xref: /third_party/ffmpeg/libavutil/adler32.c (revision cabdff1a) 
1/*
2 * Compute the Adler-32 checksum of a data stream.
3 * This is a modified version based on adler32.c from the zlib library.
4 *
5 * Copyright (C) 1995 Mark Adler
6 *
7 * This software is provided 'as-is', without any express or implied
8 * warranty.  In no event will the authors be held liable for any damages
9 * arising from the use of this software.
10 *
11 * Permission is granted to anyone to use this software for any purpose,
12 * including commercial applications, and to alter it and redistribute it
13 * freely, subject to the following restrictions:
14 *
15 * 1. The origin of this software must not be misrepresented; you must not
16 *    claim that you wrote the original software. If you use this software
17 *    in a product, an acknowledgment in the product documentation would be
18 *    appreciated but is not required.
19 * 2. Altered source versions must be plainly marked as such, and must not be
20 *    misrepresented as being the original software.
21 * 3. This notice may not be removed or altered from any source distribution.
22 */
23
24/**
25 * @file
26 * Computes the Adler-32 checksum of a data stream
27 *
28 * This is a modified version based on adler32.c from the zlib library.
29 * @author Mark Adler
30 * @ingroup lavu_adler32
31 */
32
33#include "config.h"
34#include "adler32.h"
35#include "intreadwrite.h"
36#include "macros.h"
37
38#define BASE 65521L /* largest prime smaller than 65536 */
39
40#define DO1(buf)  { s1 += *buf++; s2 += s1; }
41#define DO4(buf)  DO1(buf); DO1(buf); DO1(buf); DO1(buf);
42#define DO16(buf) DO4(buf); DO4(buf); DO4(buf); DO4(buf);
43
44AVAdler av_adler32_update(AVAdler adler, const uint8_t *buf, size_t len)
45{
46    unsigned long s1 = adler & 0xffff;
47    unsigned long s2 = adler >> 16;
48
49    while (len > 0) {
50#if HAVE_FAST_64BIT && HAVE_FAST_UNALIGNED && !CONFIG_SMALL
51        unsigned len2 = FFMIN((len-1) & ~7, 23*8);
52        if (len2) {
53            uint64_t a1= 0;
54            uint64_t a2= 0;
55            uint64_t b1= 0;
56            uint64_t b2= 0;
57            len -= len2;
58            s2 += s1*len2;
59            while (len2 >= 8) {
60                uint64_t v = AV_RN64(buf);
61                a2 += a1;
62                b2 += b1;
63                a1 +=  v    &0x00FF00FF00FF00FF;
64                b1 += (v>>8)&0x00FF00FF00FF00FF;
65                len2 -= 8;
66                buf+=8;
67            }
68
69            //We combine the 8 interleaved adler32 checksums without overflows
70            //Decreasing the number of iterations would allow below code to be
71            //simplified but would likely be slower due to the fewer iterations
72            //of the inner loop
73            s1 += ((a1+b1)*0x1000100010001)>>48;
74            s2 += ((((a2&0xFFFF0000FFFF)+(b2&0xFFFF0000FFFF)+((a2>>16)&0xFFFF0000FFFF)+((b2>>16)&0xFFFF0000FFFF))*0x800000008)>>32)
75#if HAVE_BIGENDIAN
76                 + 2*((b1*0x1000200030004)>>48)
77                 +   ((a1*0x1000100010001)>>48)
78                 + 2*((a1*0x0000100020003)>>48);
79#else
80                 + 2*((a1*0x4000300020001)>>48)
81                 +   ((b1*0x1000100010001)>>48)
82                 + 2*((b1*0x3000200010000)>>48);
83#endif
84        }
85#else
86        while (len > 4  && s2 < (1U << 31)) {
87            DO4(buf);
88            len -= 4;
89        }
90#endif
91        DO1(buf); len--;
92        s1 %= BASE;
93        s2 %= BASE;
94    }
95    return (s2 << 16) | s1;
96}
97