bench-inline-vs-funptr-parse.c

/* benchmark for testing function call overhead of function pointer
 * integer lexem parsing, vs inlined integer lexem parsing
 */
 
#include <assert.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define BUFSIZE ((size_t)(1024*1024*1024))

struct timer {
        struct timespec ts;
};

void timer_reset(struct timer *timer)
{
        int r = clock_gettime(CLOCK_MONOTONIC_RAW, &timer->ts);
        assert(r == 0);
}

void timer_print(const char *fmt, struct timer *timer)
{
        struct timespec now;
        int r = clock_gettime(CLOCK_MONOTONIC_RAW, &now);
        assert(r == 0);
        time_t sec = now.tv_sec - timer->ts.tv_sec;
        long nsec = now.tv_nsec - timer->ts.tv_nsec;
        if (nsec < 0) {
                sec -= 1;
                nsec += 1000000000;
        }
        printf(fmt, (size_t) sec, (size_t) nsec / 1000000);
}

int intparser(char *c)
{
        int n = 0;
        while ('0' <= *c && *c <= '9')
                n = 10*n + *c++;
        return n;
}

void pointerparse(char *buf, size_t sz, int (parser)(char *))
{
        char *c = buf;
        char *end = buf + sz;
        int sum = 0;
        while (c + 8 < end) {
                c[7] = 0;
                sum += parser(c);
                c += 8;
        }
        printf("sum is %d\n", sum);
}

void inlineparse(char *buf, size_t sz)
{
        char *c = buf;
        char *end = buf + sz;
        int sum = 0;
        while (c + 8 <= end) {
                c[7] = 0;
                sum += intparser(c);
                c += 8;
        }
        printf("sum is %d\n", sum);
}

int main(int argc, const char *argv[])
{
        if (argc != 2 || (strcmp(argv[1], "function-pointer") != 0
                          && strcmp(argv[1], "inline") != 0)) {
                fprintf(stderr, "usage: %s <function-pointer|inline>\n",
                        argv[0]);
                exit(1);
        }

        int doinline = strcmp(argv[1], "function-pointer") != 0;

        printf("reading %zd bytes of input\n", BUFSIZE);

        char *buf = malloc(BUFSIZE);
        fread(buf, BUFSIZE, 1, stdin);

        printf("starting \"%s\" parse\n", argv[1]);

        struct timer timer;
        timer_reset(&timer);

        if (doinline)
                inlineparse(buf, BUFSIZE);
        else
                pointerparse(buf, BUFSIZE, intparser);

        timer_print("parsing time was %zd.%zd\n", &timer);

        return 0;
}