cpy-vs-cat.c

// clang -std=c99 -O3 cpy-vs-cat.c
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <mach/mach_time.h>

const int e6 = 1000000;
#define repeat for(int j = 0; j < e6; j++)
void flush() { fflush(stdout); }

int main() {
    double pcat = 1.0/0;
    for(size_t sz = 0; sz < 1 << 20; sz += sz, sz += 1024*!sz) {

        printf("10⁶×%9zu b", sz), flush();
        char* to = calloc(2*sz+1, sizeof(char));
        char* from = calloc(sz+1, sizeof(char));
        memset(to, 1, sz);
        memset(from, 1, sz);
        printf(" ⇒  "), flush();

        uint64_t t = mach_absolute_time(); // nsec
        repeat { strcat(to, from); to[sz] = 0; }
        double dcat = (mach_absolute_time() - t) / e6; // msec
        printf("%9.1f (×%.0f) : ", dcat, dcat/pcat), flush();

        t = mach_absolute_time();
        repeat { memcpy(to + sz, from, sz+1); }
        double dcpy = (double)((mach_absolute_time() - t)) / e6;
        printf("%9.1f, cat = %.3f cpy)\n", dcpy, dcat/dcpy);

        free(from), free(to);
        pcat = dcat;
    }
}

/* rmpb14
10⁶×        0 b ⇒       18.0 (×0) :       3.9, cat = 4.613 cpy)
10⁶×     1024 b ⇒      114.0 (×6) :      16.3, cat = 6.984 cpy)
10⁶×     2048 b ⇒      190.0 (×2) :      34.0, cat = 5.588 cpy)
10⁶×     4096 b ⇒      342.0 (×2) :      52.2, cat = 6.552 cpy)
10⁶×     8192 b ⇒      630.0 (×2) :     117.6, cat = 5.355 cpy)
10⁶×    16384 b ⇒     1694.0 (×3) :     193.5, cat = 8.754 cpy)
10⁶×    32768 b ⇒     3644.0 (×2) :    1351.9, cat = 2.695 cpy)
10⁶×    65536 b ⇒     7561.0 (×2) :    2690.4, cat = 2.810 cpy)
10⁶×   131072 b ⇒    16877.0 (×2) :    5391.1, cat = 3.131 cpy)
10⁶×   262144 b ⇒    36838.0 (×2) :   13533.8, cat = 2.722 cpy)
10⁶×   524288 b ⇒    77799.0 (×2) :   29948.5, cat = 2.598 cpy)
*/