Re: Counting bits

[rarachel@prism.poly.edu (Arsen Ray Arachelian)]

Why bother when you can simply do an eight line function?

int bitcount(char b)
{
register int retval=0;

 if (a & 1) retval++;
 if (a & 2) retval++;
 if (a & 4) retval++;
 if (a & 8) retval++;
 if (a & 16) retval++;
 if (a & 32) retval++;
 if (a & 64) retval++;
 if (a & 128) retval++; 

return retval;
}

This function, (if you have a decent compiler) will be turned into about 32
instructions at most.  IE:
  MOV BL,00
  MOV AL,value_of_a_wherever_that_may_be_in_the_stack
  AND AL,01
  JZ @+2_instructions
  INC BL
  AND AL,02
  JZ @+2_instructions...
  ad compiler nausea.

Simple, no shifting, no adding, no dividing, and best of all, it's straight
forward, and you don't have the possibility of sneaking in bugs.  Whereas
the previous example is a one liner, and may be shorter, it will be far
harder for humans to understand. :-)


Just my two bits. ;^)