On Tue, Jan 21, 2025 at 2:52 PM Glen Fernandes
I would like to have this PDF on the Boost site somewhere, if there are no objections. I can take care of that and reply with the link.
When people revisit past reviews in the Boost archives: https://lists.boost.org/Archives/boost/2025/01/date.php
If you could do that it would be appreciated although I guess that for at
least next few years my drive link is gonna stay alive.
On Tue, Jan 21, 2025 at 3:14 PM Peter Dimov via Boost
Matt Borland wrote:
Taking decimal types by reference instead of by value - fundamentally the decimalXX types are std::uint32_t, std::uint64_t, and struct { uint64_t hi, uint64_t lo }. I don't think you'll see any performance improvements with those.
Trivially copyable types up to 2*uint64_t in size are passed in registers (on non-Windows x86-64), so pass by reference will be a performance regression, probably a significant one.
If you have time I suggest to read the PDF. I know your time is valuable, but I just think it is faster if we are on same page. In this particular case I tried to be pretty clear in document about this. I was not talking about small types. Also not all functions take 1 argument, in PDF I explicitly used copysign as example. And it *may* be possible that even if decimal128 pass by value is faster decimal128_fast pass by value is not. On Tue, Jan 21, 2025 at 3:36 PM John Maddock via Boost < boost@lists.boost.org> wrote:
It may be worth the experiment, but I'd be surprised if adding a level of indirection is of benefit over passing arguments by value in a couple of registers: possibly there may be benefit for functions accepting many arguments, but I'm assuming there aren't too many of those?
John.
I am a man of data. :) If there are realistic benchmarks saying passing "large" decimals is fine I will believe them. Till then I believe it is not optimal. Also library seems to prefer to pass by reference in certain cases, e.g. contrast this 2 "opposite" functions and their argument types constexpr auto isfinite(decimal128_fast val) noexcept -> bool { #ifndef BOOST_DECIMAL_FAST_MATH return val.significand_.high < detail::d128_fast_inf_high_bits; #else static_cast<void>(val); return true; #endif } constexpr auto not_finite(const decimal128_fast& val) noexcept -> bool { #ifndef BOOST_DECIMAL_FAST_MATH return val.significand_.high >= detail::d128_fast_inf_high_bits; #else static_cast<void>(val); return false; #endif }