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crypto: Extract some Montgomery helpers out of struct scope #1425

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Merged
chfast merged 1 commit into from
Jan 27, 2026
+16 −15
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crypto: Extract some Montgomery helpers out of struct scope #1425

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31 changes: 16 additions & 15 deletions include/evmmax/evmmax.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,22 @@ constexpr uint64_t inv_mod(uint64_t a) noexcept
return inv;
}

/// Compute the modulus inverse for Montgomery multiplication, i.e., N': mod⋅N' = 2⁶⁴-1.
template <typename UintT>
constexpr uint64_t compute_mont_mod_inv(const UintT& mod) noexcept
{
// Compute the inversion mod[0]⁻¹ mod 2⁶⁴, then the final result is N' = -mod[0]⁻¹
// because this gives mod⋅N' = -1 mod 2⁶⁴ = 2⁶⁴-1.
return -inv_mod(mod[0]);
}

constexpr std::pair<uint64_t, uint64_t> addmul(
uint64_t t, uint64_t a, uint64_t b, uint64_t c) noexcept
{
const auto p = intx::umul(a, b) + t + c;
return {p[1], p[0]};
}
Comment on lines +33 to +47
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Copilot AI Jan 27, 2026

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compute_mont_mod_inv() and addmul() were previously private ModArith helpers but are now free functions in the public evmmax namespace, which expands the public API surface and increases the chance of name collisions (e.g., with other headers that use using namespace evmmax). If these are intended to remain internal implementation details, consider moving them into an internal namespace (e.g. evmmax::detail) or making them static/internal-linkage helpers so they don’t become part of the public API.

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/// The modular arithmetic operations for EVMMAX (EVM Modular Arithmetic Extensions).
template <typename UintT>
class ModArith
Expand All @@ -50,21 +66,6 @@ class ModArith
return intx::udivrem(RR, mod).rem;
}

/// Compute the modulus inverse for Montgomery multiplication, i.e., N': mod⋅N' = 2⁶⁴-1.
static constexpr uint64_t compute_mont_mod_inv(const UintT& mod) noexcept
{
// Compute the inversion mod[0]⁻¹ mod 2⁶⁴, then the final result is N' = -mod[0]⁻¹
// because this gives mod⋅N' = -1 mod 2⁶⁴ = 2⁶⁴-1.
return -inv_mod(mod[0]);
}

static constexpr std::pair<uint64_t, uint64_t> addmul(
uint64_t t, uint64_t a, uint64_t b, uint64_t c) noexcept
{
const auto p = intx::umul(a, b) + t + c;
return {p[1], p[0]};
}

public:
constexpr explicit ModArith(const UintT& mod) noexcept
: mod_{mod}, r_squared_{compute_r_squared(mod)}, mod_inv_{compute_mont_mod_inv(mod)}
Expand Down