Makefile

CC = g++
LD = $(CC)

CC_FLAGS = -O2 -g0 -Wall
LD_FLAGS =

SRC = $(wildcard *.cpp)
OBJ = $(SRC:.cpp=.o)
BIN = $(SRC:.cpp=)

all: plot

build: $(BIN)

$(OBJ): %.o: %.cpp
	$(CC) $(CC_FLAGS) -o $@ -c $<

$(BIN): %: %.o
	$(LD) $(LD_FLAGS) -o $@ $<

run: time.dat time2.dat

time.dat: sum run.sh
	./run.sh

time2.dat: sum run2.sh
	./run2.sh

plot: time.png time2.png

time.png: time.gplot time.dat time2.dat
	gnuplot time.gplot

time2.png: time2.gplot time.dat time2.dat
	gnuplot time2.gplot

clean-images:
	rm -f time.png time2.png

clean: clean-images
	rm -f $(BIN) $(OBJ) *.dat

.PHONY: all build run plot clean-images clean

run.sh

#!/bin/bash

: > time.dat

for i in `seq 0 20`; do
    length=$((2**i))
    ./sum $length | head -1 >> time.dat
done

run2.sh

#!/bin/bash

: > time2.dat

for i in `seq 1 1024`; do
    ./sum $i | head -1 >> time2.dat
done

sum.cpp

/**
 * @file sum.cpp
 * @author Ian Yang
 * @date Created <2010-06-05 08:18:04>
 */
#include <iostream>
#include <ctime>
#include <cstdlib>

class Timer
{
    std::clock_t start_;
public:
    Timer()
    : start_(std::clock())
    {}

    double elapsed() const
    {
        return double(std::clock() - start_) / CLOCKS_PER_SEC;
    }
};

const std::size_t kTotalCount = 1 << 24;

void runTest(std::size_t slideLength);

int main(int argc, char *argv[])
{
    if (argc != 2)
    {
        std::cerr << "Usage: sum slideLength" << std::endl;
        return 1;
    }

    std::size_t slideLength = 0;
    slideLength = std::atol(argv[1]);
    if (slideLength == 0 || slideLength > kTotalCount)
    {
        std::cerr << "Invalid slideLength: " << argv[1] << std::endl;
        return 2;
    }

    runTest(slideLength);

    return 0;
}

void runTest(std::size_t slideLength)
{
    double* elements = new double[kTotalCount];
    for (std::size_t i = 0; i < kTotalCount; ++i)
    {
        elements[i] = i;
    }

    Timer timer;
    double sum = 0.0;

    std::size_t slideStep = kTotalCount / slideLength;

    static const std::size_t kRepeat = 1;
    for (std::size_t loopId = 0; loopId < kRepeat; ++loopId)
    {
        for (std::size_t outerLoopId = 0;
             outerLoopId < slideStep; ++outerLoopId)
        {
            for (std::size_t index = outerLoopId;
                 index < kTotalCount; index += slideStep)
            {
                sum += elements[index];
            }
        }
    }

    std::cout.setf(std::ios::fixed);
    std::cout.precision(8);
    std::cout << slideLength << " " << timer.elapsed() << std::endl;
    std::cout << sum << std::endl; // use the sum to avoid optimization
}

time.gplot

set terminal png font "DroidSansMono"
set output "time.png"

set logscale x 2
set xtics 2 rotate
set grid x y
set style data linespoints

set xlabel "slide length"
set ylabel "time (s)"

plot "time.dat", "time2.dat"

time2.gplot

set terminal png font "DroidSansMono" size 4000,600
set output "time2.png"

set logscale x 2
set xtics 2 rotate
set grid x y
set style data linespoints

set xlabel "slide length"
set ylabel "time (s)"

plot [x=1:1024] "time.dat", "time2.dat"