another mystery

funproblem.c

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

#include "roaring.c"
int main() {
    size_t bitmapcount = 2;
    size_t size = 1000000;
    struct timeval st, et;
    int elapsed;
    roaring_bitmap_t **bitmaps =
        (roaring_bitmap_t **)malloc(sizeof(roaring_bitmap_t *) * bitmapcount);
    for (size_t i = 0; i < bitmapcount; i++) {
        bitmaps[i] = roaring_bitmap_from_range(0, 1000000, 1);
        for (size_t j = 0; j < size / 20; j++)
            roaring_bitmap_remove(bitmaps[i], rand() % size);
        // optionally run
        roaring_bitmap_printf_describe(bitmaps[i]);
    }
    gettimeofday(&st, NULL);

    roaring_bitmap_t *answer1 = roaring_bitmap_or_many(bitmapcount, bitmaps);
    gettimeofday(&et, NULL);
    elapsed = ((et.tv_sec - st.tv_sec) * 1000000) + (et.tv_usec - st.tv_usec);
    printf("roaring_bitmap_or_many time: %d micro seconds\n", elapsed);
    gettimeofday(&st, NULL);

    roaring_bitmap_t *answer2 = roaring_bitmap_copy(bitmaps[0]);
    for (size_t i = 1; i < bitmapcount; i++) {
        roaring_bitmap_or_inplace(answer2, bitmaps[i]);
    }
    gettimeofday(&et, NULL);

    elapsed = ((et.tv_sec - st.tv_sec) * 1000000) + (et.tv_usec - st.tv_usec);
    printf("naive time: %d micro seconds\n", elapsed);
    for (size_t i = 0; i < bitmapcount; i++) {
        roaring_bitmap_run_optimize(bitmaps[i]);
                roaring_bitmap_printf_describe(bitmaps[i]);

    }
    gettimeofday(&st, NULL);

    roaring_bitmap_t *answer3 = roaring_bitmap_or_many(bitmapcount, bitmaps);
    gettimeofday(&et, NULL);
    elapsed = ((et.tv_sec - st.tv_sec) * 1000000) + (et.tv_usec - st.tv_usec);
    printf("roaring_bitmap_or_many time: %d micro seconds\n", elapsed);
    gettimeofday(&st, NULL);

    roaring_bitmap_t *answer4 = roaring_bitmap_copy(bitmaps[0]);
    for (size_t i = 1; i < bitmapcount; i++) {
        roaring_bitmap_or_inplace(answer2, bitmaps[i]);
    }
    gettimeofday(&et, NULL);

    elapsed = ((et.tv_sec - st.tv_sec) * 1000000) + (et.tv_usec - st.tv_usec);
    printf("naive OR time: %d micro seconds\n", elapsed);
    for (size_t i = 0; i < bitmapcount; i++) {
        roaring_bitmap_free(bitmaps[i]);
    }
    free(bitmaps);
    roaring_bitmap_free(answer1);
    return 0;
}