/*
 * inline-asm-array-sum - an example of inline assembly accessing arrays
 *
 * Copyright (C) 2013  Antonio Ospite <ospite@studenti.unina.it>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

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

#define SIZE 10000001

static int array_sum(int *values, unsigned int n)
{
	int sum = 0;

#if defined(__x86_64__)
	__asm__(
		"movq $0, %%rdi\n\t" /* i = 0 */
		".REPEAT:\n\t"
		"cmpl %%edi, %%ecx\n\t" /* if (i == n) */
		"je .DONE\n\t"
		"movq (%%rbx,%%rdi,4), %%rdx\n\t" /* tmp = values[i]; 64 bit register */
		"addl %%edx, %%eax\n\t" /* sum += tmp[31:0]; */
		"incl %%edi\n\t" /* i++ */
		"jmp .REPEAT\n\t"
		".DONE:\n\t"
		: "=a"(sum)
		: "b"(values), "c"(n), "0"(sum)
		: "%rdx", "%rdi", "cc"
		);
#else
	unsigned int i;
	for (i = 0; i < n; i++)
		sum += values[i];
#endif
	return sum;
}

int main(void)
{
	int *values;
	int i;
	int sum;
	int expected;
	int n = SIZE;

	srand(time(0));

	values = malloc(n * sizeof(*values));

	expected = 0;
	for (i = 0; i < n; i++) {
		values[i] = rand();
		expected += values[i];
	}

	sum = array_sum(values, n);

	printf("expected = %d; sum = %d; %s\n", expected, sum, sum == expected ? "OK" : "FAILED");
	return (sum == expected);
}