Bench of integer concats

int-concat.cc

#include "time.h"
#include "math.h"
#include "assert.h"
#include <string>

// After http://ideone.com/hbWgE

int num_tests = 5000000;

unsigned duck(unsigned x, unsigned y) {
    unsigned pow = 10;
    while(y >= pow)
        pow *= 10;
    return x * pow + y;
}
int myPow(int x, int p)
{
     if (p == 0) return 1;
     if (p == 1) return x;

     int tmp = myPow(x, p/2);
     if (p%2 == 0) return tmp * tmp;
     else return x * tmp * tmp;
}
int david(int x, int y) {
    int power = log10(y);
    return x*myPow(10,power+1)+y;
}

int drummer(int x, int y) {
    int digits = log10(y)+1;
    int shifted = x * pow(10, digits);   // will be 1100 in your example
    return shifted + y;   // 1111
}

int shabeer(int x, int y) {
    int temp=0;
    int z=x;
    while(y>0)
    {
        // take reciprocal of y into temp
        temp=(temp*10)+(y%10);
        y=y/10;
    }
    while(temp>0)
    {
        // take each number from last of temp and add to last of z
        z=(z*10)+(temp%10);
        temp=temp/10;
    }
    return z;
}

int gokcehan(int x, int y) {
    int temp = y;
    while (y != 0) {
        x *= 10;
        y /= 10;
    }
    return x + temp;
}

int naive(int x, int y) {
  return std::stol(std::to_string(x) + std::to_string(y));
}

int stupid(int x, int y) {
  char buf[16];
  snprintf(buf, sizeof(buf), "%i%i", x, y);
  return std::stol(buf);
}

void int_time(const char* name, int(*func)(int, int)) {
    clock_t start = clock();
    int r = 0;
    int i = 0;
    for(; i<num_tests; ++i)
        r += func(i, i);
    printf("%s found %u in %d\n", name, r, clock()-start);
}

void uint_time(const char* name, unsigned(*func)(unsigned, unsigned)) {
    clock_t start = clock();
    unsigned r = 0;
    unsigned i = 0;
    for(; i<num_tests; ++i)
        r += func(i, i);
    printf("%s found %u in %d\n", name, r, clock()-start);
}

void uint_accuracy(const char* name, unsigned(*func)(unsigned, unsigned)) {
    printf("testing %s accuracy: ", name);
    assert(func(0, 0) == 0);
    assert(func(0, 1) == 1);
    assert(func(0, 10) == 10);
    assert(func(1, 0) == 10);
    assert(func(1, 1) == 11);
    assert(func(1, 10) == 110);
    assert(func(10, 0) == 100);
    assert(func(10, 1) == 101);
    assert(func(10, 10) == 1010);
    assert(func(23, 456) == 23456);
    assert(func(234, 56) == 23456);
    printf("pass\n");
}

void int_accuracy(const char* name, int(*func)(int, int)) {
    printf("testing %s accuracy: ", name);
    assert(func(0, 0) == 0);
    assert(func(0, 1) == 1);
    assert(func(0, 10) == 10);
    assert(func(1, 0) == 10); //several fail this one
    assert(func(1, 1) == 11);
    assert(func(1, 10) == 110);
    assert(func(10, 0) == 100); //several fail this one
    assert(func(10, 1) == 101);
    assert(func(10, 10) == 1010);
    assert(func(23, 456) == 23456);
    assert(func(234, 56) == 23456);
    printf("pass\n");
}

int main() {
    uint_time("duck", duck);
    uint_time("duck", duck);
    int_time("david", david);
    int_time("david", david);
    int_time("drummer", drummer);
    int_time("drummer", drummer);
    int_time("shabeer", shabeer);
    int_time("shabeer", shabeer);
    int_time("gokcehan", gokcehan);
    int_time("gokcehan", gokcehan);
    int_time("stupid", stupid);
    int_time("stupid", stupid);
    int_time("naive", stupid);
    int_time("naive", stupid);
    uint_accuracy("duck", duck);
    //int_accuracy("gokcehan", gokcehan); //Assertion `func(1, 0) == 10' failed.
    //int_accuracy("drummer", drummer); //Assertion `func(1, 0) == 10' failed.
    //int_accuracy("david", david); //Assertion `func(1, 0) == 10' failed.
    //int_accuracy("shabeer", shabeer); //Assertion `func(0, 10) == 10' failed.
    return 0;
}

output

duck found 2343525334 in 54586
duck found 2343525334 in 54567
david found 2343525334 in 230050
david found 2343525334 in 229112
drummer found 3188974518 in 306875
drummer found 3188974518 in 306296
shabeer found 2299299461 in 790372
shabeer found 2299299461 in 786956
gokcehan found 2343525334 in 212261
gokcehan found 2343525334 in 217507
stupid found 2343525334 in 1543151
stupid found 2343525334 in 1504988
naive found 2343525334 in 1497291
naive found 2343525334 in 1513641
testing duck accuracy: pass