if (a >= BASE) a -= BASE; \
42*4882a593Smuzhiyun } while (0)
43*4882a593Smuzhiyun # define MOD4(a) \
44*4882a593Smuzhiyun do { \
45*4882a593Smuzhiyun if (a >= (BASE << 4)) a -= (BASE << 4); \
46*4882a593Smuzhiyun if (a >= (BASE << 3)) a -= (BASE << 3); \
47*4882a593Smuzhiyun if (a >= (BASE << 2)) a -= (BASE << 2); \
48*4882a593Smuzhiyun if (a >= (BASE << 1)) a -= (BASE << 1); \
49*4882a593Smuzhiyun if (a >= BASE) a -= BASE; \
50*4882a593Smuzhiyun } while (0)
51*4882a593Smuzhiyun #else
52*4882a593Smuzhiyun # define MOD(a) a %= BASE
53*4882a593Smuzhiyun # define MOD4(a) a %= BASE
54*4882a593Smuzhiyun #endif
55*4882a593Smuzhiyun
56*4882a593Smuzhiyun /* ========================================================================= */
adler32(uLong adler,const Bytef * buf,uInt len)57*4882a593Smuzhiyun uLong ZEXPORT adler32(uLong adler, const Bytef *buf, uInt len)
58*4882a593Smuzhiyun {
59*4882a593Smuzhiyun unsigned long sum2;
60*4882a593Smuzhiyun unsigned n;
61*4882a593Smuzhiyun
62*4882a593Smuzhiyun /* split Adler-32 into component sums */
63*4882a593Smuzhiyun sum2 = (adler >> 16) & 0xffff;
64*4882a593Smuzhiyun adler &= 0xffff;
65*4882a593Smuzhiyun
66*4882a593Smuzhiyun /* in case user likes doing a byte at a time, keep it fast */
67*4882a593Smuzhiyun if (len == 1) {
68*4882a593Smuzhiyun adler += buf[0];
69*4882a593Smuzhiyun if (adler >= BASE)
70*4882a593Smuzhiyun adler -= BASE;
71*4882a593Smuzhiyun sum2 += adler;
72*4882a593Smuzhiyun if (sum2 >= BASE)
73*4882a593Smuzhiyun sum2 -= BASE;
74*4882a593Smuzhiyun return adler | (sum2 << 16);
75*4882a593Smuzhiyun }
76*4882a593Smuzhiyun
77*4882a593Smuzhiyun /* initial Adler-32 value (deferred check for len == 1 speed) */
78*4882a593Smuzhiyun if (buf == Z_NULL)
79*4882a593Smuzhiyun return 1L;
80*4882a593Smuzhiyun
81*4882a593Smuzhiyun /* in case short lengths are provided, keep it somewhat fast */
82*4882a593Smuzhiyun if (len < 16) {
83*4882a593Smuzhiyun while (len--) {
84*4882a593Smuzhiyun adler += *buf++;
85*4882a593Smuzhiyun sum2 += adler;
86*4882a593Smuzhiyun }
87*4882a593Smuzhiyun if (adler >= BASE)
88*4882a593Smuzhiyun adler -= BASE;
89*4882a593Smuzhiyun MOD4(sum2); /* only added so many BASE's */
90*4882a593Smuzhiyun return adler | (sum2 << 16);
91*4882a593Smuzhiyun }
92*4882a593Smuzhiyun
93*4882a593Smuzhiyun /* do length NMAX blocks -- requires just one modulo operation */
94*4882a593Smuzhiyun while (len >= NMAX) {
95*4882a593Smuzhiyun len -= NMAX;
96*4882a593Smuzhiyun n = NMAX / 16; /* NMAX is divisible by 16 */
97*4882a593Smuzhiyun do {
98*4882a593Smuzhiyun DO16(buf); /* 16 sums unrolled */
99*4882a593Smuzhiyun buf += 16;
100*4882a593Smuzhiyun } while (--n);
101*4882a593Smuzhiyun MOD(adler);
102*4882a593Smuzhiyun MOD(sum2);
103*4882a593Smuzhiyun }
104*4882a593Smuzhiyun
105*4882a593Smuzhiyun /* do remaining bytes (less than NMAX, still just one modulo) */
106*4882a593Smuzhiyun if (len) { /* avoid modulos if none remaining */
107*4882a593Smuzhiyun while (len >= 16) {
108*4882a593Smuzhiyun len -= 16;
109*4882a593Smuzhiyun DO16(buf);
110*4882a593Smuzhiyun buf += 16;
111*4882a593Smuzhiyun }
112*4882a593Smuzhiyun while (len--) {
113*4882a593Smuzhiyun adler += *buf++;
114*4882a593Smuzhiyun sum2 += adler;
115*4882a593Smuzhiyun }
116*4882a593Smuzhiyun MOD(adler);
117*4882a593Smuzhiyun MOD(sum2);
118*4882a593Smuzhiyun }
119*4882a593Smuzhiyun
120*4882a593Smuzhiyun /* return recombined sums */
121*4882a593Smuzhiyun return adler | (sum2 << 16);
122*4882a593Smuzhiyun }
123