# 2016q3 Homework1(Compute Pi)
contributed by <`Weinux`>
###### tags:`Computepi` `Weinux`

## 預期目標

* 學習透過離散微積分求圓周率
* Leibniz formula for π
* 積分計算圓周率π
* Function
* 著手透過 SIMD 指令作效能最佳化

## 開發環境
* OS：Lubuntu 15.10
* Linux系統版本: 4.2.0-42-generic
* CPU: Intel(R) Core(TM) i5-2410M CPU @ 2.30GHz
* MEM: 6GB
* Cache:
* L1d cache: 32K
* L1i cache: 32K
* L2 cache: 256K
* L3 cache: 3072K

---

double computePi_v1(size_t N)
{
    double pi = 0.0;
    double dt = 1.0 / N;                // dt = (b-a)/N, b = 1, a = 0
    for (size_t i = 0; i < N; i++) {
        double x = (double) i / N;      // x = ti = a+(b-a)*i/N = i/N
        pi += dt / (1.0 + x * x);       // integrate 1/(1+x^2), i = 0....N
    }
    return pi * 4.0;
}

---

CC = gcc
CFLAGS = -O0 -std=gnu99 -Wall -fopenmp -mavx
EXECUTABLE = \
	time_test_baseline time_test_openmp_2 time_test_openmp_4 \
	time_test_avx time_test_avxunroll \
	benchmark_clock_gettime

default: computepi.o
	$(CC) $(CFLAGS) computepi.o time_test.c -DBASELINE -o time_test_baseline
	$(CC) $(CFLAGS) computepi.o time_test.c -DOPENMP_2 -o time_test_openmp_2
	$(CC) $(CFLAGS) computepi.o time_test.c -DOPENMP_4 -o time_test_openmp_4
	$(CC) $(CFLAGS) computepi.o time_test.c -DAVX -o time_test_avx
	$(CC) $(CFLAGS) computepi.o time_test.c -DAVXUNROLL -o time_test_avxunroll
	$(CC) $(CFLAGS) computepi.o benchmark_clock_gettime.c -o benchmark_clock_gettime

.PHONY: clean default

%.o: %.c
	$(CC) -c $(CFLAGS) $< -o $@ 

check: default
	time ./time_test_baseline
	time ./time_test_openmp_2
	time ./time_test_openmp_4
	time ./time_test_avx
	time ./time_test_avxunroll

gencsv: default
	for i in `seq 100 5000 25000`; do \
		printf "%d," $$i;\
		./benchmark_clock_gettime $$i; \
	done > result_clock_gettime.csv	

clean:
	rm -f $(EXECUTABLE) *.o *.s result_clock_gettime.csv