#if 0 /* Magic self-executing C source code.  Run "sh cmpoffsets.c"   -dnelson
set -ex
gcc -g -Wall -O2 -march=i686 $0 -o cmpoffsets
exit 0
*/
#endif


#include <stdio.h>
#include <netinet/in.h>
#include <stdlib.h>

unsigned int boundarycheck(unsigned int number);

int main(int argc, char **argv)
{
	unsigned int i;
	FILE *in;
	int tosmall = 0;
	unsigned int firstbad = -1, lastbad = -1;
	unsigned int firstbadoff = 0, lastbadoff = 0;
	int failed = 0;

	if (argc != 2)
	{
		printf("Usage: cmpoffsets file.copy\n");
		exit(1);
	}
	in = fopen(argv[1], "rb");
	if (!in)
	{
		perror("cannot open file");
		exit(1);
	}
	setvbuf(in, malloc(65536), _IOFBF, 65536);

	for (i = 0; i < 1536 * 1024 * 1024 && !tosmall; i += 4)
	{
		unsigned int o;

		if (fread(&o, 4, 1, in) != 1)
		{
			o = htonl(i);
			tosmall = 1;
		}
		o = ntohl(o);
		if (o != i)
		{
			failed = 1;
			if (lastbad != i - 4)
			{
				firstbad = i;
				firstbadoff = o;
			}
			lastbad = i;
			lastbadoff = o;
		} else
		{
			if (lastbad == i - 4)
			{
				if (firstbad == lastbad)
				{	/* range of one */
					printf("%u (4) (held data from %u)\n", firstbad, firstbadoff);
				} else
				{	/* range > 1 */
					printf("%u-%u (%u) (held data from %u-%u)\n", firstbad, lastbad + 3,
					       lastbad + 4 - firstbad,
					       firstbadoff, lastbadoff + 3);
					if (boundarycheck(firstbadoff) > 2048)
						printf(" starts at a %u-byte block\n", boundarycheck(firstbadoff));
					if (boundarycheck(lastbadoff + 4) > 2048)
						printf(" ends at a %u-byte block\n", boundarycheck(lastbadoff + 4));
				}

				firstbad = lastbad = -1;
			}
		}
	}
	if (tosmall)
	{
		printf("file is truncated\n");
		failed = 1;
	}
	return failed;
}

unsigned int boundarycheck(unsigned int number)
{
	long long block = 1;
	while (block < number)
	{
		block *= 2;
		if (number / block * block != number)
			break;
	}
	return block;
}