study.c

#include <sys/types.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <stdlib.h>
#include <signal.h>
#include <poll.h>
#include <string.h>
#include <stdio.h>
#include <math.h>
double packets;
double ttotal;
double t[16][256];
double tsq[16][256];
long long tnum[16][256];
double u[16][256];
double udev[16][256];
char n[16];

void tally(double timing)
{
    int j;
    int b;
    for (j = 0;j < 16;++j) {
        b = 255 & (int) n[j];
        ++packets;
        ttotal += timing;
        t[j][b] += timing;
        tsq[j][b] += timing * timing;
        tnum[j][b] += 1;
    }
}

int s;
int size;
void studyinput(FILE *fp)
{
    int j;
    char packet[2048];
    char response[40];
    struct pollfd p;
    for (;;) {
        if (size < 16) continue;
        if (size > sizeof packet) continue;
        /* a mediocre PRNG is sufficient here */
        for (j = 0;j < size;++j) packet[j] = random();
        for (j = 0;j < 16;++j) n[j] = packet[j];
        send(s,packet,size,0);
        p.fd = s;
        p.events = POLLIN;
        if (poll(&p,1,100) <= 0) continue;
        while (p.revents & POLLIN) {
            if (recv(s,response,sizeof response,0) == sizeof response) {
                if (!memcmp(packet,response,16)) {
                    unsigned int timing;
                    timing = *(unsigned int *) (response + 36);
                    timing -= *(unsigned int *) (response + 32);
                    /*if (timing < 1400) { [> clip tail to reduce noise <]*/
                        fprintf(fp, "%u\n", timing);
                        /*fflush(fp);*/
                        tally(timing);
                        return;
                    /*}*/
                }
            }
            if (poll(&p,1,0) <= 0) break;
        }
    }
}

void printpatterns(void)
{
    int j;
    int b;
    double taverage;
    taverage = ttotal / packets;
    for (j = 0;j < 16;++j)
    for (b = 0;b < 256;++b) {
        u[j][b] = t[j][b] / tnum[j][b];
        udev[j][b] = tsq[j][b] / tnum[j][b];
        udev[j][b] -= u[j][b] * u[j][b];
        udev[j][b] = sqrt(udev[j][b]);
    }

    for (j = 0;j < 16;++j) {
        for (b = 0;b < 256;++b) {
        printf("%2d %4d %3d %lld %.3f %.3f %.3f %.3f\n"
        ,j
        ,size
        ,b
        ,tnum[j][b]
        ,u[j][b]
        ,udev[j][b]
        ,u[j][b] - taverage
        ,udev[j][b] / sqrt(tnum[j][b])
        );
        }
    }
    fflush(stdout);
}

int timetoprint(long long inputs)
{
    if (inputs < 10000) return 0;
    if (!(inputs & (inputs - 1))) return 1;
    return 0;
}

int main(int argc,char **argv)
{
    struct sockaddr_in server;
    long long inputs = 0;
    if (!argv[1]) return 100;
    if (!inet_aton(argv[1],&server.sin_addr)) return 100;
    server.sin_family = AF_INET;
    server.sin_port = htons(10000);
    if (!argv[2]) return 100;
    size = atoi(argv[2]);
    while ((s = socket(AF_INET,SOCK_DGRAM,0)) == -1) sleep(1);
    while (connect(s,(struct sockaddr *) &server,sizeof server
    ) == -1) sleep(1);

    FILE *fp = fopen("/data/local/tmp/bern-timings.txt", "w+");
    for (;;) {
        studyinput(fp);
        ++inputs;
        if (timetoprint(inputs)) printpatterns();
    }
}