1 // SPDX-License-Identifier: Zlib
2 /* adler32.c -- compute the Adler-32 checksum of a data stream
3  * Copyright (C) 1995-2011, 2016 Mark Adler
4  * For conditions of distribution and use, see copyright notice in zlib.h
5  */
6 
7 /* @(#) $Id$ */
8 
9 #include "zutil.h"
10 
11 local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2));
12 
13 #define BASE 65521U     /* largest prime smaller than 65536 */
14 #define NMAX 5552
15 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
16 
17 #define DO1(buf,i)  {adler += (buf)[i]; sum2 += adler;}
18 #define DO2(buf,i)  DO1(buf,i); DO1(buf,i+1);
19 #define DO4(buf,i)  DO2(buf,i); DO2(buf,i+2);
20 #define DO8(buf,i)  DO4(buf,i); DO4(buf,i+4);
21 #define DO16(buf)   DO8(buf,0); DO8(buf,8);
22 
23 /* use NO_DIVIDE if your processor does not do division in hardware --
24    try it both ways to see which is faster */
25 #ifdef NO_DIVIDE
26 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15
27    (thank you to John Reiser for pointing this out) */
28 #  define CHOP(a) \
29     do { \
30         unsigned long tmp = a >> 16; \
31         a &= 0xffffUL; \
32         a += (tmp << 4) - tmp; \
33     } while (0)
34 #  define MOD28(a) \
35     do { \
36         CHOP(a); \
37         if (a >= BASE) a -= BASE; \
38     } while (0)
39 #  define MOD(a) \
40     do { \
41         CHOP(a); \
42         MOD28(a); \
43     } while (0)
44 #  define MOD63(a) \
45     do { /* this assumes a is not negative */ \
46         z_off64_t tmp = a >> 32; \
47         a &= 0xffffffffL; \
48         a += (tmp << 8) - (tmp << 5) + tmp; \
49         tmp = a >> 16; \
50         a &= 0xffffL; \
51         a += (tmp << 4) - tmp; \
52         tmp = a >> 16; \
53         a &= 0xffffL; \
54         a += (tmp << 4) - tmp; \
55         if (a >= BASE) a -= BASE; \
56     } while (0)
57 #else
58 #  define MOD(a) a %= BASE
59 #  define MOD28(a) a %= BASE
60 #  define MOD63(a) a %= BASE
61 #endif
62 
63 /* ========================================================================= */
adler32_z(adler,buf,len)64 uLong ZEXPORT adler32_z(adler, buf, len)
65     uLong adler;
66     const Bytef *buf;
67     z_size_t len;
68 {
69     unsigned long sum2;
70     unsigned n;
71 
72     /* split Adler-32 into component sums */
73     sum2 = (adler >> 16) & 0xffff;
74     adler &= 0xffff;
75 
76     /* in case user likes doing a byte at a time, keep it fast */
77     if (len == 1) {
78         adler += buf[0];
79         if (adler >= BASE)
80             adler -= BASE;
81         sum2 += adler;
82         if (sum2 >= BASE)
83             sum2 -= BASE;
84         return adler | (sum2 << 16);
85     }
86 
87     /* initial Adler-32 value (deferred check for len == 1 speed) */
88     if (buf == Z_NULL)
89         return 1L;
90 
91     /* in case short lengths are provided, keep it somewhat fast */
92     if (len < 16) {
93         while (len--) {
94             adler += *buf++;
95             sum2 += adler;
96         }
97         if (adler >= BASE)
98             adler -= BASE;
99         MOD28(sum2);            /* only added so many BASE's */
100         return adler | (sum2 << 16);
101     }
102 
103     /* do length NMAX blocks -- requires just one modulo operation */
104     while (len >= NMAX) {
105         len -= NMAX;
106         n = NMAX / 16;          /* NMAX is divisible by 16 */
107         do {
108             DO16(buf);          /* 16 sums unrolled */
109             buf += 16;
110         } while (--n);
111         MOD(adler);
112         MOD(sum2);
113     }
114 
115     /* do remaining bytes (less than NMAX, still just one modulo) */
116     if (len) {                  /* avoid modulos if none remaining */
117         while (len >= 16) {
118             len -= 16;
119             DO16(buf);
120             buf += 16;
121         }
122         while (len--) {
123             adler += *buf++;
124             sum2 += adler;
125         }
126         MOD(adler);
127         MOD(sum2);
128     }
129 
130     /* return recombined sums */
131     return adler | (sum2 << 16);
132 }
133 
134 /* ========================================================================= */
adler32(adler,buf,len)135 uLong ZEXPORT adler32(adler, buf, len)
136     uLong adler;
137     const Bytef *buf;
138     uInt len;
139 {
140     return adler32_z(adler, buf, len);
141 }
142 
143 /* ========================================================================= */
adler32_combine_(adler1,adler2,len2)144 local uLong adler32_combine_(adler1, adler2, len2)
145     uLong adler1;
146     uLong adler2;
147     z_off64_t len2;
148 {
149     unsigned long sum1;
150     unsigned long sum2;
151     unsigned rem;
152 
153     /* for negative len, return invalid adler32 as a clue for debugging */
154     if (len2 < 0)
155         return 0xffffffffUL;
156 
157     /* the derivation of this formula is left as an exercise for the reader */
158     MOD63(len2);                /* assumes len2 >= 0 */
159     rem = (unsigned)len2;
160     sum1 = adler1 & 0xffff;
161     sum2 = rem * sum1;
162     MOD(sum2);
163     sum1 += (adler2 & 0xffff) + BASE - 1;
164     sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
165     if (sum1 >= BASE) sum1 -= BASE;
166     if (sum1 >= BASE) sum1 -= BASE;
167     if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1);
168     if (sum2 >= BASE) sum2 -= BASE;
169     return sum1 | (sum2 << 16);
170 }
171 
172 /* ========================================================================= */
adler32_combine(adler1,adler2,len2)173 uLong ZEXPORT adler32_combine(adler1, adler2, len2)
174     uLong adler1;
175     uLong adler2;
176     z_off_t len2;
177 {
178     return adler32_combine_(adler1, adler2, len2);
179 }
180 
adler32_combine64(adler1,adler2,len2)181 uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
182     uLong adler1;
183     uLong adler2;
184     z_off64_t len2;
185 {
186     return adler32_combine_(adler1, adler2, len2);
187 }
188