mirror of https://github.com/haya3218/SDfmL.git
115 lines
2.5 KiB
C
115 lines
2.5 KiB
C
/*
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* zx7 decompress by Jari Komppa, under public domain / unlicense
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*
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* Heavily based on zx7 decompressor by Einar Saukas.
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* Einar Saukas requests that you mention the use of dx7, but
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* this is not enforced by any way.
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*
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* Note that compressor has a different license!
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*/
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#ifndef ZX7DECOMPRESS_H
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#define ZX7DECOMPRESS_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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struct zx7_io
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{
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unsigned char* input_data;
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unsigned char* output_data;
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size_t input_index;
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size_t output_index;
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int bit_mask;
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int bit_value;
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};
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static int zx7_read_byte(struct zx7_io *io) {
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return io->input_data[io->input_index++];
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}
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static int zx7_read_bit(struct zx7_io *io) {
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io->bit_mask >>= 1;
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if (io->bit_mask == 0) {
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io->bit_mask = 128;
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io->bit_value = zx7_read_byte(io);
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}
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return io->bit_value & io->bit_mask ? 1 : 0;
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}
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static int zx7_read_elias_gamma(struct zx7_io *io) {
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int i = 0;
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int value = 0;
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while (!zx7_read_bit(io)) {
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i++;
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}
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if (i > 15) {
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return -1;
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}
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value = 1;
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while (i--) {
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value = value << 1 | zx7_read_bit(io);
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}
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return value;
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}
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static int zx7_read_offset(struct zx7_io *io) {
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int value = 0;
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int i = 0;
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value = zx7_read_byte(io);
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if (value < 128) {
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return value;
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} else {
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i = zx7_read_bit(io);
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i = i << 1 | zx7_read_bit(io);
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i = i << 1 | zx7_read_bit(io);
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i = i << 1 | zx7_read_bit(io);
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return (value & 127 | i << 7) + 128;
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}
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}
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static void zx7_write_byte(struct zx7_io *io, int value) {
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io->output_data[io->output_index++] = value;
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}
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static void zx7_write_bytes(struct zx7_io *io, int offset, int length) {
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int i;
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while (length-- > 0) {
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i = io->output_index - offset;
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zx7_write_byte(io, io->output_data[i]);
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}
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}
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static int zx7_decompress(unsigned char *input_data, unsigned char *output_data) {
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struct zx7_io io;
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int length;
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io.input_data = input_data;
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io.output_data = output_data;
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io.input_index = 0;
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io.output_index = 0;
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io.bit_mask = 0;
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io.bit_value = 0;
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zx7_write_byte(&io, zx7_read_byte(&io));
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while (1) {
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if (!zx7_read_bit(&io)) {
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zx7_write_byte(&io, zx7_read_byte(&io));
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} else {
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length = zx7_read_elias_gamma(&io) + 1;
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if (length == 0) {
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return io.input_index;
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}
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zx7_write_bytes(&io, zx7_read_offset(&io) + 1, length);
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}
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}
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}
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#ifdef __cplusplus
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}
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#endif
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#endif // ZX7DECOMPRESS_H
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