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 local 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 /* ========================================================================= */
adler32_z(adler,buf,len)63 uLong 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 /* ========================================================================= */
adler32(adler,buf,len)134 uLong 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 /* ========================================================================= */
adler32_combine_(adler1,adler2,len2)143 local 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 /* ========================================================================= */
adler32_combine(adler1,adler2,len2)172 uLong 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 
adler32_combine64(adler1,adler2,len2)180 uLong 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