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

// memdance.c by Tyler Bletsch (Tyler.Bletsch@duke.edu) for ECE250
// Benchmark the rate of basically random memory access to a block of memory for a given amount of a time

double get_time() {
    struct timeval tv;
    gettimeofday(&tv, NULL);
    return (double)tv.tv_sec + tv.tv_usec/1000000.0;;
}

int main(int argc, char* argv[]) {
    size_t buffer_size=0; // bytes, given as an argument
    int execution_time; // seconds, given as argument
    int accesses_per_step = 1000000; // needs to be big enough that most of the time is spent hitting memory rather than computing time of day
    int idx_delta = 60029; // a fairly big prime so it won't wrap neatly for any common work size
    int steps = 0; // our counter
    if (argc != 3 || sscanf(argv[1],"%zd",&buffer_size)!=1 || sscanf(argv[2],"%d",&execution_time)!=1) {
        printf("Benchmark the rate of basically random memory access to a block of memory for a given amount of a time.\n\n");
        printf("Syntax: %s <size-in-bytes> <execution-time>\n",argv[0]);
        return 1;
    }
    
    double time_start = get_time();
    char* buf = (char*) malloc(buffer_size);
    int idx = 0;
    
    // outer loop: keep going until we're out of time
    while (get_time() < time_start+execution_time) {
        // inner loop: do a bunch of accesses as fast as possible
        // this inner loop is here so the overhead of determining the time doesn't significantly affect our measurement
        for (int s=0; s<accesses_per_step; s++) {
            buf[idx]++;
            idx = (idx+idx_delta) % buffer_size; // a really cheap form of "random", just advance by a fairly large prime number
        }
        steps++;
    }
    double elapsed = get_time() - time_start;
    double rate = (double)accesses_per_step*steps/elapsed;
    printf("Buffer %zd bytes. %d*%d accesses in %.1f seconds, %.3f MB/s.\n",buffer_size,steps,accesses_per_step,elapsed,rate/1024/1024);
    
    
}