diff options
Diffstat (limited to 'lib/Support/APFloat.cpp')
-rw-r--r-- | lib/Support/APFloat.cpp | 13 |
1 files changed, 8 insertions, 5 deletions
diff --git a/lib/Support/APFloat.cpp b/lib/Support/APFloat.cpp index 34bc6b6..676e2d4 100644 --- a/lib/Support/APFloat.cpp +++ b/lib/Support/APFloat.cpp @@ -3546,11 +3546,14 @@ void APFloat::toString(SmallVectorImpl<char> &Str, // Set FormatPrecision if zero. We want to do this before we // truncate trailing zeros, as those are part of the precision. if (!FormatPrecision) { - // It's an interesting question whether to use the nominal - // precision or the active precision here for denormals. - - // FormatPrecision = ceil(significandBits / lg_2(10)) - FormatPrecision = (semantics->precision * 59 + 195) / 196; + // We use enough digits so the number can be round-tripped back to an + // APFloat. The formula comes from "How to Print Floating-Point Numbers + // Accurately" by Steele and White. + // FIXME: Using a formula based purely on the precision is conservative; + // we can print fewer digits depending on the actual value being printed. + + // FormatPrecision = 2 + floor(significandBits / lg_2(10)) + FormatPrecision = 2 + semantics->precision * 59 / 196; } // Ignore trailing binary zeros. |