SameBoy/BootROMs/pb12.c

91 lines
2.2 KiB
C

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