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fix: round negative fractions toward zero #490

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fix: round negative fractions toward zero #490

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4 changes: 4 additions & 0 deletions numeric.go
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Original file line number Diff line number Diff line change
Expand Up @@ -115,9 +115,13 @@ func round(a interface{}, p int, rOpt ...float64) float64 {
var round float64
pow := math.Pow(10, places)
digit := pow * val
// Modf keeps the sign of the fraction. A negative fraction below the
// threshold rounds toward zero, matching the positive side.
_, div := math.Modf(digit)
if div >= roundOn {
round = math.Ceil(digit)
} else if div < 0 && div > -roundOn {
round = math.Ceil(digit)
} else {
round = math.Floor(digit)
}
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9 changes: 9 additions & 0 deletions numeric_test.go
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Expand Up @@ -298,6 +298,15 @@ func TestRound(t *testing.T) {
assert.Equal(t, 123.0, round(123.49999999, 0))
assert.Equal(t, 123.23, round(123.2329999, 2, .3))
assert.Equal(t, 123.24, round(123.233, 2, .3))
// A negative fraction below the threshold rounds toward zero.
// -1.25 is exact in float64. Floor would return -2.
assert.Equal(t, -1.0, round(-1.25, 0))
assert.Equal(t, -2.0, round(-1.5, 0))
assert.Equal(t, -2.0, round(-1.75, 0))
assert.Equal(t, -123.0, round(-123.49999999, 0))
assert.Equal(t, -124.0, round(-123.500001, 0))
assert.Equal(t, -123.23, round(-123.2329999, 2, .3))
assert.Equal(t, -123.24, round(-123.233, 2, .3))
}

func TestRandomInt(t *testing.T) {
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