diff options
Diffstat (limited to 'vendor/golang.org/x/text/internal/number/decimal.go')
| -rw-r--r-- | vendor/golang.org/x/text/internal/number/decimal.go | 46 |
1 files changed, 29 insertions, 17 deletions
diff --git a/vendor/golang.org/x/text/internal/number/decimal.go b/vendor/golang.org/x/text/internal/number/decimal.go index 62074e7d7..9b4035ec4 100644 --- a/vendor/golang.org/x/text/internal/number/decimal.go +++ b/vendor/golang.org/x/text/internal/number/decimal.go @@ -406,23 +406,35 @@ func (d *Decimal) ConvertFloat(r RoundingContext, x float64, size int) { // By default we get the exact decimal representation. verb := byte('g') prec := -1 - // Determine rounding, if possible. As the strconv API does not return the - // rounding accuracy (exact/rounded up|down), we can only round using - // ToNearestEven. - // Something like this would work: - // AppendDigits(dst []byte, x float64, base, size, prec int) (digits []byte, exp, accuracy int) - // - // TODO: At this point strconv's rounding is imprecise to the point that it - // is not useable for this purpose. - // See https://github.com/golang/go/issues/21714 - // if r.Mode == ToNearestEven { - // if n := r.RoundSignificantDigits(); n >= 0 { - // prec = n - // } else if n = r.RoundFractionDigits(); n >= 0 { - // prec = n - // verb = 'f' - // } - // } + // As the strconv API does not return the rounding accuracy, we can only + // round using ToNearestEven. + if r.Mode == ToNearestEven { + if n := r.RoundSignificantDigits(); n >= 0 { + prec = n + } else if n = r.RoundFractionDigits(); n >= 0 { + prec = n + verb = 'f' + } + } else { + // TODO: At this point strconv's rounding is imprecise to the point that + // it is not useable for this purpose. + // See https://github.com/golang/go/issues/21714 + // If rounding is requested, we ask for a large number of digits and + // round from there to simulate rounding only once. + // Ideally we would have strconv export an AppendDigits that would take + // a rounding mode and/or return an accuracy. Something like this would + // work: + // AppendDigits(dst []byte, x float64, base, size, prec int) (digits []byte, exp, accuracy int) + hasPrec := r.RoundSignificantDigits() >= 0 + hasScale := r.RoundFractionDigits() >= 0 + if hasPrec || hasScale { + // prec is the number of mantissa bits plus some extra for safety. + // We need at least the number of mantissa bits as decimals to + // accurately represent the floating point without rounding, as each + // bit requires one more decimal to represent: 0.5, 0.25, 0.125, ... + prec = 60 + } + } b := strconv.AppendFloat(d.Digits[:0], abs, verb, prec, size) i := 0 |