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Subject: Re: [boost] Looking for some "real world" extended precision integer arithmetic tests
From: Andrii Sydorchuk (sydorchuk.andriy_at_[hidden])
Date: 2012-01-27 06:14:55

> What you have is a variable precision type using fixed storage?

Yes you are right. However the functionality it provides is the same as
with 2's complement backend.
The reasons 2's complement representation is used for integral types
(int32, int64) are:
1) it requires less storage, as doesn't use additional value to handle
number of bits set.
2) it allows to execute addition and subtraction quickly on CPU (without
considering different sign cases). For higher order fixed_int this speedup
won't be notable, as you spend more time on adding limbs and doing shifts.

Certainly looks like lazy evaluation of higher-order limbs is a big win in
> this case - I'm guessing that most operations use only one or two limbs,
> and just every now and then you get a true big number?

Correct. That's why I keep insisting on the implementation from here>.
Wrapping it with a multiprecision interface will make it a very good bigint
library I believe. However before doing that we should also investigate
concerns around that library (I'll try to contact the author).


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