misc decimal

[timotheecour]

performance

for nim-lang#17699, we should have a performance comparison against established decimal128 libraries.

links

• [WIP] Adding Decimal to Std library by JohnAD · Pull Request #17699 · nim-lang/Nim
• mpdecimal — mpdecimal project
  libmpdec - C library
  libmpdec++ - C++ library

Starting from Python-3.3, libmpdec is the basis for Python’s decimal module.

• python3: import decimal

[JohnAD]

A more direct comparison would be with:

http://mongoc.org/libbson/current/index.html

The 'bson' implementation of decimal is the same fixed "bid" 128-bit IEEE 754-2008 standard.

The python version (which is mpdecimal) is a dynamic 32/64/128-bit of a variant of the same standard.

I'm confident both mpdecimal and mongoc are faster at the moment since I've not done any optimization.

(I have freely studied the algorithms from both to help write my library.)

[JohnAD]

Speaking of that; is there any movement to adding 128-bit integers to Nim?

GCC 4.1 and later support __int128_t and __uint128_t along with the relevant ops; at least on 64-bit platforms.

Using 128-bit uint math on the significand (the numbers part) for some of the ops would very likely improve speed quite a bit.

(EDIT)

https://github.com/python/cpython/blob/63298930fb531ba2bb4f23bc3b915dbf1e17e9e1/Modules/_decimal/README.txt

Yeah, I kind of recall this now. If 128 bit support in a 64 bit architecture is detected, mpdecimal totally uses uint128 for the math.