multiplication rapide - Page 1

#include <stdio.h>
#include <conio.h>

#define abso(X) (X>0?X:-X)

void main()
{
int i;
char *var="variable",op,*shift="<<";
int num,roll[]={1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,131072,262144,524288,1048576,2097152,4194304};
clrscr();
printf("operation a faire?(VAR * NB ou VAR / NB):")
scanf("%s %c %d",var,&op,&num);
if(op=='/')shift=">>";
while(num)
{
 for(i=0;i<22;i++)
  {
	if(abso(num)==roll[i])
	{
	 //printf("%d est egal … %d",num,roll[i]);
	 if(num>0)
		{
		 num-=roll[i];
		 printf("+(%s%s%d)",var,shift,i);
		}
		else
		{
		 num+=roll[i];
		 printf("-(%s%s%d)",var,shift,i);
		}
	 break;

	}
	if((abso(num)>roll[i])&&(abso(num)<roll[i+1]))
	{
	 //printf("non est bien entre %d  et %d",roll[i],roll[i+1]);
	 if((roll[i+1]-abso(num))>(roll[i]-abso(num)))
	 {
		//printf("n%d est plus pres",roll[i+1]);
		if(num>0)
		{
		 num-=roll[i+1];
		 printf("+(%s%s%d)",var,shift,i+1);
		}
		else
		{
		 num+=roll[i+1];
		 printf("-(%s%s%d)",var,shift,i+1);
		}
	 }
	 else
	 {
		//printf("n%d est plus pres",roll[i]);
		if(num>0)
		{
		 num-=roll[i];
		 printf("+(%s%s%d)",var,shift,i);
		}
		else
		{
		 num+=roll[i];
		 printf("-(%s%s%d)",var,shift,i);
		}
	 }
	 }
	}
}
getch();
}