[SSE Acc] Pi - Monte Carlo method

Makefile

all: pi

pi: pi.c
	gcc-4.8 -Wall -std=c99 -O2 pi.c -o pi-4.8
	gcc-5 -std=c99 -O2 pi.c -o pi-5
	gcc-6 -std=c99 -O2 -march=native -msse -mavx pi.c -o pi-6
	gcc-4.8 -Wall -std=c99 -O2 -msse -msse2 -mavx pi-sse.c -o pi-sse
	clang-3.8 -O2 pi.c -o pi-clang
	 

pi-sse.c

#include <stdio.h>
#include <stdint.h>
#include <x86intrin.h>

int main() {
	const int r = 20000;
	const int rr = r * r;
	int c = 0; double a;

	__m128i sse_ret = _mm_set_epi32(0, 0, 0, 0);
	for (int x = 0; x < r; x++) {
		int tr = rr-x*x;
		__m128i sse_iy = _mm_set_epi32(0, 1, 2, 3);
		__m128i sse_ic = _mm_set_epi32(4, 4, 4, 4);
		__m128i sse_i16= _mm_set_epi32(16, 16, 16, 16);
		__m128i sse_sy = _mm_set_epi32(0, 1, 4, 9);
		__m128i sse_i1 = _mm_set_epi32(1, 1, 1, 1);
		__m128i sse_bb = _mm_set_epi32(tr, tr, tr, tr);
		for (int it = 0; it < r/4; it++) {
			__m128i res = _mm_and_si128(_mm_cmplt_epi32(sse_sy, sse_bb), sse_i1);
			sse_ret = _mm_add_epi32(sse_ret, res);
			sse_sy = _mm_add_epi32(sse_sy, _mm_slli_epi32(sse_iy, 3));
			sse_sy = _mm_add_epi32(sse_sy, sse_i16);
			sse_iy = _mm_add_epi32(sse_iy, sse_ic);
		}
		/*
		   for (int y = 0; y < r; y++) {
		   if (y*y < tr) 
		   c++;
		   }
		 */
	}
	{
		static int32_t tmp[4] __attribute__ ((aligned (16)));
		_mm_store_si128((__m128i*) &tmp[0], sse_ret);
		c = tmp[0] + tmp[1] + tmp[2] + tmp[3];
	}
	a = c * 4. / rr;
	printf("%.8f\n", a);
	return 0;
}

pi.c

#include <stdio.h>

int main() {
	const int r = 20000;
	const int rr = r * r;
	int c = 0; double a;
	for (int x = 0; x < r; x++) {
		int tr = rr-x*x;
		for (int y = 0; y < r; y++) {
			if (y*y < tr) 
				c++;
		}
	}
	a = c * 4. / rr;
	printf("%.8f\n", a);
	return 0;
}