Inconsistent (or buggy) Quantize behavior

[LasTshaMAN]

Looks like Quantize(result, amount, 0) func works differently for:

• when amount is of the form N.0* (where N is integer number and N != 0)
• when amount is of the form 0.0*

Here is a simple test to reproduce this (with v3.1.0):

// quantize is a simple wrapper around `apd` library.
func quantize(amount *apd.Decimal, decimalPlaces uint32, roundingRule apd.Rounder) (*apd.Decimal, error) {
	ctx := apd.BaseContext.WithPrecision(infinitePrecision)
	ctx.Rounding = roundingRule

	var amt apd.Decimal
	exp := -int32(decimalPlaces)
	_, err := ctx.Quantize(&amt, amount, exp)

	return &amt, err
}

func TestQuantizeRounding(t *testing.T) {
        // 1.1 -> 2 (works as expected)
	got, err = quantize(apd.New(11, -1), 0, apd.RoundUp)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	want = apd.New(2, 0)
	if want.CmpTotal(got) != 0 {
		t.Fatalf("want: %+v, got: %+v", want, got)
	}

        // 1.01 -> 2 (works as expected)
	got, err := quantize(apd.New(101, -2), 0, apd.RoundUp)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	want := apd.New(2, 0)
	if want.CmpTotal(got) != 0 {
		t.Fatalf("want: %+v, got: %+v", want, got)
	}

        // 0.1 -> 1 (works as expected)
	got, err = quantize(apd.New(1, -1), 0, apd.RoundUp)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	want = apd.New(1, 0)
	if want.CmpTotal(got) != 0 {
		t.Fatalf("want: %+v, got: %+v", want, got)
	}

        // 0.01 -> 1 (doesn't work as expected! instead it does 0.01 -> 0 for some reason)
	got, err = quantize(apd.New(1, -2), 0, apd.RoundUp)
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	want = apd.New(1, 0)
	if want.CmpTotal(got) != 0 {
		t.Fatalf("want: %+v, got: %+v", want, got)
	}
}

[LasTshaMAN]

Can observe similar discrepancy for negative values:

                 // -0.01 -> -1 (doesn't work as expected! instead it does -0.01 -> 0 for some reason)
		got, err = quantize(apd.New(-1, -2), 0, apd.RoundUp)
		if err != nil {
			t.Fatalf("unexpected error: %v", err)
		}
		want = apd.New(-1, 0)
		if want.CmpTotal(got) != 0 {
			t.Fatalf("want: %+v, got: %+v", want, got)
		}

[LasTshaMAN]

And exp param (decimalPlaces in my notation above) doesn't have to be 0, I was also able to reproduce this with -1 (or decimalPlaces being 1 is the equivalent) for example.