Timing for shift vs mask

makefile

all: thing run

thing:
	gcc -Wall -Wextra -std=c99 -O3 test.c -o test

run:
	./test

plot_times.ipynb

test.c

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

// void qsort(void* base, size_t num, size_t size, int (*comparator)(const void*,const void*));

    // printf("\nSorted:\n");
    // for(int i = 0; i < N; i++){
    //     printf("%" PRIu64 "\n", a[i]);
    // }

    // printf("Unsorted:\n");
    // for(int i = 0; i < N; i++){
    //     printf("%" PRIu64 "\n", a[i]);
    // }

        // printf("%" PRIu64 "\n", t >> 60);


#define IMAX_BITS(m) ((m)/((m)%255+1) / 255%255*8 + 7-86/((m)%255+12))
#define RAND_MAX_WIDTH IMAX_BITS(RAND_MAX)
_Static_assert((RAND_MAX & (RAND_MAX + 1u)) == 0, "RAND_MAX not a Mersenne number");


uint64_t rand64(void) {
  uint64_t r = 0;
  for (int i = 0; i < 64; i += RAND_MAX_WIDTH) {
    r <<= RAND_MAX_WIDTH;
    r ^= (unsigned) rand();
  }
  return r;
}


#define MAKE_CMP_FUNC(name, expression) \
    int (name)(const void *p, const void *q){ \
        uint64_t l = *(const uint64_t *)p; \
        uint64_t r = *(const uint64_t *)q; \
        expression \
        if (l < r) return -1; \
        if (l > r) return +1; \
        return 0; \
    } \



MAKE_CMP_FUNC(cmp_std,
)

MAKE_CMP_FUNC(cmp_shift,
    l <<= 12;
    r <<= 12;
)

MAKE_CMP_FUNC(cmp_mask,
    uint64_t m = 0x000fffffffffffff;
    l &= m;
    r &= m;
)


// todo: maybe make this a function
#define DO_TIMING(cmp_func) \
    copy(a, b, N);  \
    start_time = clock();  \
    qsort((void*)b, N, sizeof(b[0]), (cmp_func));  \
    end_time = clock();  \
    time_elapsed = (end_time - start_time)/CLOCKS_PER_SEC;  \
    printf(#cmp_func ": %f\n", time_elapsed);  \


void copy(uint64_t * x, uint64_t * y, uint64_t N){
    for(uint64_t i = 0; i < N; i++){
        y[i] = x[i];
    }
}

int main() {
    uint64_t N = 3000000;
    uint64_t a[N];
    uint64_t b[N];
    double start_time, end_time, time_elapsed;
    srand(3);

    for(uint64_t i = 0; i < N; i++){
        a[i] = rand64();
    }

    for(uint64_t i = 0; i < 10; i++){
        DO_TIMING(cmp_std);
        DO_TIMING(cmp_shift);
        DO_TIMING(cmp_mask);
    }
}