// Parse an IEEE-754 decimal format to a FbDecFloat.
public FbDecFloat ParseBytes(byte[] decBytes)
{
// this (and related) code works with BE
if (BitConverter.IsLittleEndian)
{
Array.Reverse(decBytes);
}
_decimalFormat.ValidateByteLength(decBytes);
var firstByte = decBytes[0] & 0xff;
var signum = -1 * UnsignedRightShift(firstByte, 7) | 1;
var decimalType = DecimalTypeFromFirstByte(firstByte);
switch (decimalType)
{
case DecimalType.Infinity:
return(signum == NegativeSignum ? FbDecFloat.NegativeInfinity : FbDecFloat.PositiveInfinity);
case DecimalType.NaN:
return(signum == NegativeSignum ? FbDecFloat.NegativeNaN : FbDecFloat.PositiveNaN);
case DecimalType.SignalingNaN:
return(signum == NegativeSignum ? FbDecFloat.NegativeSignalingNaN : FbDecFloat.PositiveSignalingNaN);
case DecimalType.Finite:
{
// NOTE: get exponent MSB from combination field and first 2 bits of exponent continuation in one go
int exponentMSB;
int firstDigit;
if ((firstByte & Combination2) != Combination2)
{
exponentMSB = UnsignedRightShift(firstByte, 3) & 0b01100 | (firstByte & 0b011);
firstDigit = UnsignedRightShift(firstByte, 2) & 0b0111;
}
else
{
exponentMSB = UnsignedRightShift(firstByte, 1) & 0b01100 | (firstByte & 0b011);
firstDigit = 0b01000 | (UnsignedRightShift(firstByte, 2) & 0b01);
}
var exponentBitsRemaining = _decimalFormat.ExponentContinuationBits - 2;
Debug.Assert(exponentBitsRemaining == _decimalFormat.FormatBitLength - 8 - _decimalFormat.CoefficientContinuationBits, $"Unexpected exponent remaining length {exponentBitsRemaining}.");
var exponent = _decimalFormat.UnbiasedExponent(DecodeExponent(decBytes, exponentMSB, exponentBitsRemaining));
var coefficient = _coefficientCoder.DecodeValue(signum, firstDigit, decBytes);
return(new FbDecFloat(DecimalType.Finite, signum == NegativeSignum, coefficient, exponent));
}
default:
throw new ArgumentOutOfRangeException();
}
}