Simple, uncompressed DEFLATE compressor

deflate_file.c

#include <stdint.h>

/* block size must be 65535 or less */
#define MAX_BLOCK_SIZE 65535

#define START 1
#define FINISH 2

#define writebyte(c) do {if (outleft) {*out++ = (c); outleft--;} else return 1;} while (0)

#define writeword_le(w) do {writebyte((w) & 255); writebyte(((w) >> 8) & 255);} while (0)
#define writeword_be(w) do {writebyte(((w) >> 8) & 255); writebyte((w) & 255);} while (0)
#define writedword_be(d) do {writeword_be(((d) >> 16) & 65535); writeword_be((d) & 65535);} while (0)

int simple_deflate(uint8_t *out, unsigned *outlen_p, uint8_t const *in, unsigned inlen, uint32_t *adler32, unsigned flags) {
	unsigned outleft = *outlen_p;
	unsigned adl1, adl2;
	unsigned i;

	if (adler32) {
		if (flags & START) *adler32 = 0x00000001;
		adl1 = *adler32 & 0xffff;
		adl2 = *adler32 >> 16;
		for (i = 0; i < inlen; i++) {
			adl1 += in[i]; adl2 += adl1;
			adl1 %= 65521; adl2 %= 65521;
		}
		*adler32 = adl1 | adl2 << 16;
	}

	if (flags & START) {
		/* a valid, ASCII-compatible DEFLATE header */
		writebyte('x');
		writebyte('^');
	}

	while (inlen > MAX_BLOCK_SIZE) {
		/* not last block; uncompressed */
		writebyte(0);
		/* block length */
		writeword_le(MAX_BLOCK_SIZE);
		writeword_le(~MAX_BLOCK_SIZE);
		for (i = 0; i < MAX_BLOCK_SIZE; i++) {
			writebyte(*in++);
			inlen--;
		}
	}

	if (inlen > 0 || (flags & FINISH)) {
		/* last block?; uncompressed */
		writebyte(!!(flags & FINISH));
		/* block length */
		writeword_le(inlen);
		writeword_le(~inlen);
		while (inlen) {
			writebyte(*in++);
			inlen--;
		}
	}

	if (adler32 && (flags & FINISH)) {
		/* Adler32 checksum footer */
		writedword_be(*adler32);
	}

	*outlen_p -= outleft;
	return 0;
}

#define READ_BLOCK_SIZE (MAX_BLOCK_SIZE * 2)

#include <stdio.h>

int main(int arg_c, char **arg_v) {
	uint8_t inbuf[READ_BLOCK_SIZE], outbuf[2 + READ_BLOCK_SIZE + 4 * (READ_BLOCK_SIZE / MAX_BLOCK_SIZE + 1) + 4];
	unsigned inlen, outlen;
	unsigned flags = START;
	uint32_t adler32;

	if (arg_c < 3) return 1;
	FILE *infile = fopen(arg_v[1], "rb"); if (!infile) return 2;
	FILE *outfile = fopen(arg_v[2], "wb"); if (!outfile) {fclose(infile); return 3;}

	while (!feof(infile)) {
		inlen = fread(inbuf, 1, READ_BLOCK_SIZE, infile);
		outlen = sizeof(outbuf);

		if (feof(infile))
			flags |= FINISH;

		if (simple_deflate(outbuf, &outlen, inbuf, inlen, &adler32, flags)) { fclose(infile); fclose(outfile); return -1; }

		flags &= ~START;

		fwrite(outbuf, 1, outlen, outfile);
	}

	fclose(infile);
	fclose(outfile);
	return 0;
}