103 lines
2.5 KiB
C
103 lines
2.5 KiB
C
#include <stdio.h>
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#include <stdint.h>
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#include <stdbool.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <assert.h>
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void opts(uint8_t byte, uint8_t *options)
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{
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*(options++) = byte | ((byte << 1) & 0xff);
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*(options++) = byte & (byte << 1);
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*(options++) = byte | ((byte >> 1) & 0xff);
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*(options++) = byte & (byte >> 1);
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}
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void write_all(int fd, const void *buf, size_t count) {
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while (count) {
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ssize_t written = write(fd, buf, count);
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if (written < 0) {
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fprintf(stderr, "write");
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exit(1);
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}
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count -= written;
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buf += written;
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}
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}
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int main()
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{
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static uint8_t source[0x4000];
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size_t size = read(STDIN_FILENO, &source, sizeof(source));
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unsigned pos = 0;
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assert(size <= 0x4000);
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while (size && source[size - 1] == 0) {
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size--;
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}
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uint8_t literals[8];
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size_t literals_size = 0;
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unsigned bits = 0;
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unsigned control = 0;
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unsigned prev[2] = {-1, -1}; // Unsigned to allow "not set" values
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while (true) {
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uint8_t byte = 0;
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if (pos == size){
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if (bits == 0) break;
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}
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else {
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byte = source[pos++];
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}
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if (byte == prev[0] || byte == prev[1]) {
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bits += 2;
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control <<= 1;
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control |= 1;
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control <<= 1;
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if (byte == prev[1]) {
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control |= 1;
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}
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}
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else {
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bits += 2;
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control <<= 2;
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uint8_t options[4];
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opts(prev[1], options);
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bool found = false;
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for (unsigned i = 0; i < 4; i++) {
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if (options[i] == byte) {
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// 01 = modify
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control |= 1;
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bits += 2;
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control <<= 2;
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control |= i;
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found = true;
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break;
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}
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}
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if (!found) {
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literals[literals_size++] = byte;
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}
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}
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prev[0] = prev[1];
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prev[1] = byte;
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if (bits >= 8) {
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uint8_t outctl = control >> (bits - 8);
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assert(outctl != 1);
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write_all(STDOUT_FILENO, &outctl, 1);
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write_all(STDOUT_FILENO, literals, literals_size);
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bits -= 8;
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control &= (1 << bits) - 1;
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literals_size = 0;
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}
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}
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uint8_t end_byte = 1;
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write_all(STDOUT_FILENO, &end_byte, 1);
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return 0;
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}
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