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Fix rounding to zero error in stod on very small float numbers #10672

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merged 4 commits into from
Apr 23, 2022
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Merged

Fix rounding to zero error in stod on very small float numbers #10672

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f6f246c
Fix rounding error in stod on very small float numbers
davidwendt Apr 15, 2022
75db733
Merge branch 'branch-22.06' into stod-exp-min-check
davidwendt Apr 18, 2022
958f3f9
code for supporting subnormal float values from bdice
davidwendt Apr 18, 2022
a10e432
update comments
davidwendt Apr 18, 2022
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11 changes: 9 additions & 2 deletions cpp/src/strings/convert/convert_floats.cu
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Original file line number Diff line number Diff line change
Expand Up @@ -130,10 +130,17 @@ __device__ inline double stod(string_view const& d_str)
else if (exp_ten < std::numeric_limits<double>::min_exponent10)
return double{0};

double base = sign * static_cast<double>(digits);

exp_ten += 1 - num_digits;
// exp10() is faster than pow(10.0,exp_ten)
// extra floating-point division needed only in extreme range (e-287 - e-307)
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// where num_digits may push exp_ten below min_exponent10 (e-307)
if (exp_ten < std::numeric_limits<double>::min_exponent10) {
base = base / exp10(static_cast<double>(num_digits - 1));
exp_ten += num_digits - 1; // adjust exponent
}

double const exponent = exp10(static_cast<double>(std::abs(exp_ten)));
double const base = sign * static_cast<double>(digits);
return exp_ten < 0 ? base / exponent : base * exponent;
}

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4 changes: 3 additions & 1 deletion cpp/tests/strings/floats_tests.cpp
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Expand Up @@ -125,11 +125,13 @@ TEST_F(StringsConvertTest, FromFloats32)

TEST_F(StringsConvertTest, ToFloats64)
{
// clang-format off
std::vector<const char*> h_strings{
"1234", nullptr, "-876", "543.2", "-0.12", ".25",
"-.002", "", "-0.0", "1.28e256", "NaN", "abc123",
"123abc", "456e", "-1.78e+5", "-122.33644782", "12e+309", "1.7976931348623159E308",
"-Inf", "-INFINITY"};
"-Inf", "-INFINITY", "1.0", "1.7976931348623157e+308", "1.7976931348623157e-307"};
// clang-format on
cudf::test::strings_column_wrapper strings(
h_strings.begin(),
h_strings.end(),
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