1/* adler32_p.h -- Private inline functions and macros shared with
2 * different computation of the Adler-32 checksum
3 * of a data stream.
4 * Copyright (C) 1995-2011, 2016 Mark Adler
5 * For conditions of distribution and use, see copyright notice in zlib.h
6 */
7
8#ifndef ADLER32_P_H
9#define ADLER32_P_H
10
11#define BASE 65521U /* largest prime smaller than 65536 */
12#define NMAX 5552
13/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
14
15/* use NO_DIVIDE if your processor does not do division in hardware --
16 try it both ways to see which is faster */
17#ifdef NO_DIVIDE
18/* note that this assumes BASE is 65521, where 65536 % 65521 == 15
19 (thank you to John Reiser for pointing this out) */
20# define CHOP(a) \
21 do { \
22 uint32_t tmp = a >> 16; \
23 a &= 0xffff; \
24 a += (tmp << 4) - tmp; \
25 } while (0)
26# define MOD28(a) \
27 do { \
28 CHOP(a); \
29 if (a >= BASE) a -= BASE; \
30 } while (0)
31# define MOD(a) \
32 do { \
33 CHOP(a); \
34 MOD28(a); \
35 } while (0)
36# define MOD63(a) \
37 do { /* this assumes a is not negative */ \
38 z_off64_t tmp = a >> 32; \
39 a &= 0xffffffffL; \
40 a += (tmp << 8) - (tmp << 5) + tmp; \
41 tmp = a >> 16; \
42 a &= 0xffffL; \
43 a += (tmp << 4) - tmp; \
44 tmp = a >> 16; \
45 a &= 0xffffL; \
46 a += (tmp << 4) - tmp; \
47 if (a >= BASE) a -= BASE; \
48 } while (0)
49#else
50# define MOD(a) a %= BASE
51# define MOD28(a) a %= BASE
52# define MOD63(a) a %= BASE
53#endif
54
55static inline uint32_t adler32_len_1(uint32_t adler, const unsigned char *buf, uint32_t sum2) {
56 adler += buf[0];
57 if (adler >= BASE)
58 adler -= BASE;
59 sum2 += adler;
60 if (sum2 >= BASE)
61 sum2 -= BASE;
62 return adler | (sum2 << 16);
63}
64
65static inline uint32_t adler32_len_16(uint32_t adler, const unsigned char *buf, size_t len, uint32_t sum2) {
66 while (len) {
67 --len;
68 adler += *buf++;
69 sum2 += adler;
70 }
71 if (adler >= BASE)
72 adler -= BASE;
73 MOD28(sum2); /* only added so many BASE's */
74 return adler | (sum2 << 16);
75}
76
77#endif /* ADLER32_P_H */
78