areas.c

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define WIDTH (99 * 40)
#define HEIGHT (99 * 25)

static double timespec2d(struct timespec *ts)
{
    return ts->tv_sec + ts->tv_nsec / 1000000000.;
}

int main(int argc, char **argv)
{
    static uint8_t areas[HEIGHT][WIDTH] = {};
    int modified = 0;

    for (size_t y = 0; y < HEIGHT; ++y)
        for (size_t x = 0; x < WIDTH; ++x)
            areas[y][x] = (rand() >> 8) & 255; // このマスクを3にすると分岐予測があたらなくなる

    struct timespec start, end;
    timespec_get(&start, TIME_UTC);

    for (size_t y = 0; y < HEIGHT; ++y) {
        for (size_t x = 0; x < WIDTH; ++x) {
            uint8_t id = areas[y][x];
            if ((x > 0 && id == areas[y][x - 1]) ||
                (y > 0 && id == areas[y - 1][x])) {
                areas[y][x] = 0;
                modified = 1;
            }
        }
    }

    timespec_get(&end, TIME_UTC);

    printf("modified: %d\n", modified);
    printf("elapsed: %f\n", timespec2d(&end) - timespec2d(&start));

    return 0;
}