The ptolemy.math.FixedPoint class does not seem to handle bit growth
properly for add or subtract operations. For multiplies, the fixed point
format grows automatically as part of the operation. However, no bit
growth is provided for add or subtract. I would suggest that add and
subtract increase the "inBits" of the new FixPoint value when the
intBits field of both operands are the same. This will allow the fixed
point value to grow when an "overflow" occurs during addition and
subtraction.
Original code (for add):
public FixPoint add(FixPoint arg) {
int fracBits = Math.max(_frac_bits, arg._frac_bits);
int intBits = Math.max(_int_bits, arg._int_bits);
BigInteger thisValue = _alignToFraction(fracBits);
BigInteger thatValue = arg._alignToFraction(fracBits);
return new FixPoint(thisValue.add(thatValue), intBits, fracBits);
}
Suggested code:
public FixPoint add(FixPoint arg) {
int fracBits = Math.max(_frac_bits, arg._frac_bits);
int intBits = Math.max(_int_bits, arg._int_bits);
if (_int_bits == arg._int_Bits)
intBits++;
BigInteger thisValue = _alignToFraction(fracBits);
BigInteger thatValue = arg._alignToFraction(fracBits);
return new FixPoint(thisValue.add(thatValue), intBits, fracBits);
}
--
Michael J. Wirthlin
Associate Professor
Electrical and Computer Engineering Voice: (801) 422-7601
Brigham Young University Fax: (801) 422-0201
459 Clyde Building Email: [EMAIL PROTECTED]
Provo, UT 84602 www.ee.byu.edu/faculty/wirthlin
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