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Fix handling of subnormals in exotic FP
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@ -216,7 +216,7 @@ template <typename F> struct basic_fp {
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template <typename Float> FMT_CONSTEXPR basic_fp(Float n) { assign(n); }
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// Assigns n to this and return true iff predecessor is closer than successor.
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template <typename Float> FMT_CONSTEXPR bool assign(Float n) {
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template <typename Float> FMT_CONSTEXPR auto assign(Float n) -> bool {
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static_assert((std::numeric_limits<Float>::is_iec559 &&
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std::numeric_limits<Float>::digits <= 113) ||
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is_float128<Float>::value,
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@ -250,7 +250,7 @@ using fp = basic_fp<unsigned long long>;
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template <int SHIFT = 0, typename F>
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FMT_CONSTEXPR basic_fp<F> normalize(basic_fp<F> value) {
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// Handle subnormals.
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const uint64_t implicit_bit = 1ULL << num_significand_bits<double>();
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const auto implicit_bit = F(1) << num_significand_bits<double>();
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const auto shifted_implicit_bit = implicit_bit << SHIFT;
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while ((value.f & shifted_implicit_bit) == 0) {
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value.f <<= 1;
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@ -2212,17 +2212,14 @@ FMT_HEADER_ONLY_CONSTEXPR20 int format_float(Float value, int precision,
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unsigned dragon_flags = 0;
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if (!is_fast_float<Float>()) {
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const auto inv_log2_10 = 0.3010299956639812; // 1 / log2(10)
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const auto e = basic_fp<typename dragonbox::float_info<
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decltype(converted_value)>::carrier_uint>(converted_value)
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.e;
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using info = dragonbox::float_info<decltype(converted_value)>;
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const auto f = basic_fp<typename info::carrier_uint>(converted_value);
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// Compute exp, an approximate power of 10, such that
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// 10^(exp - 1) <= value < 10^exp or 10^exp <= value < 10^(exp + 1).
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// This is based on log10(value) == log2(value) / log2(10) and approximation
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// of log2(value) by e + num_fraction_bits idea from double-conversion.
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auto num_fraction_bits =
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num_significand_bits<Float>() - (has_implicit_bit<Float>() ? 0 : 1);
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exp = static_cast<int>(
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std::ceil((e + num_fraction_bits) * inv_log2_10 - 1e-10));
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std::ceil((f.e + count_digits<1>(f.f) - 1) * inv_log2_10 - 1e-10));
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dragon_flags = dragon::fixup;
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} else if (!is_constant_evaluated() && precision < 0) {
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// Use Dragonbox for the shortest format.
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@ -1009,6 +1009,8 @@ TEST(format_test, precision) {
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if (std::numeric_limits<long double>::digits == 64) {
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auto ld = (std::numeric_limits<long double>::min)();
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EXPECT_EQ(fmt::format("{:.0}", ld), "3e-4932");
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EXPECT_EQ(fmt::format("{:0g}", 5.02957084971264961283E-4940L),
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"5.02957e-4940");
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}
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EXPECT_EQ("123.", fmt::format("{:#.0f}", 123.0));
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