Function EncodeNonsortingDecimal

postgres/parser/encoding/decimal.go:543–608

EncodeNonsortingDecimal returns the resulting byte slice with the encoded decimal appended to b. The encoding is limited compared to standard encodings in this package in that - It will not sort lexicographically - It does not encode its length or terminate itself, so decoding functions must be prov

(b []byte, d *apd.Decimal)

//	decimalInfinity         -> decimalInfinity
//	decimalNaNDesc          -> decimalNaNDesc
func EncodeNonsortingDecimal(b []byte, d *apd.Decimal) []byte {
	neg := d.Negative
	switch d.Form {
	case apd.Finite:
		// ignore
	case apd.Infinite:
		if neg {
			return append(b, decimalNegativeInfinity)
		}
		return append(b, decimalInfinity)
	case apd.NaN:
		return append(b, decimalNaN)
	default:
		panic(errors.Errorf("unknown form: %s", d.Form))
	}

	// We only encode "0" as decimalZero. All others ("0.0", "-0", etc) are
	// encoded like normal values.
	if d.IsZero() && !neg && d.Exponent == 0 {
		return append(b, decimalZero)
	}

	// Determine the exponent of the decimal, with the
	// exponent defined as .xyz * 10^exp.
	nDigits := int(d.NumDigits())
	e := nDigits + int(d.Exponent)

	bNat := d.Coeff.Bits()

	var buf []byte
	if n := UpperBoundNonsortingDecimalSize(d); n <= cap(b)-len(b) {
		// We append the marker directly to the input buffer b below, so
		// we are off by 1 for each of these, which explains the adjustments.
		buf = b[len(b)+1 : len(b)+1]
	} else {
		buf = make([]byte, 0, n-1)
	}

	switch {
	case neg && e > 0:
		b = append(b, decimalNegLarge)
		buf = encodeNonsortingDecimalValue(uint64(e), bNat, buf)
		return append(b, buf...)
	case neg && e == 0:
		b = append(b, decimalNegMedium)
		buf = encodeNonsortingDecimalValueWithoutExp(bNat, buf)
		return append(b, buf...)
	case neg && e < 0:
		b = append(b, decimalNegSmall)
		buf = encodeNonsortingDecimalValue(uint64(-e), bNat, buf)
		return append(b, buf...)
	case !neg && e < 0:
		b = append(b, decimalPosSmall)
		buf = encodeNonsortingDecimalValue(uint64(-e), bNat, buf)
		return append(b, buf...)
	case !neg && e == 0:
		b = append(b, decimalPosMedium)
		buf = encodeNonsortingDecimalValueWithoutExp(bNat, buf)