#define _XOPEN_SOURCE 500
#define _GNU_SOURCE

#include <assert.h>
#include <fcntl.h>
#include <limits.h>
#include <linux/fs.h>
#include <math.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/param.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <stdint.h>

#define Pread(fd, buf, size, offset) do {				\
	int _read = 0, _r;						\
	while (_read < size) {						\
		_r = pread(fd, buf, (size) - _read, (offset) + _read);	\
		if (_r <= 0)						\
			goto err;					\
		_read += _r;						\
	}								\
} while (0)

/* Marsaglia polar method
 */
double normal()
{
	double x, y, s;
	static double n = 0 / (double) 0;

	if (n == n) {
		x = n;
		n = 0 / (double) 0;
		return x;
	}
	
	do {
		x = random() / (double) (RAND_MAX / 2) - 1;
		y = random() / (double) (RAND_MAX / 2) - 1;

		s = x * x + y * y;
	} while (s >= 1);

	s = sqrt(-2 * log(s) / s);
	n =	y * s;
	return  x * s;
}

uint32_t fletcher32(uint16_t *data, size_t len)
{
        uint32_t sum1 = 0xffff, sum2 = 0xffff;
 
        while (len) {
                unsigned tlen = len > 360 ? 360 : len;
                len -= tlen;
                do {
                        sum1 += *data++;
                        sum2 += sum1;
                } while (--tlen);
                sum1 = (sum1 & 0xffff) + (sum1 >> 16);
                sum2 = (sum2 & 0xffff) + (sum2 >> 16);
        }
        /* Second reduction step to reduce sums to 16 bits */
        sum1 = (sum1 & 0xffff) + (sum1 >> 16);
        sum2 = (sum2 & 0xffff) + (sum2 >> 16);
        return sum2 << 16 | sum1;
}

long getblocks(int fd)
{
	long ret;
	struct stat statbuf;
	if (fstat(fd, &statbuf)) {
		perror("stat error");
		exit(EXIT_FAILURE);
	}
	ret = statbuf.st_size / 512;
	if (S_ISBLK(statbuf.st_mode))
		if (ioctl(fd, BLKGETSIZE, &ret)) {
			perror("ioctl error");
			exit(EXIT_FAILURE);
		}
	return ret;
}

int main(int argc, char **argv)
{
	bool walk = false, randsize = false, verbose = false, csum = false;
	int fd1, fd2 = 0, direct = 0, nbytes = 4096, j;
	unsigned long size, i, offset = 0;
	void *buf1 = NULL, *buf2 = NULL;
	uint32_t *csums = NULL;

	if (argc < 3) {
		printf("Please enter a cache device and raw device\n");
		exit(EXIT_FAILURE);
	}

	for (i = 1; i < argc; i++) {
		if (strcmp(argv[i], "direct") == 0)
			direct = O_DIRECT;
		else if (strcmp(argv[i], "walk") == 0)
			walk = true;
		else if (strcmp(argv[i], "verbose") == 0)
			verbose = true;
		else if (strcmp(argv[i], "size") == 0)
			randsize = true;
		else if (strcmp(argv[i], "csum") == 0)
			csum= true;
		else
			break;
	}

	fd1 = open(argv[i], O_RDONLY|direct);
	size = getblocks(fd1);

	if (!csum) {
		fd2 = open(argv[2], O_RDONLY|direct);
		size = MIN(size, getblocks(fd2));
	} else
		csums = calloc((size / 8 + 1), sizeof(*csums));

	if (fd1 == -1 || fd2 == -1) {
		perror("Error opening device");
		exit(EXIT_FAILURE);
	}

	size = size / 8 - 16;
	printf("size %li\n", size);

	if (posix_memalign(&buf1, 4096, 4096 * 16) ||
	    posix_memalign(&buf2, 4096, 4096 * 16)) {
		printf("Could not allocate buffers\n");
		exit(EXIT_FAILURE);
	}
	setvbuf(stdout, NULL, _IONBF, 0);

	for (i = 0;; i++) {
		if (randsize)
			nbytes = 4096 * (int) (drand48() * 16 + 1);

		offset += walk ? normal() * 100 : random();
		offset %= size;
		assert(offset < size);

		if (verbose)
			printf("Loop %li offset %li sectors %i\n",
			       i, offset << 3, nbytes >> 9);
		else if (!(i % 100))
			printf("Loop %li\n", i);

		Pread(fd1, buf1, nbytes, offset << 12);

		if (!csum) {
			Pread(fd2, buf2, nbytes, offset << 12);

			for (j = 0; j < nbytes; j += 512)
				if (memcmp(buf1 + j,
					   buf2 + j,
					   512)) {
					printf("Bad read! loop %li offset %li sectors %i, sector %i\n",
					       i, offset << 3, nbytes >> 9, j >> 9);
					exit(EXIT_FAILURE);
				}
		} else
			for (j = 0; j < nbytes / 4096; j++) {
				int c = fletcher32(buf1 + j * 4096, 4096);
				if (!csums[offset + j])
					csums[offset + j] = c;
				else if (csums[offset + j] != c) {
					printf("Bad read! loop %li offset %li sectors %i, sector %i\n",
					       i, offset << 3, nbytes >> 9, j << 3);
					exit(EXIT_FAILURE);
				}
			}
	}
err:
	perror("Read error");
	exit(EXIT_FAILURE);
}