;****************************************************************************
; LISTING 1 - DECIMAL-TO-BINARY CONVERSION IN C
;
; "C Routine speeds decimal-to-binary conversion," EDN, Nov 24, 1999, pg 170
; http://www.ednmag.com/ednmag/reg/1999/112499/designideas.htm#24di3
;****************************************************************************

/* 
   Fast decimal-to-binary conversions
   Author: Giovanni Motta (gim@ieee.org) 
*/
#include <stdio.h>
int c[32];

/* 
   Decimal to binary 
*/
void fast_d2b(unsigned long x, int * c) {
   int i;

   for(i=0;i<32;i++)
      *(c++) = (x >> i) & 0x1;
}

/* 
   Binary to decimal 
*/
void fast_b2d(unsigned long int * n, int * c) {
   int i = 32;

   *n = 0;
   while(i--) {
      *n <<= 1;
      *n += *(c+i);
   }
}

main() {
   int k; 
   unsigned long int x,  y;

   printf("\nEnter an integer number");
   printf(" smaller than 4,294,967,296 : ");
   scanf("%lu", &x);
   printf("\nCalling fast_d2b for ");
   printf("decimal to binary conversion :\n");
   fast_d2b(x, c);
   printf("   Bin # =");
   for (k=31; k>=0; k--)
      printf(" %d",c[k]);
   printf("\n\nCalling fast_b2d for ");
   printf("binary to decimal conversion :\n");
   fast_b2d(&y, c);
   printf("   Dec # = %lu\n", y);
   return 0;      
}