Subj : right shifting to divide
To   : comp.programming
From : Rob Somers
Date : Sun Jul 31 2005 10:01 am

Hi, I am reading 'Lion's Commentary on UNIX', and I am wondering about a
small bit of code, which is as follows:

/*
 * Return the arg/128 rounded up.
 */

nseg(n)
{

  return((n+127)>>7);
}

It is found on sheet 16 beginning at line 1768, for anyone who might have
the book.  Anyway, I curious as to the adding of 127 to the number, and
then the right shift.  I realise that it divides the number roughly by two,
but I am still kind of foggy as to the methodology.  Why add 127 then right
shift by 7?  Why not just right shift by 1?

Rob Somers

.