bits/src/bits.c

/* bits - pipe the bits of each byte from stdin to stdout
 *
 * usage: bits [<mask>]
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define BUFFER_SIZE 4096
#define IGNORE(param) do { (void)(param); } while(0)

static inline int sfread(void* out, size_t *restrict size, FILE* f)
{
	return !!(*size = (size_t)fread(out, 1, *size, f));
}

static int fwrite_all(const void* _buf, size_t sz, size_t num, FILE* out)
{
	register size_t w, done=0;
	register const unsigned char* buf = _buf;
	while( (w = fwrite(buf+done, sz, num-done, out)) > 0 && done < num) done+=w;
	if (done!=num) return 0;
	else return 1;
}

static void pbits(char out[restrict 8], unsigned char byte, const char bit[static 2])
{
	for(register int i=8; i --> 0; byte >>= 1) *out++=((int)bit[byte & 1]);
}

static inline int check(int val, const char* msg)
{
	if(val) return val;
	fprintf(stderr, "error: %s\n", msg);
	exit(1);
}

int main(int argc, char **argv)
{
	IGNORE(argc);

	const char* mask = argv[1] && check(strlen(argv[1]) > 1, "expected 2 character mask") ? argv[1] : "01";
	unsigned char buf[BUFFER_SIZE];
	char tbuf[BUFFER_SIZE * 8];
	size_t bsz = BUFFER_SIZE;

	while(sfread(buf, &bsz, stdin))
	{
		register size_t size = bsz;
		while(size --> 0) pbits(tbuf+(8*size), buf[size], mask);
		if(!fwrite_all(tbuf, 8, bsz, stdout)) { perror("Failed to write"); return 1; }
	}

	return 0;
}