1/* adler32.c -- compute the Adler-32 checksum of a data stream
2 * Copyright (C) 1995-2011, 2016 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
4 */
5
6/* @(#) $Id$ */
7
8#include "zutil.h"
9
10#define BASE 65521U     /* largest prime smaller than 65536 */
11#define NMAX 5552
12/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
13
14#define DO1(buf,i)  {adler += (buf)[i]; sum2 += adler;}
15#define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
16#define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
17#define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
18#define DO16(buf)   DO8(buf,0); DO8(buf,8);
19
20/* use NO_DIVIDE if your processor does not do division in hardware --
21   try it both ways to see which is faster */
22#ifdef NO_DIVIDE
23/* note that this assumes BASE is 65521, where 65536 % 65521 == 15
24   (thank you to John Reiser for pointing this out) */
25#  define CHOP(a) \
26    do { \
27        unsigned long tmp = a >> 16; \
28        a &= 0xffffUL; \
29        a += (tmp << 4) - tmp; \
30    } while (0)
31#  define MOD28(a) \
32    do { \
33        CHOP(a); \
34        if (a >= BASE) a -= BASE; \
35    } while (0)
36#  define MOD(a) \
37    do { \
38        CHOP(a); \
39        MOD28(a); \
40    } while (0)
41#  define MOD63(a) \
42    do { /* this assumes a is not negative */ \
43        z_off64_t tmp = a >> 32; \
44        a &= 0xffffffffL; \
45        a += (tmp << 8) - (tmp << 5) + tmp; \
46        tmp = a >> 16; \
47        a &= 0xffffL; \
48        a += (tmp << 4) - tmp; \
49        tmp = a >> 16; \
50        a &= 0xffffL; \
51        a += (tmp << 4) - tmp; \
52        if (a >= BASE) a -= BASE; \
53    } while (0)
54#else
55#  define MOD(a) a %= BASE
56#  define MOD28(a) a %= BASE
57#  define MOD63(a) a %= BASE
58#endif
59
60/* ========================================================================= */
61uLong ZEXPORT adler32_z(uLong adler, const Bytef *buf, z_size_t len) {
62    unsigned long sum2;
63    unsigned n;
64
65    /* split Adler-32 into component sums */
66    sum2 = (adler >> 16) & 0xffff;
67    adler &= 0xffff;
68
69    /* in case user likes doing a byte at a time, keep it fast */
70    if (len == 1) {
71        adler += buf[0];
72        if (adler >= BASE)
73            adler -= BASE;
74        sum2 += adler;
75        if (sum2 >= BASE)
76            sum2 -= BASE;
77        return adler | (sum2 << 16);
78    }
79
80    /* initial Adler-32 value (deferred check for len == 1 speed) */
81    if (buf == Z_NULL)
82        return 1L;
83
84    /* in case short lengths are provided, keep it somewhat fast */
85    if (len < 16) {
86        while (len--) {
87            adler += *buf++;
88            sum2 += adler;
89        }
90        if (adler >= BASE)
91            adler -= BASE;
92        MOD28(sum2);            /* only added so many BASE's */
93        return adler | (sum2 << 16);
94    }
95
96    /* do length NMAX blocks -- requires just one modulo operation */
97    while (len >= NMAX) {
98        len -= NMAX;
99        n = NMAX / 16;          /* NMAX is divisible by 16 */
100        do {
101            DO16(buf);          /* 16 sums unrolled */
102            buf += 16;
103        } while (--n);
104        MOD(adler);
105        MOD(sum2);
106    }
107
108    /* do remaining bytes (less than NMAX, still just one modulo) */
109    if (len) {                  /* avoid modulos if none remaining */
110        while (len >= 16) {
111            len -= 16;
112            DO16(buf);
113            buf += 16;
114        }
115        while (len--) {
116            adler += *buf++;
117            sum2 += adler;
118        }
119        MOD(adler);
120        MOD(sum2);
121    }
122
123    /* return recombined sums */
124    return adler | (sum2 << 16);
125}
126
127/* ========================================================================= */
128uLong ZEXPORT adler32(uLong adler, const Bytef *buf, uInt len) {
129    return adler32_z(adler, buf, len);
130}
131
132/* ========================================================================= */
133local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2) {
134    unsigned long sum1;
135    unsigned long sum2;
136    unsigned rem;
137
138    /* for negative len, return invalid adler32 as a clue for debugging */
139    if (len2 < 0)
140        return 0xffffffffUL;
141
142    /* the derivation of this formula is left as an exercise for the reader */
143    MOD63(len2);                /* assumes len2 >= 0 */
144    rem = (unsigned)len2;
145    sum1 = adler1 & 0xffff;
146    sum2 = rem * sum1;
147    MOD(sum2);
148    sum1 += (adler2 & 0xffff) + BASE - 1;
149    sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
150    if (sum1 >= BASE) sum1 -= BASE;
151    if (sum1 >= BASE) sum1 -= BASE;
152    if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1);
153    if (sum2 >= BASE) sum2 -= BASE;
154    return sum1 | (sum2 << 16);
155}
156
157/* ========================================================================= */
158uLong ZEXPORT adler32_combine(uLong adler1, uLong adler2, z_off_t len2) {
159    return adler32_combine_(adler1, adler2, len2);
160}
161
162uLong ZEXPORT adler32_combine64(uLong adler1, uLong adler2, z_off64_t len2) {
163    return adler32_combine_(adler1, adler2, len2);
164}
165