hex

unhex.c (1124B)

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

const char *skip = " \t\r\n";

char
hex2nib(char c, ssize_t *pos)
{
	switch (c) {
	case '0' ... '9':
		*pos += 1;
		return c - '0';
	case 'a' ... 'f':
		*pos += 1;
		return c - 'a' + 10;
	case 'A' ... 'F':
		*pos += 1;
		return c - 'A' + 10;
	}

	if (!strchr(skip, c)) {
		fprintf(stderr, "Invalid hex '%c' at position %lu\n", c, *pos);
		exit(1);
	}

	return 0;
}

void
fromhex(int fd)
{
	ssize_t pos, i, nread;
	char buf[4096], nib;

	pos = 0;
	while (1) {
		nread = read(fd, buf, sizeof(buf));
		if (nread <= 0) break;

		for (i = 0; i < nread; i++) {
			if (pos % 2 == 0) {
				nib = hex2nib(buf[i], &pos);
			} else {
				putchar((nib << 4) | hex2nib(buf[i], &pos));
			}
		}
	}

	if (pos % 2 != 0)
		putchar(nib << 4);
}

int
main(int argc, const char **argv)
{
	int i, fd;

	if (argc > 1) {
		for (i = 1; i < argc; i++) {
			fd = open(argv[i], O_RDONLY);
			if (fd < 0) {
				fprintf(stderr, "Could not open file: %s\n",
					argv[i]);
				continue;
			}
			fromhex(fd);
			close(fd);
		}
	} else {
		fromhex(0);
	}
}