/*
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Copyright 2013 Google Inc. All Rights Reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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Author: lode.vandevenne@gmail.com (Lode Vandevenne)
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Author: jyrki.alakuijala@gmail.com (Jyrki Alakuijala)
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*/
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#include "gzip_container.h"
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#include "util.h"
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#include <stdio.h>
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#include "deflate.h"
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/* Table of CRCs of all 8-bit messages. */
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static unsigned long crc_table[256];
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/* Flag: has the table been computed? Initially false. */
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static int crc_table_computed = 0;
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/* Makes the table for a fast CRC. */
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static void MakeCRCTable() {
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unsigned long c;
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int n, k;
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for (n = 0; n < 256; n++) {
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c = (unsigned long) n;
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for (k = 0; k < 8; k++) {
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if (c & 1) {
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c = 0xedb88320L ^ (c >> 1);
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} else {
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c = c >> 1;
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}
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}
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crc_table[n] = c;
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}
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crc_table_computed = 1;
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}
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/*
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Updates a running crc with the bytes buf[0..len-1] and returns
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the updated crc. The crc should be initialized to zero.
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*/
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static unsigned long UpdateCRC(unsigned long crc,
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const unsigned char *buf, size_t len) {
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unsigned long c = crc ^ 0xffffffffL;
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unsigned n;
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if (!crc_table_computed)
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MakeCRCTable();
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for (n = 0; n < len; n++) {
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c = crc_table[(c ^ buf[n]) & 0xff] ^ (c >> 8);
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}
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return c ^ 0xffffffffL;
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}
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/* Returns the CRC of the bytes buf[0..len-1]. */
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static unsigned long CRC(const unsigned char* buf, int len) {
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return UpdateCRC(0L, buf, len);
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}
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/*
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Compresses the data according to the gzip specification.
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*/
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void ZopfliGzipCompress(const ZopfliOptions* options,
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const unsigned char* in, size_t insize,
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unsigned char** out, size_t* outsize) {
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unsigned long crcvalue = CRC(in, insize);
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unsigned char bp = 0;
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ZOPFLI_APPEND_DATA(31, out, outsize); /* ID1 */
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ZOPFLI_APPEND_DATA(139, out, outsize); /* ID2 */
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ZOPFLI_APPEND_DATA(8, out, outsize); /* CM */
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ZOPFLI_APPEND_DATA(0, out, outsize); /* FLG */
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/* MTIME */
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ZOPFLI_APPEND_DATA(0, out, outsize);
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ZOPFLI_APPEND_DATA(0, out, outsize);
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ZOPFLI_APPEND_DATA(0, out, outsize);
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ZOPFLI_APPEND_DATA(0, out, outsize);
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ZOPFLI_APPEND_DATA(2, out, outsize); /* XFL, 2 indicates best compression. */
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ZOPFLI_APPEND_DATA(3, out, outsize); /* OS follows Unix conventions. */
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ZopfliDeflate(options, 2 /* Dynamic block */, 1,
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in, insize, &bp, out, outsize);
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/* CRC */
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ZOPFLI_APPEND_DATA(crcvalue % 256, out, outsize);
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ZOPFLI_APPEND_DATA((crcvalue >> 8) % 256, out, outsize);
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ZOPFLI_APPEND_DATA((crcvalue >> 16) % 256, out, outsize);
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ZOPFLI_APPEND_DATA((crcvalue >> 24) % 256, out, outsize);
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/* ISIZE */
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ZOPFLI_APPEND_DATA(insize % 256, out, outsize);
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ZOPFLI_APPEND_DATA((insize >> 8) % 256, out, outsize);
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ZOPFLI_APPEND_DATA((insize >> 16) % 256, out, outsize);
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ZOPFLI_APPEND_DATA((insize >> 24) % 256, out, outsize);
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if (options->verbose) {
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fprintf(stderr,
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"Original Size: %d, Gzip: %d, Compression: %f%% Removed\n",
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(int)insize, (int)*outsize,
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100.0 * (double)(insize - *outsize) / (double)insize);
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}
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}
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