uint256: optimize Mod, DivMod, AddMod

[AaronChen0]

Lt is branchless and can be inlined, while Cmp has two if branches and can not be inlined. So Lt is better.

To check if a simple function can be inlined or not in golang, run

go build -gcflags='-m -m' |& grep Lt

Learn this trick a few days ago.

Benchmark

goos: linux
goarch: amd64
pkg: github.com/holiman/uint256
cpu: AMD Ryzen 7 7735H with Radeon Graphics         
                         │     old     │                 new                 │
                         │   sec/op    │   sec/op     vs base                │
Mod/small/uint256-16       4.041n ± 2%   2.865n ± 1%  -29.10% (p=0.000 n=10)
Mod/mod64/uint256-16       22.68n ± 1%   21.39n ± 2%   -5.69% (p=0.000 n=10)
Mod/mod128/uint256-16      39.82n ± 1%   38.23n ± 1%   -4.01% (p=0.000 n=10)
Mod/mod192/uint256-16      36.37n ± 1%   34.69n ± 2%   -4.62% (p=0.000 n=10)
Mod/mod256/uint256-16      28.33n ± 1%   27.08n ± 1%   -4.39% (p=0.000 n=10)
DivMod/small/uint256-16    4.445n ± 1%   3.121n ± 3%  -29.80% (p=0.000 n=10)
DivMod/mod64/uint256-16    22.95n ± 1%   22.12n ± 2%   -3.64% (p=0.000 n=10)
DivMod/mod128/uint256-16   40.21n ± 2%   39.35n ± 0%   -2.16% (p=0.001 n=10)
DivMod/mod192/uint256-16   36.58n ± 2%   35.75n ± 1%   -2.26% (p=0.000 n=10)
DivMod/mod256/uint256-16   28.75n ± 1%   27.68n ± 2%   -3.70% (p=0.000 n=10)
AddMod/small/uint256-16    6.158n ± 2%   4.748n ± 0%  -22.90% (p=0.000 n=10)
AddMod/mod64/uint256-16    9.024n ± 2%   7.413n ± 1%  -17.86% (p=0.000 n=10)
AddMod/mod128/uint256-16   18.00n ± 2%   15.86n ± 1%  -11.89% (p=0.000 n=10)
AddMod/mod192/uint256-16   19.78n ± 2%   17.61n ± 2%  -10.97% (p=0.000 n=10)
AddMod/mod256/uint256-16   6.416n ± 2%   6.422n ± 1%        ~ (p=0.928 n=10)
geomean                    16.63n        14.84n       -10.76%

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (70cbe2b) to head (1d336e5).

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #173   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            5         5           
  Lines         1632      1628    -4     
=========================================
- Hits          1632      1628    -4     

[holiman]

LGTM

[holiman]

Well done!