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Update some comments, and const correctness

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This commit is contained in:
Ed Hennis
2026-06-18 20:59:20 -04:00
parent 4124a1dd2d
commit 7cb224e50f
2 changed files with 30 additions and 26 deletions
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46
src/libxrpl/basics/Number.cpp
View File

@@ -295,11 +295,11 @@ public:
// Modify the result to the correctly rounded value
template <UnsignedMantissa T>
void
doRoundDown(bool& negative, T& mantissa, int& exponent);
doRoundDown(bool& negative, T& mantissa, int& exponent) const;
// Modify the result to the correctly rounded value
void
doRound(rep& drops, std::string location);
doRound(rep& drops, std::string location) const;
private:
template <UnsignedMantissa T>
@@ -333,7 +333,7 @@ private:
template <UnsignedMantissa T>
void
bringIntoRange(bool& negative, T& mantissa, int& exponent);
bringIntoRange(bool& negative, T& mantissa, int& exponent) const;
};
inline void
@@ -425,15 +425,13 @@ Number::Guard::pushOverflow(T mantissa)
// Round in two steps.
// The first step uses the digits _already_ in the Guard to round the
// intermediate mantissa, using only the last digit. Then update the mantissa for the
// second step. Ultimately, the purpose of this step is to capture rounding where the stored
// digits would change the decision without those digits. (e.g. From just _below_ the
// midpoint to just _above_ the midpoint for ToNearest, or from kMaxRep into the in-between
// for Upward.
// Make an exception if the final digit is 9, because it can only get larger, and we want to
// stay in single digits.
if (auto finalDigit = mantissa % 10; finalDigit < 9)
// The first step uses the digits _already_ in the Guard to possibly round the mantissa up.
// Ultimately, the purpose of this step is to capture rounding where the stored digits would
// change the decision without those digits. (e.g. From just _below_ the midpoint to just
// _above_ the midpoint for ToNearest, or from kMaxRep into the in-between for Upward. Make
// an exception if the final digit is 9, because it can only get larger, and we don't want
// to bump up to kMaxRepUp.
if (mantissa % 10 < 9)
{
// Intentionally use integer math to get the largest value under the midpoint.
auto constexpr kMidpoint = kMaxRep + (spread / 2);
@@ -447,15 +445,15 @@ Number::Guard::pushOverflow(T mantissa)
if (mantissa == kMaxRep)
{
// If the mantissa ends up exactly kMaxRep, there's nothing more to do.
// If the mantissa ends up exactly kMaxRep, there's nothing more to do here.
return;
}
// The second step scales the final digit of the update mantissa proportionally from kMaxRep
// and kMaxRepUp to 1 to 9. It then pushes that scaled digit onto the guard as if it was a
// digit that got removed, but don't actually remove it. This method should be is
// The second step scales the final digit of the update mantissa proportionally, converting
// from (kMaxRep, kMaxRepUp) to (0 to 9]. It then pushes that scaled digit onto the guard as
// if it was a digit that got removed, but doesn't actually remove it. This method should be
// future-proof in case the number of mantissa bits ever changes. (Though for integer values
// that are a power of two themselves, the spread will always be the same.) Effects:
// of the form 2^(2^x-1), the spread will always be the same.) Effects:
// * For round to nearest
// * if the updated mantissa is below the midpoint, it'll round "down" to kMaxRep
// * if above the midpoint, it'll round "up" to kMaxRepUp
@@ -527,7 +525,7 @@ Number::Guard::round() const noexcept
template <UnsignedMantissa T>
void
Number::Guard::bringIntoRange(bool& negative, T& mantissa, int& exponent)
Number::Guard::bringIntoRange(bool& negative, T& mantissa, int& exponent) const
{
// Bring mantissa back into the minMantissa / maxMantissa range AFTER
// rounding. Mantissa should never be 0.
@@ -575,7 +573,9 @@ Number::Guard::doRoundUp(bool& negative, T& mantissa, int& exponent, std::string
if (cuspRoundingFix >= MantissaRange::CuspRoundingFix::Enabled330 &&
mantissa > kMaxRep && mantissa < kMaxRepUp)
{
//
// When rounding up a value in between kMaxRep, and kMaxRepUp, round to
// kMaxRepUp. Note that the decision for this rounding is dominated by the
// results of pushOverflow.
mantissa = kMaxRepUp;
}
else
@@ -614,6 +614,8 @@ Number::Guard::doRoundUp(bool& negative, T& mantissa, int& exponent, std::string
cuspRoundingFix >= MantissaRange::CuspRoundingFix::Enabled330 && mantissa > kMaxRep &&
mantissa < kMaxRepUp)
{
// When rounding down a value in between kMaxRep, and kMaxRepUp, round to kMaxRep.
// Note that the decision for this rounding is dominated by the results of pushOverflow.
mantissa = kMaxRep;
}
bringIntoRange(negative, mantissa, exponent);
@@ -623,7 +625,7 @@ Number::Guard::doRoundUp(bool& negative, T& mantissa, int& exponent, std::string
template <UnsignedMantissa T>
void
Number::Guard::doRoundDown(bool& negative, T& mantissa, int& exponent)
Number::Guard::doRoundDown(bool& negative, T& mantissa, int& exponent) const
{
// Do not pushOverflow here.
@@ -659,8 +661,10 @@ Number::Guard::doRoundDown(bool& negative, T& mantissa, int& exponent)
// Modify the result to the correctly rounded value
void
Number::Guard::doRound(rep& drops, std::string location)
Number::Guard::doRound(rep& drops, std::string location) const
{
// Do not pushOverflow here.
auto r = round();
if (r == Round::Up || (r == Round::Even && (drops & 1) == 1))
{

10
src/test/basics/Number_test.cpp
View File

@@ -2574,7 +2574,7 @@ public:
Number const below{static_cast<std::int64_t>(Number::kMaxRep), 0};
Number const above{false, Number::kMaxRepUp, 0, Number::Normalized{}};
log << "Below: " << below << ", Above: " << above << std::endl;
log << "Below: " << below << ", Above: " << above << "\n";
auto const zeroPointFour = Number(4, -1);
auto const zeroPointSix = Number(6, -1);
@@ -2663,9 +2663,9 @@ public:
ss << "kMaxRep + " << operand << " rounded " << to_string(mode) << " to " << actual
<< ". Expected: " << expectedValue;
if (BEAST_EXPECTS(actual == expectedValue, ss.str()))
log << "\tSUCCESS: " << to_string(scale) << " " << ss.str() << std::endl;
log << "\tSUCCESS: " << to_string(scale) << " " << ss.str() << "\n";
}
log << std::endl;
log << "\n";
}
// Subtraction cases test kMaxRepUp - Operand
@@ -2720,9 +2720,9 @@ public:
ss << "kMaxRepUp - " << operand << " rounded " << to_string(mode) << " to "
<< actual << ". Expected: " << expectedValue;
if (BEAST_EXPECTS(actual == expectedValue, ss.str()))
log << "\tSUCCESS: " << to_string(scale) << " " << ss.str() << std::endl;
log << "\tSUCCESS: " << to_string(scale) << " " << ss.str() << "\n";
}
log << std::endl;
log << "\n";
}
}