## "Fossies" - the Fresh Open Source Software Archive

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```    1 /* adler32.c -- compute the Adler-32 checksum of a data stream
3  * For conditions of distribution and use, see copyright notice in zlib.h
4  */
5
6 /* @(#) \$Id\$ */
7
8 #include "zutil.h"
9
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
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 /* ========================================================================= */
65     const Bytef *buf;
66     z_size_t len;
67 hlOpen(67,1);{
68     unsigned long sum2;
69     unsigned n;
70
71     /* split Adler-32 into component sums */
72     sum2 = (adler >> 16) & 0xffff;
74
75     /* in case user likes doing a byte at a time, keep it fast */
76     if (len == 1) hlOpen(76,2);{
81         if (sum2 >= BASE)
82             sum2 -= BASE;
83         return adler | (sum2 << 16);
84     hlClose(2, 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) hlOpen(91,2);{
92         while (len--) hlOpen(92,3);{
95         hlClose(4, 95);}
98         MOD28(sum2);            /* only added so many BASE's */
99         return adler | (sum2 << 16);
100     hlClose(3, 100);}
101
102     /* do length NMAX blocks -- requires just one modulo operation */
103     while (len >= NMAX) hlOpen(103,2);{
104         len -= NMAX;
105         n = NMAX / 16;          /* NMAX is divisible by 16 */
106         do hlOpen(106,3);{
107             DO16(buf);          /* 16 sums unrolled */
108             buf += 16;
109         hlClose(6, 109);} while (--n);
111         MOD(sum2);
112     hlClose(5, 112);}
113
114     /* do remaining bytes (less than NMAX, still just one modulo) */
115     if (len) hlOpen(115,2);{                  /* avoid modulos if none remaining */
116         while (len >= 16) hlOpen(116,3);{
117             len -= 16;
118             DO16(buf);
119             buf += 16;
120         hlClose(8, 120);}
121         while (len--) hlOpen(121,3);{
124         hlClose(9, 124);}
126         MOD(sum2);
127     hlClose(7, 127);}
128
129     /* return recombined sums */
130     return adler | (sum2 << 16);
131 hlClose(1, 131);}
132
133 /* ========================================================================= */
136     const Bytef *buf;
137     uInt len;
138 hlOpen(138,1);{
140 hlClose(10, 140);}
141
142 /* ========================================================================= */
146     z_off64_t len2;
147 hlOpen(147,1);{
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 hlClose(11, 169);}
170
171 /* ========================================================================= */