EVMMAX: Base C++ API for prototyping #673

chfast · 2023-07-14T10:57:28Z

Add evmmax library with prototype C++ API for Montgomery-based modular arithmetic. This does not implement all aspects of the EVMMAX spec, but is a good starting point for prototyping EVMMAX usage in C++.

See these EIP drafts for more information about EVMMAX:

codecov · 2023-07-14T12:06:50Z

Codecov Report

Merging #673 (5091a79) into master (18a8972) will increase coverage by 0.03%.
Report is 6 commits behind head on master.
The diff coverage is 100.00%.

❗ Current head 5091a79 differs from pull request most recent head babc0b9. Consider uploading reports for the commit babc0b9 to get more accurate results

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@@            Coverage Diff             @@
##           master     #673      +/-   ##
==========================================
+ Coverage   97.41%   97.45%   +0.03%     
==========================================
  Files          81       83       +2     
  Lines        8013     8120     +107     
==========================================
+ Hits         7806     7913     +107     
  Misses        207      207

Flag	Coverage Δ
blockchaintests	`62.95% <ø> (ø)`
statetests	`74.10% <ø> (ø)`
unittests	`94.97% <100.00%> (+0.06%)`	⬆️

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Files Changed	Coverage Δ
lib/evmmax/evmmax.cpp	`100.00% <100.00%> (ø)`
test/unittests/evmmax_test.cpp	`100.00% <100.00%> (ø)`

include/evmmax/evmmax.hpp

axic · 2023-07-16T16:54:50Z

include/evmmax/evmmax.hpp

+    /// Performs a Montgomery modular multiplication. Inputs must be in Montgomery form.
+    uint mul(const uint& x, const uint& y) const noexcept;
+
+    /// Performs a modular addition.


Are these in non-montgomery form? Or for the addition/subtraction implementation it won't matter?

I wonder if we should have another type for the montgomery-form version, like uintmont or montuint.

It doesn't matter.

I've been wondering if we will need ever these operations for non-mont form, but it look that we won't. At least for pairing. BTW silkpre lib does everything using this form.

I will add a comment.

lib/evmmax/evmmax.cpp

rodiazet · 2023-07-17T10:46:12Z

include/evmmax/evmmax.hpp

+    /// Performs a Montgomery modular multiplication. Inputs must be in Montgomery form.
+    uint mul(const uint& x, const uint& y) const noexcept;
+
+    /// Performs a modular addition.


I've been wondering if we will need ever these operations for non-mont form, but it look that we won't. At least for pairing. BTW silkpre lib does everything using this form.

include/evmmax/evmmax.hpp

lib/evmmax/evmmax.cpp

gumb0 · 2023-07-31T10:30:22Z

lib/evmmax/evmmax.cpp

+template <typename UintT>
+UintT ModArith<UintT>::to_mont(const UintT& x) const noexcept
+{
+    return mul(x, m_r_squared);


Isn't Montgomery form aR mod N and not aR² mod N ?

True, but mul is actually mont_mul which is abR⁻¹ mod N. Therefore: mul(a, R²) is aR²R⁻¹ mod N is aR mod N.

I will add a comment.

Montgomery reduction of an input a yields aR**-1 mod N. So to convert a to Montgomery form, R² is passed and the extra factor of R cancels out.

oh I see! missed that it calls Montgoemry multiplication. Why not call it mont_mul() ?

The internal representation (e.g. Montgomery form) is abstracted away in EVMMAX. The multiplication is just MULMODX. But to_mont() and from_mont() maps to LOADX and STOREX. Here we started with add, sub and mul, but we don't have proper load, store yet.

gumb0 · 2023-07-31T12:55:37Z

lib/evmmax/evmmax.cpp

+{
+namespace
+{
+inline constexpr uint64_t mul_inv64(uint64_t base) noexcept


Can you explain this too? what does it calculate and what's the forumla?

Also, why is used only with 1 word of modulus.

