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✏️ Editing: 03_compress_custom.c

///////////////////////////////////////////////////////////////////////////////
//
/// \file       03_compress_custom.c
/// \brief      Compress in multi-call mode using x86 BCJ and LZMA2
///
/// Usage:      ./03_compress_custom < INFILE > OUTFILE
///
/// Example:    ./03_compress_custom < foo > foo.xz
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include <stdbool.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <lzma.h>

static bool
init_encoder(lzma_stream *strm)
{
	// Use the default preset (6) for LZMA2.
	//
	// The lzma_options_lzma structure and the lzma_lzma_preset() function
	// are declared in lzma/lzma12.h (src/liblzma/api/lzma/lzma12.h in the
	// source package or e.g. /usr/include/lzma/lzma12.h depending on
	// the install prefix).
	lzma_options_lzma opt_lzma2;
	if (lzma_lzma_preset(&opt_lzma2, LZMA_PRESET_DEFAULT)) {
		// It should never fail because the default preset
		// (and presets 0-9 optionally with LZMA_PRESET_EXTREME)
		// are supported by all stable liblzma versions.
		//
		// (The encoder initialization later in this function may
		// still fail due to unsupported preset *if* the features
		// required by the preset have been disabled at build time,
		// but no-one does such things except on embedded systems.)
		fprintf(stderr, "Unsupported preset, possibly a bug\n");
		return false;
	}

// Now we could customize the LZMA2 options if we wanted. For example,
	// we could set the the dictionary size (opt_lzma2.dict_size) to
	// something else than the default (8 MiB) of the default preset.
	// See lzma/lzma12.h for details of all LZMA2 options.
	//
	// The x86 BCJ filter will try to modify the x86 instruction stream so
	// that LZMA2 can compress it better. The x86 BCJ filter doesn't need
	// any options so it will be set to NULL below.
	//
	// Construct the filter chain. The uncompressed data goes first to
	// the first filter in the array, in this case the x86 BCJ filter.
	// The array is always terminated by setting .id = LZMA_VLI_UNKNOWN.
	//
	// See lzma/filter.h for more information about the lzma_filter
	// structure.
	lzma_filter filters[] = {
		{ .id = LZMA_FILTER_X86, .options = NULL },
		{ .id = LZMA_FILTER_LZMA2, .options = &opt_lzma2 },
		{ .id = LZMA_VLI_UNKNOWN, .options = NULL },
	};

// Initialize the encoder using the custom filter chain.
	lzma_ret ret = lzma_stream_encoder(strm, filters, LZMA_CHECK_CRC64);

if (ret == LZMA_OK)
		return true;

const char *msg;
	switch (ret) {
	case LZMA_MEM_ERROR:
		msg = "Memory allocation failed";
		break;

case LZMA_OPTIONS_ERROR:
		// We are no longer using a plain preset so this error
		// message has been edited accordingly compared to
		// 01_compress_easy.c.
		msg = "Specified filter chain is not supported";
		break;

case LZMA_UNSUPPORTED_CHECK:
		msg = "Specified integrity check is not supported";
		break;

default:
		msg = "Unknown error, possibly a bug";
		break;
	}

fprintf(stderr, "Error initializing the encoder: %s (error code %u)\n",
			msg, ret);
	return false;
}

// This function is identical to the one in 01_compress_easy.c.
static bool
compress(lzma_stream *strm, FILE *infile, FILE *outfile)
{
	lzma_action action = LZMA_RUN;

uint8_t inbuf[BUFSIZ];
	uint8_t outbuf[BUFSIZ];

strm->next_in = NULL;
	strm->avail_in = 0;
	strm->next_out = outbuf;
	strm->avail_out = sizeof(outbuf);

while (true) {
		if (strm->avail_in == 0 && !feof(infile)) {
			strm->next_in = inbuf;
			strm->avail_in = fread(inbuf, 1, sizeof(inbuf),
					infile);

if (ferror(infile)) {
				fprintf(stderr, "Read error: %s\n",
						strerror(errno));
				return false;
			}

if (feof(infile))
				action = LZMA_FINISH;
		}

lzma_ret ret = lzma_code(strm, action);

if (strm->avail_out == 0 || ret == LZMA_STREAM_END) {
			size_t write_size = sizeof(outbuf) - strm->avail_out;

if (fwrite(outbuf, 1, write_size, outfile)
					!= write_size) {
				fprintf(stderr, "Write error: %s\n",
						strerror(errno));
				return false;
			}

strm->next_out = outbuf;
			strm->avail_out = sizeof(outbuf);
		}

if (ret != LZMA_OK) {
			if (ret == LZMA_STREAM_END)
				return true;

const char *msg;
			switch (ret) {
			case LZMA_MEM_ERROR:
				msg = "Memory allocation failed";
				break;

case LZMA_DATA_ERROR:
				msg = "File size limits exceeded";
				break;

default:
				msg = "Unknown error, possibly a bug";
				break;
			}

fprintf(stderr, "Encoder error: %s (error code %u)\n",
					msg, ret);
			return false;
		}
	}
}

extern int
main(void)
{
	lzma_stream strm = LZMA_STREAM_INIT;

bool success = init_encoder(&strm);
	if (success)
		success = compress(&strm, stdin, stdout);

lzma_end(&strm);

if (fclose(stdout)) {
		fprintf(stderr, "Write error: %s\n", strerror(errno));
		success = false;
	}

return success ? EXIT_SUCCESS : EXIT_FAILURE;
}

MR SKB