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Fix numeric to float64 conversion #212

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merged 3 commits into from
Feb 6, 2024
Merged

Fix numeric to float64 conversion #212

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77b8b32
Fix numeric to float64 conversion
jschaf Feb 1, 2024
91d2ae3
Remove special case for exp == 1
jschaf Feb 5, 2024
8a32252
Rename test case
jschaf Feb 5, 2024
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5 changes: 4 additions & 1 deletion numeric.go
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Original file line number Diff line number Diff line change
Expand Up @@ -448,8 +448,11 @@ func (src *Numeric) toFloat64() (float64, error) {
return math.Inf(-1), nil
}

if src.Exp == 1 {
switch {
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This optimization isn't present in pgx@v5 so I don't think there's anything to fix in v5.

https://github.com/jackc/pgx/blob/20bf953a17fc7cf6619536a87bd285b9273dbcf9/pgtype/numeric.go#L66

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Please double-check my logic. I think src.Int is normalized, so this optimization is valid.

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I think there is a danger of integer overflow in float64(src.Int.Int64() * 10). I think it should be float64(src.Int.Int64()) * 10 instead. But more so, is that branch even necessary / valuable. I assume it would work without it.

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@jschaf jschaf Feb 5, 2024 •
edited
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I removed the case for exp == 1 since you're right; it's not necessary. I originally kept that case since I thought it was important for the original optimization.

If you wanted to get fancy, you could implement it for all positive exponents, but I'll leave just the case for exp == 0 for now.

	if src.Exp >= 0 {
		return float64(src.Int.Int64()) * math.Pow10(int(src.Exp)), nil
	}

case src.Exp == 0:
return float64(src.Int.Int64()), nil
case src.Exp == 1:
return float64(src.Int.Int64() * 10), nil
}

buf := make([]byte, 0, 32)
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20 changes: 20 additions & 0 deletions numeric_test.go
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Expand Up @@ -385,6 +385,7 @@ func TestNumericEncodeDecodeBinary(t *testing.T) {
123,
0.000012345,
1.00002345,
50.000000,
math.NaN(),
float32(math.NaN()),
math.Inf(1),
Expand Down Expand Up @@ -442,3 +443,22 @@ func TestNumericSmallNegativeValues(t *testing.T) {
t.Fatalf("expected %s, got %s", "-0.000123", s)
}
}

// https://github.com/jackc/pgtype/issues/210
func TestNumericFloat64(t *testing.T) {
n := pgtype.Numeric{
Int: big.NewInt(5),
Exp: 1,
Status: pgtype.Present,
}

var f float64
err := n.AssignTo(&f)
if err != nil {
t.Fatal(err)
}

if f != 50.0 {
t.Fatalf("expected %s, got %f", "50", f)
}
}
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