Skip to content

fix: keep the decimal point when rounding gains a digit #200

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
SashaMIT wants to merge 1 commit into
base: master
Choose a base branch
from
Open

fix: keep the decimal point when rounding gains a digit #200

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
15 changes: 7 additions & 8 deletions format.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -209,8 +209,11 @@ func (f *formatter) format(x *Big, format format, e byte) {
b = formatUnscaled(&x.unscaled)
}
orig := len(b)
b = roundString(b, x.Context.RoundingMode, !neg, f.prec)
exp = int(x.exp) + orig - len(b)
// A carry from 999 to 1000 adds a digit. That digit is a new leading
// place, so the scale stays tied to the requested precision.
req := f.prec
b = roundString(b, x.Context.RoundingMode, !neg, req)
exp = int(x.exp) + orig - req
} else if f.prec < 0 {
f.prec = -f.prec
exp = -f.prec
Expand Down Expand Up @@ -283,12 +286,8 @@ func (f *formatter) formatPlain(b []byte, exp int) {
default:
f.WriteString(zeroRadix)
io.CopyN(f, zeroReader{}, -int64(radix))

end := len(b)
if f.prec < end {
end = f.prec
}
f.Write(b[:end])
// Keep a carry digit. Dropping it shifts the value by a factor of ten.
f.Write(b)
}
}

Expand Down
16 changes: 16 additions & 0 deletions format_test.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -76,6 +76,22 @@ func TestDecimal_Format(t *testing.T) {
{"%.10f", "0.1234567891", "0.1234567891"},
{"%.10f", "0.01", "0.0100000000"},
{"%.10f", "0.0000000000000000000000000000000000000000000000000000000000001", "0.0000000000"},
// Rounding that gains a digit must not move the point one place left.
{"%.2f", "9.996208266660", "10.00"},
{"%.6f", "0.099999999999999999999999999999998", "0.100000"},
{"%.1f", "9.96", "10.0"},
{"%.0f", "9.96", "10"},
{"%.1f", "-9.96", "-10.0"},
{"%.0f", "999.5", "1000"},
{"%.3f", "0.09996", "0.100"},
{"%.3f", "0.9996", "1.000"},
{"%.1f", "99.96", "100.0"},
{"%.3f", "0.009996", "0.010"},
{"%.2e", "9.96", "1.00e+1"},
{"%.1f", "9.94", "9.9"},
{"%.1f", "1.25", "1.2"},
{"%.0f", "1.5", "2"},
{"%.0f", "2.5", "2"},
} {
z, _ := new(Big).SetString(s.input)
got := fmt.Sprintf(s.format, z)
Expand Down