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benchmark: Add more less-than implementations #277

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Dec 11, 2022
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benchmark: Add more less-than implementations #277

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43 changes: 43 additions & 0 deletions test/benchmarks/benchmarks.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -358,6 +358,18 @@ BENCHMARK_TEMPLATE(shift, uint512, uint64_t, shl_public)->DenseRange(-1, 3);
return subc(x, y).carry;
}

[[gnu::noinline]] static bool lt_split(const uint256& x, const uint256& y) noexcept
{
auto xp = uint128{x[2], x[3]};
auto yp = uint128{y[2], y[3]};
if (xp == yp)
{
xp = uint128{x[0], x[1]};
yp = uint128{y[0], y[1]};
}
return xp < yp;
}

[[gnu::noinline]] static bool lt_wordcmp(const uint256& x, const uint256& y) noexcept
{
for (size_t i = 3; i >= 1; --i)
Expand All @@ -370,6 +382,34 @@ BENCHMARK_TEMPLATE(shift, uint512, uint64_t, shl_public)->DenseRange(-1, 3);
return x[0] < y[0];
}

/// Find the first different word and compares it.
/// Proposed in https://github.com/chfast/intx/pull/269.
[[gnu::noinline]] static bool lt_ne(const uint256& x, const uint256& y) noexcept
{
for (auto i = uint256::num_words - 1; i > 0; --i)
{
if (x[i] != y[i])
return x[i] < y[i];
}
return x[0] < y[0];
}

/// A modification of lt_ne(). Smaller code, saves one cmp instruction.
[[gnu::noinline]] static bool lt_ne2(const uint256& x, const uint256& y) noexcept
{
auto a = x[3];
auto b = y[3];
for (auto i = uint256::num_words - 1; i > 0;)
{
if (a != b)
break;
--i;
a = x[i];
b = y[i];
}
return a < b;
}

[[gnu::noinline]] static bool lt_halves(const uint256& x, const uint256& y) noexcept
{
const auto xhi = uint128{x[2], x[3]};
Expand Down Expand Up @@ -426,7 +466,10 @@ static void compare(benchmark::State& state)
}
BENCHMARK_TEMPLATE(compare, lt_public)->DenseRange(0, 256, 64);
BENCHMARK_TEMPLATE(compare, lt_sub)->DenseRange(0, 256, 64);
BENCHMARK_TEMPLATE(compare, lt_split)->DenseRange(0, 256, 64);
BENCHMARK_TEMPLATE(compare, lt_wordcmp)->DenseRange(0, 256, 64);
BENCHMARK_TEMPLATE(compare, lt_ne)->DenseRange(0, 256, 64);
BENCHMARK_TEMPLATE(compare, lt_ne2)->DenseRange(0, 256, 64);
BENCHMARK_TEMPLATE(compare, lt_halves)->DenseRange(0, 256, 64);
#if INTX_HAS_EXTINT
BENCHMARK_TEMPLATE(compare, lt_llvm)->DenseRange(0, 256, 64);
Expand Down