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perf: optimize division to uint32 to make re-target-pow calculation much faster #7352

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perf: optimize division to uint32 to make re-target-pow calculation much faster #7352

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de1e56a
perf: optimize division to uint32 to make re-target-pow calculation m…
knst Jun 9, 2026
e8435d3
test: add regression test for faster division of base_uint<256> to ui…
knst Jun 9, 2026
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18 changes: 18 additions & 0 deletions src/arith_uint256.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@

#include <arith_uint256.h>

#include <limits>
#include <uint256.h>
#include <crypto/common.h>

Expand Down Expand Up @@ -72,6 +73,23 @@ base_uint<BITS>& base_uint<BITS>::operator*=(const base_uint& b)
return *this;
}

template <unsigned int BITS>
base_uint<BITS>& base_uint<BITS>::operator/=(uint64_t b32)

@UdjinM6 UdjinM6 Jun 10, 2026

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nit: is it a typo?

Suggested change
base_uint<BITS>& base_uint<BITS>::operator/=(uint64_t b32)
base_uint<BITS>& base_uint<BITS>::operator/=(uint64_t b64)

same in other places

@knst knst Jun 11, 2026 •
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not really a typo, because it's supposed optimized for b32 only. If you think that's confusing I'd rename it.

It is supposed to be uint32_t b32 but compiler won't say a word if that's called with uint64_t, so, I keep it mixed.

{
if (b32 == 0)
throw uint_error("Division by zero");
if (b32 > std::numeric_limits<uint32_t>::max()) {
return *this /= base_uint(b32);
}
uint64_t rem = 0;
for (int i = WIDTH - 1; i >= 0; --i) {
uint64_t cur = (rem << 32) | pn[i];
pn[i] = static_cast<uint32_t>(cur / b32);
rem = cur % b32;
}
return *this;
}

template <unsigned int BITS>
base_uint<BITS>& base_uint<BITS>::operator/=(const base_uint& b)
{
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2 changes: 2 additions & 0 deletions src/arith_uint256.h
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Original file line number Diff line number Diff line change
Expand Up @@ -158,6 +158,7 @@ class base_uint

base_uint& operator*=(uint32_t b32);
base_uint& operator*=(const base_uint& b);
base_uint& operator/=(uint64_t b32);
base_uint& operator/=(const base_uint& b);

base_uint& operator++()
Expand Down Expand Up @@ -207,6 +208,7 @@ class base_uint
friend inline base_uint operator>>(const base_uint& a, int shift) { return base_uint(a) >>= shift; }
friend inline base_uint operator<<(const base_uint& a, int shift) { return base_uint(a) <<= shift; }
friend inline base_uint operator*(const base_uint& a, uint32_t b) { return base_uint(a) *= b; }
friend inline base_uint operator/(const base_uint& a, uint64_t b) { return base_uint(a) /= b; }
friend inline bool operator==(const base_uint& a, const base_uint& b) { return memcmp(a.pn, b.pn, sizeof(a.pn)) == 0; }
friend inline bool operator!=(const base_uint& a, const base_uint& b) { return memcmp(a.pn, b.pn, sizeof(a.pn)) != 0; }
friend inline bool operator>(const base_uint& a, const base_uint& b) { return a.CompareTo(b) > 0; }
Expand Down
13 changes: 13 additions & 0 deletions src/test/arith_uint256_tests.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -361,6 +361,19 @@ BOOST_AUTO_TEST_CASE( divide )
BOOST_CHECK(R2L / MaxL == ZeroL);
BOOST_CHECK(MaxL / R2L == 1);
BOOST_CHECK_THROW(R2L / ZeroL, uint_error);

// The integer-divisor overload must be bit-identical to dividing by the same
// value widened to arith_uint256, for both the fast word-wise path
// (<= uint32 max) and the arith_uint256 fallback above it.
for (uint64_t d : {uint64_t{1}, uint64_t{2}, uint64_t{24}, uint64_t{3600},
uint64_t{std::numeric_limits<uint32_t>::max()},
uint64_t{std::numeric_limits<uint32_t>::max()} + 1,
uint64_t{0xFEDCBA9876543210}}) {
BOOST_CHECK(R1L / d == R1L / arith_uint256(d));
BOOST_CHECK(R2L / d == R2L / arith_uint256(d));
BOOST_CHECK(MaxL / d == MaxL / arith_uint256(d));
}
BOOST_CHECK_THROW(R1L / uint64_t{0}, uint_error);
}


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