I don't know exactly. I copied it from somewhere. But this is some Montgomery multiplication magic. I'm guessing this is R⁻¹ mod N but only most significant bits are needed.

Ok, this is used to compute "Integer N′ in [0, B − 1] such that NN′ ≡ −1 (mod B)" where B is 2^64. This loop looks like exponentiation with exponent being −1 (mod B) i.e. 2^64-1.

gumb0 · 2023-07-31T13:30:00Z

lib/evmmax/evmmax.cpp

+    const auto s = d.value + mod;
+    return (d.carry) ? s : d.value;


This could calculate s only when needed

Suggested change

const auto s = d.value + mod;

return (d.carry) ? s : d.value;

return d.carry ? (d.value + mod) : d.value;

This is done this way on purpose to follow branchless implementation.

gumb0 · 2023-07-31T13:50:30Z

test/unittests/evmmax_test.cpp

+
+template <typename>
+class evmmax_test : public testing::Test
+{};


Suggestion if possible: alias inside fixture class TypeParam as ModA or something close to ModArith.

Maybe also could have an instance of it as class member.

There are some limitations to this. Either you need to use this-> or TestFixture::. http://google.github.io/googletest/reference/testing.html#TYPED_TEST

lib/evmmax/evmmax.cpp

Add evmmax library with prototype C++ API for Montgomery-based modular arithmetic. This does not implement all aspects of the EVMMAX spec, but is a good starting point for prototyping EVMMAX usage in C++.

chfast force-pushed the evmmax_base branch 4 times, most recently from 1884473 to 6789e2e Compare July 15, 2023 20:54

chfast marked this pull request as ready for review July 15, 2023 20:55

chfast force-pushed the evmmax_base branch from d901cb1 to 0833a5b Compare July 16, 2023 16:48

axic reviewed Jul 16, 2023

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chfast force-pushed the evmmax_base branch from 1b08460 to dcb0d1e Compare July 28, 2023 09:32

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chfast force-pushed the evmmax_base branch 2 times, most recently from 2d24c2d to 6dc5877 Compare July 31, 2023 14:47

evmmax: Add modular arithmetic API for EVMMAX

e7e1345

Add evmmax library with prototype C++ API for Montgomery-based modular arithmetic. This does not implement all aspects of the EVMMAX spec, but is a good starting point for prototyping EVMMAX usage in C++.

chfast added 2 commits July 31, 2023 17:59

test: Add evmmax/ModArith unit tests

5e28b98

bench: Add evmmax/ModArith benchmarks for uint256

7f8d549

chfast force-pushed the evmmax_base branch from 6dc5877 to 7f8d549 Compare July 31, 2023 15:59

chfast merged commit eda0beb into master Jul 31, 2023
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chfast deleted the evmmax_base branch July 31, 2023 16:31

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EVMMAX: Base C++ API for prototyping #673

EVMMAX: Base C++ API for prototyping #673

chfast commented Jul 14, 2023 •

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codecov bot commented Jul 14, 2023 •

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axic Jul 16, 2023

axic Jul 16, 2023

chfast Jul 16, 2023

rodiazet Jul 17, 2023

chfast Jul 28, 2023

rodiazet Jul 17, 2023

gumb0 Jul 31, 2023

chfast Jul 31, 2023

jwasinger Jul 31, 2023

gumb0 Jul 31, 2023

chfast Jul 31, 2023

gumb0 Jul 31, 2023

chfast Jul 31, 2023

chfast Jul 31, 2023

gumb0 Jul 31, 2023

chfast Jul 31, 2023

gumb0 Jul 31, 2023

gumb0 Jul 31, 2023

chfast Jul 31, 2023

		const auto s = d.value + mod;
		return (d.carry) ? s : d.value;

	const auto s = d.value + mod;
	return (d.carry) ? s : d.value;
	return d.carry ? (d.value + mod) : d.value;

EVMMAX: Base C++ API for prototyping #673

EVMMAX: Base C++ API for prototyping #673

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chfast commented Jul 14, 2023 •

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