PS2/PSX OSDSYS and PS2LOGO decompressor

osdsys_decomp.cpp

#include <stdio.h>
#include <stdint.h>
#include <elf.h>
#include <string.h>

uint8_t *findDataSegment(uint8_t *buf)
{
	Elf32_Ehdr *ehdr = (Elf32_Ehdr *) buf;
	
	Elf32_Shdr *shdr = (Elf32_Shdr *)&buf[ehdr->e_shoff];
	
	uint8_t *strtab = 0;
	
	for (int i = 0; i < ehdr->e_shnum; i++)
	{
		if (shdr[i].sh_type == SHT_STRTAB)
		{
			strtab = &buf[shdr[i].sh_offset];
			break;
		}
	}
	
	if (strtab)
	{
		for (int i = 0; i < ehdr->e_shnum; i++)
		{
			if (strcmp(".data", (char *) &strtab[shdr[i].sh_name]) == 0)
				return &buf[shdr[i].sh_offset];
		}
	}

	return nullptr;
}

void lzDecompress(uint8_t *dest, uint8_t *source, uint32_t dest_size)
{
	uint8_t *ptr = dest;
	
	uint32_t flag = 0, count = 0, mask = 0, shift = 0;
	while(ptr - dest < dest_size)
	{
		if (count == 0)
		{
			count = 30;
			flag = __builtin_bswap32(*(uint32_t *) source);
			source += 4;			
			mask = 0x3fff >> (flag & 3);
			shift = 14 - (flag & 3);
		}

		if (flag & 0x80000000)
		{
			uint16_t off_size = __builtin_bswap16(*(uint16_t *) source);
			source += 2;
			uint16_t offset = (off_size & mask) + 1;
			for (uint16_t i = (off_size >> shift) + 3; i > 0; i--)
				*(ptr++) = *(ptr - offset);
		}
		else
			*(ptr++) = *(source++);
		
		count--;
		flag <<= 1;
	}
}

int main(int argc, char ** argv)
{
	if (argc != 3)
	{
		printf("Usage: %s <OSDSYS> <output>\n", argv[0]);
		return -1;
	}
	
	FILE *f = fopen(argv[1], "rb");
	fseek(f, 0, SEEK_END);
	int len = ftell(f);
	fseek(f, 0, SEEK_SET);
	
	uint8_t *buf = new uint8_t[len];
	fread(buf, 1, len, f);
	fclose(f);

	uint8_t *data = findDataSegment(buf);
	if (!data)
	{
		printf(".data segment is not found!\n");
		return -1;
	}
	
	uint32_t uncompressed_len = *(uint32_t *) data;
	
	uint8_t *unpacked = new uint8_t[uncompressed_len];
	lzDecompress(unpacked, &data[4], uncompressed_len);
	delete [] buf;
	
	FILE *fo = fopen(argv[2], "wb");
	fwrite(unpacked, 1, uncompressed_len, fo);
	fclose(fo);

	delete [] unpacked;
	return 0;
}