[boost] Multiprecision vs. xint

Subject: [boost] Multiprecision vs. xint
From: Phil Endecott (spam_from_boost_dev_at_[hidden])
Date: 2012-06-15 07:27:13

Dear All,

I'd like to encourage people who are looking at the proposed 
Multiprecision library to remind themselves of the xint review last 
year.  See e.g.

   http://thread.gmane.org/gmane.comp.lib.boost.devel/218624  (result)
   http://thread.gmane.org/gmane.comp.lib.boost.devel/215968  (my review)
   etc. etc.

To what extent do we believe that this new library addresses the 
weaknesses of the last proposal?

It would be great if Vladimir Prus, review manager for xint, could 
write a review of Multiprecision.

Here's my take on it:

Multiprecision addresses many of the problems of xint, and also extends 
the scope into areas that xint did not address at all.  However it 
still suffers some of the same problems: if I want an int128_t that is 
just 128 bits of data, it doesn't help me.  Furthermore, it doesn't 
help me to build the int128_t that I want.  Although Multiprecision is 
divided into "front" and "back"-ends, this division is not in the right 
place to let me substitute my own backend that just provides the 128 
bits of storage.  In the xint reviews, we suggested that the algorithms 
should be decoupled from the data structures and the same applies 
here.  Similarly, this implementation doesn't provide hooks that would 
allow me to substitute e.g. assembler implementations of the algorithms.

Regards,  Phil.