Re: [multiprecision] Getting the best performance on windows for uint128_t etc

From: degski (degski_at_[hidden])
Date: 2019-07-12 08:12:10

On Fri, 12 Jul 2019 at 10:38, John Maddock via Boost-users <
boost-users_at_[hidden]> wrote:

> Aside: adding a native population count function might well be a useful
> addition to the library...
>

Native clz/ctz (_BitScanReverse/_BitScanForward) might be useful as well.

> The limb size is always half the width of the largest compiler supported
> integer type - this is a necessary condition to implement arithmetic
> entirely within the language.
>

This seems a high price to pay [I guess the 'within the language' is key
here]. At some point in time [when 64-bit started to be a general thing]
there was some info regarding this on gmplib.org, which basically stated
that 64-bit limbs [on x64] were 4 times faster than 32-bit limbs. GMP
(MPIR) does 64-bit limbs on Windows, no problem [but yes it's C].

If clang-win can have __int128 support enabled

clang-cl can/will have __int128 support enabled by passing it '-Xclang
-fforce-enable-int128', i.e. pass '-fforce-enable-int128' to clang++.

degski
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