1 /*
2 Copyright 2013 Google Inc. All Rights Reserved.
3
4 Licensed under the Apache License, Version 2.0 (the "License");
5 you may not use this file except in compliance with the License.
6 You may obtain a copy of the License at
7
8 http://www.apache.org/licenses/LICENSE-2.0
9
10 Unless required by applicable law or agreed to in writing, software
11 distributed under the License is distributed on an "AS IS" BASIS,
12 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 See the License for the specific language governing permissions and
14 limitations under the License.
15
16 Author: lode.vandevenne@gmail.com (Lode Vandevenne)
17 Author: jyrki.alakuijala@gmail.com (Jyrki Alakuijala)
18 */
19
20 #include "gzip_container.h"
21 #include "util.h"
22
23 #include <stdio.h>
24
25 #include "deflate.h"
26
27 /* Table of CRCs of all 8-bit messages. */
28 static unsigned long crc_table[256];
29
30 /* Flag: has the table been computed? Initially false. */
31 static int crc_table_computed = 0;
32
33 /* Makes the table for a fast CRC. */
MakeCRCTable()34 static void MakeCRCTable() {
35 unsigned long c;
36 int n, k;
37 for (n = 0; n < 256; n++) {
38 c = (unsigned long) n;
39 for (k = 0; k < 8; k++) {
40 if (c & 1) {
41 c = 0xedb88320L ^ (c >> 1);
42 } else {
43 c = c >> 1;
44 }
45 }
46 crc_table[n] = c;
47 }
48 crc_table_computed = 1;
49 }
50
51
52 /*
53 Updates a running crc with the bytes buf[0..len-1] and returns
54 the updated crc. The crc should be initialized to zero.
55 */
UpdateCRC(unsigned long crc,const unsigned char * buf,size_t len)56 static unsigned long UpdateCRC(unsigned long crc,
57 const unsigned char *buf, size_t len) {
58 unsigned long c = crc ^ 0xffffffffL;
59 unsigned n;
60
61 if (!crc_table_computed)
62 MakeCRCTable();
63 for (n = 0; n < len; n++) {
64 c = crc_table[(c ^ buf[n]) & 0xff] ^ (c >> 8);
65 }
66 return c ^ 0xffffffffL;
67 }
68
69 /* Returns the CRC of the bytes buf[0..len-1]. */
CRC(const unsigned char * buf,int len)70 static unsigned long CRC(const unsigned char* buf, int len) {
71 return UpdateCRC(0L, buf, len);
72 }
73
74 /*
75 Compresses the data according to the gzip specification.
76 */
ZopfliGzipCompress(const ZopfliOptions * options,const unsigned char * in,size_t insize,unsigned char ** out,size_t * outsize)77 void ZopfliGzipCompress(const ZopfliOptions* options,
78 const unsigned char* in, size_t insize,
79 unsigned char** out, size_t* outsize) {
80 unsigned long crcvalue = CRC(in, insize);
81 unsigned char bp = 0;
82
83 ZOPFLI_APPEND_DATA(31, out, outsize); /* ID1 */
84 ZOPFLI_APPEND_DATA(139, out, outsize); /* ID2 */
85 ZOPFLI_APPEND_DATA(8, out, outsize); /* CM */
86 ZOPFLI_APPEND_DATA(0, out, outsize); /* FLG */
87 /* MTIME */
88 ZOPFLI_APPEND_DATA(0, out, outsize);
89 ZOPFLI_APPEND_DATA(0, out, outsize);
90 ZOPFLI_APPEND_DATA(0, out, outsize);
91 ZOPFLI_APPEND_DATA(0, out, outsize);
92
93 ZOPFLI_APPEND_DATA(2, out, outsize); /* XFL, 2 indicates best compression. */
94 ZOPFLI_APPEND_DATA(3, out, outsize); /* OS follows Unix conventions. */
95
96 ZopfliDeflate(options, 2 /* Dynamic block */, 1,
97 in, insize, &bp, out, outsize);
98
99 /* CRC */
100 ZOPFLI_APPEND_DATA(crcvalue % 256, out, outsize);
101 ZOPFLI_APPEND_DATA((crcvalue >> 8) % 256, out, outsize);
102 ZOPFLI_APPEND_DATA((crcvalue >> 16) % 256, out, outsize);
103 ZOPFLI_APPEND_DATA((crcvalue >> 24) % 256, out, outsize);
104
105 /* ISIZE */
106 ZOPFLI_APPEND_DATA(insize % 256, out, outsize);
107 ZOPFLI_APPEND_DATA((insize >> 8) % 256, out, outsize);
108 ZOPFLI_APPEND_DATA((insize >> 16) % 256, out, outsize);
109 ZOPFLI_APPEND_DATA((insize >> 24) % 256, out, outsize);
110
111 if (options->verbose) {
112 fprintf(stderr,
113 "Original Size: %d, Gzip: %d, Compression: %f%% Removed\n",
114 (int)insize, (int)*outsize,
115 100.0 * (double)(insize - *outsize) / (double)insize);
116 }
117 }
118