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avoid precision loss warning in magnitudes' root; fixes #611

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This commit is contained in:
Yves Delley
2024-09-14 21:37:00 +02:00
parent ae816a97fc
commit 9ca56f6911
1 changed files with 6 additions and 5 deletions
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11
src/core/include/mp-units/framework/magnitude.h
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@@ -380,8 +380,9 @@ template<typename T>
// Always use `long double` for intermediate computations. We don't ever expect people to be
// calling this at runtime, so we want maximum accuracy.
long double xld = static_cast<long double>(x);
long double lo = 1.0;
long double hi = static_cast<long double>(x);
long double hi = xld;
// Do a binary search to find the closest value such that `checked_int_pow` recovers the input.
//
@@ -398,7 +399,7 @@ template<typename T>
}
// Early return if we get lucky with an exact answer.
if (result.value() == x) {
if (result.value() == xld) {
return static_cast<T>(mid);
}
@@ -408,7 +409,7 @@ template<typename T>
}
// Preserve the invariant that `checked_int_pow(lo, n) < x < checked_int_pow(hi, n)`.
if (result.value() < x) {
if (result.value() < xld) {
lo = mid;
} else {
hi = mid;
@@ -416,8 +417,8 @@ template<typename T>
}
// Pick whichever one gets closer to the target.
const auto lo_diff = x - checked_int_pow(lo, n).value();
const auto hi_diff = checked_int_pow(hi, n).value() - x;
const auto lo_diff = xld - checked_int_pow(lo, n).value();
const auto hi_diff = checked_int_pow(hi, n).value() - xld;
return static_cast<T>(lo_diff < hi_diff ? lo : hi);
}