hcrosse commented on code in PR #1515:
URL: https://github.com/apache/arrow-go/pull/1515#discussion_r4530764149
##########
arrow/decimal128/decimal128.go:
##########
@@ -282,14 +283,35 @@ func FromString(v string, prec, scale int32) (n Num, err
error) {
return Num{}, errors.New("bitlen too large for
decimal128")
}
n = FromBigInt(val)
- n, _ = n.Div(scaleMultipliers[-scale])
+ if scale >= -MaxScale {
+ n, _ = n.Div(scaleMultipliers[-scale])
+ } else {
+ // |n| < 2^127 < 10^39, so the quotient is zero.
+ n = Num{}
+ }
} else {
// Since we're going to truncate this to get an integer, we
need to round
// the value instead because of edge cases so that we match how
other implementations
// (e.g. C++) handles Decimal values. So if we're negative
we'll subtract 0.5 and if
// we're positive we'll add 0.5.
- p := (&big.Float{}).SetInt(scaleMultipliers[scale].BigInt())
- out.SetPrec(precInBits).Mul(out, p)
+ if scale <= MaxScale {
+ p :=
(&big.Float{}).SetInt(scaleMultipliers[scale].BigInt())
+ out.SetPrec(precInBits).Mul(out, p)
+ } else {
+ pow10.Mul(out.SetPrec(precInBits), int64(scale), 128+64)
Review Comment:
This is existing behavior, not something the path past the table adds.
`FromString` parses into a `big.Float` before scaling, so an exact decimal tie
can land just below one half at any scale. Main already returns 3 for
`decimal128.FromString("0.35", 38, 1)`. Resolving ties from the decimal text
would change results inside the tables for all four widths, so it is out of
scope for this PR.
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