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Improve accuracy of Number::operator+=

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- Use more of the available range of the uint128 operands.
- Also refactor Number::Guard::round() to return an enum.
This commit is contained in:
Ed Hennis
2026-06-02 15:35:42 -04:00
parent 35bee87909
commit 9e8c3caef4
2 changed files with 67 additions and 46 deletions
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75
src/test/basics/Number_test.cpp
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@@ -179,33 +179,34 @@ public:
testcase << "test_add " << to_string(scale);
using Case = std::tuple<Number, Number, Number, int>;
auto const cSmall = std::to_array<Case>(
{{Number{1'000'000'000'000'000, -15},
Number{6'555'555'555'555'555, -29},
Number{1'000'000'000'000'066, -15},
__LINE__},
{Number{-1'000'000'000'000'000, -15},
Number{-6'555'555'555'555'555, -29},
Number{-1'000'000'000'000'066, -15},
__LINE__},
{Number{-1'000'000'000'000'000, -15},
Number{6'555'555'555'555'555, -29},
Number{-9'999'999'999'999'344, -16},
__LINE__},
{Number{-6'555'555'555'555'555, -29},
Number{1'000'000'000'000'000, -15},
Number{9'999'999'999'999'344, -16},
__LINE__},
{Number{}, Number{5}, Number{5}, __LINE__},
{Number{5}, Number{}, Number{5}, __LINE__},
{Number{5'555'555'555'555'555, -32768},
Number{-5'555'555'555'555'554, -32768},
Number{0},
__LINE__},
{Number{-9'999'999'999'999'999, -31},
Number{1'000'000'000'000'000, -15},
Number{9'999'999'999'999'990, -16},
__LINE__}});
auto const cSmall = std::to_array<Case>({
{Number{1'000'000'000'000'000, -15},
Number{6'555'555'555'555'555, -29},
Number{1'000'000'000'000'066, -15},
__LINE__},
{Number{-1'000'000'000'000'000, -15},
Number{-6'555'555'555'555'555, -29},
Number{-1'000'000'000'000'066, -15},
__LINE__},
{Number{-1'000'000'000'000'000, -15},
Number{6'555'555'555'555'555, -29},
Number{-9'999'999'999'999'344, -16},
__LINE__},
{Number{-6'555'555'555'555'555, -29},
Number{1'000'000'000'000'000, -15},
Number{9'999'999'999'999'344, -16},
__LINE__},
{Number{}, Number{5}, Number{5}, __LINE__},
{Number{5}, Number{}, Number{5}, __LINE__},
{Number{5'555'555'555'555'555, -32768},
Number{-5'555'555'555'555'554, -32768},
Number{0},
__LINE__},
{Number{-9'999'999'999'999'999, -31},
Number{1'000'000'000'000'000, -15},
Number{9'999'999'999'999'990, -16},
__LINE__},
});
auto const cLarge = std::to_array<Case>(
// Note that items with extremely large mantissas need to be
// calculated, because otherwise they overflow uint64. Items from C
@@ -2021,13 +2022,27 @@ public:
BigInt const exact = toBigInt(a) + toBigInt(b);
BigInt const stored = toBigInt(sum);
BigInt const diff = stored - exact;
log << "\n exact a + b = " << exact.str() << "\n TowardsZero = " << stored.str()
<< "\n";
log << "\n a = " << a << "\n b = " << b
<< "\n exact a + b = " << exact.str() << "\n TowardsZero = " << stored.str()
<< "\n difference = " << diff.str() << "\n";
log.flush();
if (scale != MantissaRange::MantissaScale::LargeLegacy)
if (scale == MantissaRange::MantissaScale::Small)
{
BEAST_EXPECT(stored == exact);
}
else if (scale == MantissaRange::MantissaScale::LargeLegacy)
{
BEAST_EXPECT(stored > exact);
}
else
{
BEAST_EXPECT(stored < exact);
BEAST_EXPECT(diff < 0);
BEAST_EXPECT(-diff < pow10<BigInt>(sum.exponent()));
}
}
}