#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <inttypes.h>

uint32_t multiply (uint16_t a, uint16_t b)
{
  //uint16_t mask = 0b0000000000000001;

  register uint32_t result = 0;

    result += (a &  ( (int16_t)( ( b & (1 << 0) ) << 15 ) ) / ( 1 << 15) ) << 0;


    result += (a &  ( (int16_t)( ( b & (1 << 1) ) << 14 ) ) / ( 1 << 15) ) << 1;


    result += (a &  ( (int16_t)( ( b & (1 << 2) ) << 13 ) ) / ( 1 << 15) ) << 2;


    result += (a &  ( (int16_t)( ( b & (1 << 3) ) << 12 ) ) / ( 1 << 15) ) << 3;


    result += (a &  ( (int16_t)( ( b & (1 << 4) ) << 11 ) ) / ( 1 << 15) ) << 4;


    result += (a &  ( (int16_t)( ( b & (1 << 5) ) << 10 ) ) / ( 1 << 15) ) << 5;


    result += (a &  ( (int16_t)( ( b & (1 << 6) ) << 9  ) ) / ( 1 << 15) ) << 6;


    result += (a &  ( (int16_t)( ( b & (1 << 7) ) << 8  ) ) / ( 1 << 15) ) << 7;


    result += (a &  ( (int16_t)( ( b & (1 << 8) ) << 7  ) ) / ( 1 << 15) ) << 8;


    result += (a &  ( (int16_t)( ( b & (1 << 9) ) << 6  ) ) / ( 1 << 15) ) << 9;


    result += (a &  ( (int16_t)( ( b & (1 <<10) ) << 5  ) ) / ( 1 << 15) ) << 10;


    result += (a &  ( (int16_t)( ( b & (1 <<11) ) << 4  ) ) / ( 1 << 15) ) << 11;


    result += (a &  ( (int16_t)( ( b & (1 <<12) ) << 3  ) ) / ( 1 << 15) ) << 12;


    result += (a &  ( (int16_t)( ( b & (1 <<13) ) << 2  ) ) / ( 1 << 15) ) << 13;


    result += (a &  ( (int16_t)( ( b & (1 <<14) ) << 1  ) ) / ( 1 << 15) ) << 14;


    result += (a &  ( (int16_t)( ( b & (1 <<15) ) << 0  ) ) / ( 1 << 15) ) << 15;
  return result;
}

int main(void)
{

  uint16_t a, b;
  a = 0;
  b = 0;

  do
  {
    if (multiply(a, b) != a * b)


      fprintf(stderr,
               "ERROR:\n"
               "my: %u\n"
               "norm: %u\n"
               "%hu * %hu\n"
               "\n",
               multiply(a, b), (a * b),a, b
             );

    if (UINT16_MAX == a)
    {
      b++;
    }
    a++;
  //fprintf(stderr, "%hu * %hu\n", a, b);
  } while ( ( a != 0 ) || (b != 0) );

  fprintf(stderr, "%"PRIu16"* ""%"PRIu16"\n", a, b);
  printf("Done!\n");

  return 0;
}
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <inttypes.h>

uint32_t multiply (uint16_t a, uint16_t b)
{
  //uint16_t mask = 0b0000000000000001;

  register uint32_t result = 0;

    result += (a &  ( (int16_t)( ( b & (1 << 0) ) << 15 ) ) / ( 1 << 15) ) << 0;


    result += (a &  ( (int16_t)( ( b & (1 << 1) ) << 14 ) ) / ( 1 << 15) ) << 1;


    result += (a &  ( (int16_t)( ( b & (1 << 2) ) << 13 ) ) / ( 1 << 15) ) << 2;


    result += (a &  ( (int16_t)( ( b & (1 << 3) ) << 12 ) ) / ( 1 << 15) ) << 3;


    result += (a &  ( (int16_t)( ( b & (1 << 4) ) << 11 ) ) / ( 1 << 15) ) << 4;


    result += (a &  ( (int16_t)( ( b & (1 << 5) ) << 10 ) ) / ( 1 << 15) ) << 5;


    result += (a &  ( (int16_t)( ( b & (1 << 6) ) << 9  ) ) / ( 1 << 15) ) << 6;


    result += (a &  ( (int16_t)( ( b & (1 << 7) ) << 8  ) ) / ( 1 << 15) ) << 7;


    result += (a &  ( (int16_t)( ( b & (1 << 8) ) << 7  ) ) / ( 1 << 15) ) << 8;


    result += (a &  ( (int16_t)( ( b & (1 << 9) ) << 6  ) ) / ( 1 << 15) ) << 9;


    result += (a &  ( (int16_t)( ( b & (1 <<10) ) << 5  ) ) / ( 1 << 15) ) << 10;


    result += (a &  ( (int16_t)( ( b & (1 <<11) ) << 4  ) ) / ( 1 << 15) ) << 11;


    result += (a &  ( (int16_t)( ( b & (1 <<12) ) << 3  ) ) / ( 1 << 15) ) << 12;


    result += (a &  ( (int16_t)( ( b & (1 <<13) ) << 2  ) ) / ( 1 << 15) ) << 13;


    result += (a &  ( (int16_t)( ( b & (1 <<14) ) << 1  ) ) / ( 1 << 15) ) << 14;


    result += (a &  ( (int16_t)( ( b & (1 <<15) ) << 0  ) ) / ( 1 << 15) ) << 15;
  return result;
}

int main(void)
{

  uint16_t a, b;
  a = 0;
  b = 0;

  do
  {
    if (multiply(a, b) != a * b)


      fprintf(stderr,
               "ERROR:\n"
               "my: %u\n"
               "norm: %u\n"
               "%hu * %hu\n"
               "\n",
               multiply(a, b), (a * b),a, b
             );

    if (UINT16_MAX == a)
    {
      b++;
    }
    a++;
  //fprintf(stderr, "%hu * %hu\n", a, b);
  } while ( ( a != 0 ) || (b != 0) );

  fprintf(stderr, "%"PRIu16"* ""%"PRIu16"\n", a, b);
  printf("Done!\n");

  return 0;
}