Re: [Boost-bugs] [Boost C++ Libraries] #9233: Suboptimal shift by multiples of 8 bits

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #9233: Suboptimal shift by multiples of 8 bits
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2016-02-26 10:19:04

#9233: Suboptimal shift by multiples of 8 bits
  Reporter: psiha | Owner: johnmaddock
      Type: Bugs | Status: closed
 Milestone: To Be Determined | Component: multiprecision
   Version: Boost 1.54.0 | Severity: Optimization
Resolution: wontfix | Keywords:

Comment (by psiha):

 Replying to [comment:3 johnmaddock]:
> Fixed in

 Thanks John :)
 I no longer use/need this functionality so I didn't test but from a
 cursory skim it looks good...except that maybe the (little) endian checks
 are not really necessary: if you make them in only one place - where you
 decide on the underlying/raw/limb layout - if you order the limbs in
 'machine endianess' (I'm guessing) the rest of the code can be endianness
 agnostic (and more readily assume correct byte ordering/use
 memcpy/move/set more easily)...

> It turns out that memmove is (very slightly) faster than moving whole
 limbs so that's the preferred method when available.

 It's also smaller (one call instead of a loop for every instantiation;)

> Limbs are half the size of the largest available integers - so 32-bit
 for msvc as there's no 128-bit integer support (unlike mingw for example).

 Thanks for the explanation ;)

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