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
10local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2));
11
12#define BASE 65521U     /* largest prime smaller than 65536 */
13#define NMAX 5552
14/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
15
16#define DO1(buf,i)  {adler += (buf)[i]; sum2 += adler;}
17#define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
18#define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
19#define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
20#define DO16(buf)   DO8(buf,0); DO8(buf,8);
21
22/* use NO_DIVIDE if your processor does not do division in hardware --
23   try it both ways to see which is faster */
24#ifdef NO_DIVIDE
25/* note that this assumes BASE is 65521, where 65536 % 65521 == 15
26   (thank you to John Reiser for pointing this out) */
27#  define CHOP(a) \
28    do { \
29        unsigned long tmp = a >> 16; \
30        a &= 0xffffUL; \
31        a += (tmp << 4) - tmp; \
32    } while (0)
33#  define MOD28(a) \
34    do { \
35        CHOP(a); \
36        if (a >= BASE) a -= BASE; \
37    } while (0)
38#  define MOD(a) \
39    do { \
40        CHOP(a); \
41        MOD28(a); \
42    } while (0)
43#  define MOD63(a) \
44    do { /* this assumes a is not negative */ \
45        z_off64_t tmp = a >> 32; \
46        a &= 0xffffffffL; \
47        a += (tmp << 8) - (tmp << 5) + tmp; \
48        tmp = a >> 16; \
49        a &= 0xffffL; \
50        a += (tmp << 4) - tmp; \
51        tmp = a >> 16; \
52        a &= 0xffffL; \
53        a += (tmp << 4) - tmp; \
54        if (a >= BASE) a -= BASE; \
55    } while (0)
56#else
57#  define MOD(a) a %= BASE
58#  define MOD28(a) a %= BASE
59#  define MOD63(a) a %= BASE
60#endif
61
62/* ========================================================================= */
63uLong ZEXPORT adler32_z(adler, buf, len)
64    uLong adler;
65    const Bytef *buf;
66    z_size_t len;
67{
68    unsigned long sum2;
69    unsigned n;
70
71    /* split Adler-32 into component sums */
72    sum2 = (adler >> 16) & 0xffff;
73    adler &= 0xffff;
74
75    /* in case user likes doing a byte at a time, keep it fast */
76    if (len == 1) {
77        adler += buf[0];
78        if (adler >= BASE)
79            adler -= BASE;
80        sum2 += adler;
81        if (sum2 >= BASE)
82            sum2 -= BASE;
83        return adler | (sum2 << 16);
84    }
85
86    /* initial Adler-32 value (deferred check for len == 1 speed) */
87    if (buf == Z_NULL)
88        return 1L;
89
90    /* in case short lengths are provided, keep it somewhat fast */
91    if (len < 16) {
92        while (len--) {
93            adler += *buf++;
94            sum2 += adler;
95        }
96        if (adler >= BASE)
97            adler -= BASE;
98        MOD28(sum2);            /* only added so many BASE's */
99        return adler | (sum2 << 16);
100    }
101
102    /* do length NMAX blocks -- requires just one modulo operation */
103    while (len >= NMAX) {
104        len -= NMAX;
105        n = NMAX / 16;          /* NMAX is divisible by 16 */
106        do {
107            DO16(buf);          /* 16 sums unrolled */
108            buf += 16;
109        } while (--n);
110        MOD(adler);
111        MOD(sum2);
112    }
113
114    /* do remaining bytes (less than NMAX, still just one modulo) */
115    if (len) {                  /* avoid modulos if none remaining */
116        while (len >= 16) {
117            len -= 16;
118            DO16(buf);
119            buf += 16;
120        }
121        while (len--) {
122            adler += *buf++;
123            sum2 += adler;
124        }
125        MOD(adler);
126        MOD(sum2);
127    }
128
129    /* return recombined sums */
130    return adler | (sum2 << 16);
131}
132
133/* ========================================================================= */
134uLong ZEXPORT adler32(adler, buf, len)
135    uLong adler;
136    const Bytef *buf;
137    uInt len;
138{
139    return adler32_z(adler, buf, len);
140}
141
142/* ========================================================================= */
143local uLong adler32_combine_(adler1, adler2, len2)
144    uLong adler1;
145    uLong adler2;
146    z_off64_t len2;
147{
148    unsigned long sum1;
149    unsigned long sum2;
150    unsigned rem;
151
152    /* for negative len, return invalid adler32 as a clue for debugging */
153    if (len2 < 0)
154        return 0xffffffffUL;
155
156    /* the derivation of this formula is left as an exercise for the reader */
157    MOD63(len2);                /* assumes len2 >= 0 */
158    rem = (unsigned)len2;
159    sum1 = adler1 & 0xffff;
160    sum2 = rem * sum1;
161    MOD(sum2);
162    sum1 += (adler2 & 0xffff) + BASE - 1;
163    sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
164    if (sum1 >= BASE) sum1 -= BASE;
165    if (sum1 >= BASE) sum1 -= BASE;
166    if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1);
167    if (sum2 >= BASE) sum2 -= BASE;
168    return sum1 | (sum2 << 16);
169}
170
171/* ========================================================================= */
172uLong ZEXPORT adler32_combine(adler1, adler2, len2)
173    uLong adler1;
174    uLong adler2;
175    z_off_t len2;
176{
177    return adler32_combine_(adler1, adler2, len2);
178}
179
180uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
181    uLong adler1;
182    uLong adler2;
183    z_off64_t len2;
184{
185    return adler32_combine_(adler1, adler2, len2);
186}
187