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


#define DEFAULT_PADSIZE 0x4000
#define PADCHAR 0

unsigned long padsize = DEFAULT_PADSIZE;
int verbose;


void usage(char *prog, int rc)
{
	char *p;

	if((p = strrchr(prog, '/'))) prog = p + 1;

	printf("usage: %s [-p<size> -hv] [infile [outfile]]\n\n"
		   "where: -p <size>  is the padsize (default %d)\n"
		   "       -h         gives this help\n"
		   "       -v         ups the verbosity\n"
		   , prog, DEFAULT_PADSIZE);

	exit(rc);
}


int main(int argc, char *argv[])
{
	int c;
	int in, out;
	unsigned long size = 0, pad;
	int n, w;
	char buf[4096];


	while((c = getopt(argc, argv, "hp:v")) != EOF)
		switch(c) {
		case 'h': usage(argv[0], 0);
		case 'p': padsize = strtol(optarg, 0, 0); break;
		case 'v': ++verbose; break;
		default: usage(argv[0], 2);
		}

	if(optind < argc) {
		char *fname = argv[optind++];

		if((in = open(fname, O_RDONLY)) < 0) {
			perror(fname);
			exit(1);
		}
	} else
		in = 0;


	if(optind < argc) {
		char *fname = argv[optind++];

		if((out = open(fname, O_WRONLY | O_TRUNC | O_CREAT, 0644)) < 0) {
			perror(fname);
			exit(1);
		}
	} else
		out = 1;

	while((n = read(in, buf, sizeof(buf))) > 0) {
		if((w = write(out, buf, n)) != n) {
			printf("ERROR: short write %d of %d\n", w, n);
			exit(1);
		}
		size += n;
	}

	close(in);

	if(size % padsize) {
		pad = padsize - size % padsize;

		if(verbose) printf("File size 0x%lx pad 0x%lx to 0x%lx\n", size, pad, size + pad);

		memset(buf, PADCHAR, sizeof(buf));

		while(pad > 0) {
			n = pad > sizeof(buf) ? sizeof(buf) : pad;
			if((w = write(out, buf, n)) != n) {
				printf("ERROR: short write %d of %d\n", w, n);
				exit(1);
			}
			pad -= n;
		}
	} else if(verbose)
		printf("Already aligned\n");

	close(out);

	return 0;
}

/*
 * Local Variables:
 * compile-command: "gcc -O3 -Wall padit.c -o padit"
 * End:
 */