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Avoid double counting digits in normalization process #1125

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Merged
mborland merged 1 commit into from
Oct 13, 2025
Merged

Avoid double counting digits in normalization process #1125

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2 changes: 1 addition & 1 deletion include/boost/decimal/decimal128_t.hpp
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Expand Up @@ -728,7 +728,7 @@ constexpr decimal128_t::decimal128_t(T1 coeff, T2 exp, bool sign) noexcept
{
if (coeff > detail::d128_max_significand_value || biased_exp < 0)
{
coeff_digits = detail::coefficient_rounding<decimal128_t>(coeff, exp, biased_exp, sign);
coeff_digits = detail::coefficient_rounding<decimal128_t>(coeff, exp, biased_exp, sign, detail::num_digits(coeff));
}
}

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2 changes: 1 addition & 1 deletion include/boost/decimal/decimal32_t.hpp
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Expand Up @@ -635,7 +635,7 @@ constexpr decimal32_t::decimal32_t(T1 coeff, T2 exp, bool sign) noexcept // NOLI
auto biased_exp {static_cast<int>(exp + detail::bias)};
if (coeff > detail::d32_max_significand_value || biased_exp < 0)
{
coeff_digits = detail::coefficient_rounding<decimal32_t>(coeff, exp, biased_exp, sign);
coeff_digits = detail::coefficient_rounding<decimal32_t>(coeff, exp, biased_exp, sign, detail::num_digits(coeff));
}

auto reduced_coeff {static_cast<significand_type>(coeff)};
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2 changes: 1 addition & 1 deletion include/boost/decimal/decimal64_t.hpp
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Expand Up @@ -629,7 +629,7 @@ constexpr decimal64_t::decimal64_t(T1 coeff, T2 exp, bool sign) noexcept
auto biased_exp {static_cast<int>(exp) + detail::bias_v<decimal64_t>};
if (coeff > detail::d64_max_significand_value || biased_exp < 0)
{
coeff_digits = detail::coefficient_rounding<decimal64_t>(coeff, exp, biased_exp, sign);
coeff_digits = detail::coefficient_rounding<decimal64_t>(coeff, exp, biased_exp, sign, detail::num_digits(coeff));
}

auto reduced_coeff {static_cast<significand_type>(coeff)};
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4 changes: 1 addition & 3 deletions include/boost/decimal/detail/fenv_rounding.hpp
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Expand Up @@ -182,14 +182,12 @@ constexpr auto fenv_round(T& val, bool is_neg = false, bool sticky = false) noex
#endif

template <typename TargetDecimalType, typename T1, typename T2, typename T3>
constexpr auto coefficient_rounding(T1& coeff, T2& exp, T3& biased_exp, const bool sign) noexcept
constexpr auto coefficient_rounding(T1& coeff, T2& exp, T3& biased_exp, const bool sign, int coeff_digits) noexcept
{
// T1 will be a 128-bit or 256-bit
using sig_type = typename TargetDecimalType::significand_type;
using demoted_integer_type = std::conditional_t<std::numeric_limits<T1>::digits10 < std::numeric_limits<sig_type>::digits10, T1, sig_type>;

auto coeff_digits {detail::num_digits(coeff)};

// How many digits need to be shifted?
const auto shift_for_large_coeff {(coeff_digits - detail::precision_v<TargetDecimalType>) - 1};
int shift {};
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2 changes: 1 addition & 1 deletion include/boost/decimal/detail/normalize.hpp
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Expand Up @@ -31,7 +31,7 @@ constexpr auto normalize(T1& significand, T2& exp, bool sign = false) noexcept -
else if (digits > target_precision)
{
auto biased_exp {static_cast<int>(exp) + detail::bias_v<TargetDecimalType>};
detail::coefficient_rounding<TargetDecimalType>(significand, exp, biased_exp, sign);
detail::coefficient_rounding<TargetDecimalType>(significand, exp, biased_exp, sign, digits);
}
}

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