# Late request for additional functions

This page is part of the web mail archives of SRFI 33 from before July 7th, 2015. The new archives for SRFI 33 contain all messages, not just those from before July 7th, 2015.

```Olin (and others):

I was looking at iterative bignum algorithms for calculating pi and other
things last week.  In such algorithms, one would like to say: stop the
general iteration if two approximations a and b, each of length n bits,
agree to at least their most significant n/2 bits (then you execute a
cleanup operation).  One would like to do this without actually subtracting
the two numbers, which generally leads to n bits of garbage.  This is a fairly
common operation in iterative algorithms for integer division, square root,
etc., and algebraic-geometric mean (AGM) algorithms.

So I propose two new functions (modulo naming)

(least-significant-bit-difference a b) => a number or #f
(most-significant-bit-difference a b)  => a number or #f

The first function would return the location (index) of the least
significant bit that was different between the two integers, or #f
if a and b are equal.

The second function would return the location (index) of the most
significant bit that was different between the two integers, or #f
if one of a and b is nonnegative and the other is negative.