Re: [Boost-users] About naming of integer log in base 2

Subject: Re: [Boost-users] About naming of integer log in base 2
From: Paul A. Bristow (pbristow_at_[hidden])
Date: 2010-07-15 07:22:44

From: boost-users-bounces_at_[hidden] [mailto:boost-users-bounces_at_[hidden]] On Behalf Of Murilo Adriano
Vasconcelos
Sent: Wednesday, July 14, 2010 9:04 PM
To: boost-users_at_[hidden]
Subject: [Boost-users] About naming of integer log in base 2

 

Hi all,

 

I implemented a function [0] wich computes the logarithm in base two of integers and want to know what naming is most
appropriated:

 

ilog2

or simply

log2

 

[0] - http://svn.boost.org/svn/boost/sandbox/SOC/2010/bits_and_ints/boost/integer/ilog2.hpp

 

My instinct is for log2 so it might be specialised for floating point too.

 

Glancing at your code, I note you don't explicitly check that type T is integer (but perhaps is_signed does that?)

 

But I feel that 
 
 *     If `value` is equal to 0, the value returned is undefined

 

may be evil in some peoples opinion.

 

Of course it is always a vexed question what to do for the corner cases like this.  I am sure that this sort of issue
will raise its ugly head for other functions.

 

You might like to consider making problem cases 'policy controlled'.

 

In the Boost.Math package John Maddock went to the trouble of providing a way of letting users controlling what happens
for cases like this.

 

(He retrofitted policies, so you don't have to do it immediately - but doing it will focus your mind on the possible
corner cases).

 

If you read the math docs, perhaps the pdf at

 

http://boost.cowic.de/rc/pdf/math.pdf

 

or the download from source,

 

and see the section on Policies you will see what it being suggested, and some examples.

 

You might return zero, or ? or throw an exception?

 

You can consult and see if there is a consensus on the default policy.  

 

At least it may reduce the discussion (Boosters are really good at that ;-) on what *should* happen, if you can say "You
*can* make it do what you want."

 

Paul

 

 

---
Paul A. Bristow
Prizet Farmhouse
Kendal, UK   LA8 8AB
[phone], mobile [phone]
pbristow_at_[hidden]