fixedint.py enhanced for auto-coercion (fixed-width python integers)

[Andy Sy]

Hi Dan,

I find that when doing bit-twiddling in pure Python,
fixed-width integer support is an extremely handy
capability to have in Python regardless of what
the apologists (for its absence) say.


I added some stuff to fixedint.py to make
fixedint.SignedType(8)(24)

the above work. Perhaps you can review the
code to see if there are any major flaws in it?


Right after I started using it, I realized
there has to be a lot more thought put into
the conventions for the coecion rules. What
should

return for example... ?





----- START OF CODE -----


import operator

def _toFixedUnsigned(n, b):
"Truncate n to a b-bit unsigned long."
return n & ((1L << b) - 1) # bitmask of b 1's

def _toFixedSigned(n, b):
"Truncate n to a b-bit signed long."
result = _toFixedUnsigned(n, b)
if result >= (1L << b - 1): # More than "maxint"?
result -= 1L << b # Then wrap around.
return result

class _Integer(object):
"Abstract base class for SignedType and UnsignedType."
# Numeric conversions
def __long__(self):
return self._value
def __int__(self):
return int(self._value)
def __float__(self):
return float(self._value)
def __nonzero__(self):
return self._value != 0
# String conversions.
def __str__(self):
return str(self._value)
# Arithmetic
def __pos__(self):
return self
def __neg__(self):
return type(self)(-self._value)
def __add__(self, other):
if isinstance(other, type(self)):
return type(self)(self._value + other._value)
else:
return type(self)(self._value + self.__class__(other)._value)
def __sub__(self, other):
if isinstance(other, type(self)):
return type(self)(self._value - other._value)
else:
return type(self)(self._value - self.__class__(other)._value)
def __mul__(self, other):
if isinstance(other, type(self)):
return type(self)(self._value * other._value)
else:
return type(self)(self._value * self.__class__(other)._value)
def __floordiv__(self, other):
if isinstance(other, type(self)):
return type(self)(self._value // other._value)
else:
return type(self)(self._value // self.__class__(other)._value)
def __mod__(self, other):
if isinstance(other, type(self)):
return type(self)(self._value % other._value)
else:
return type(self)(self._value % self.__class__(other)._value)
def __divmod__(self, other):
return self // other, self % other
# Relational
def __cmp__(self, other):
return cmp(long(self), other)
# Bit-bashing
def __lshift__(self, other):
return type(self)(self._value << other)
def __rshift__(self, other):
return type(self)(self._value >> other)
def __invert__(self):
return type(self)(~self._value)
def __and__(self, other):
if isinstance(other, type(self)):
return type(self)(self._value & other._value)
else:
return type(self)(self._value & self.__class__(other)._value)
def __or__(self, other):
if isinstance(other, type(self)):
return type(self)(self._value | other._value)
else:
return type(self)(self._value | self.__class__(other)._value)
def __xor__(self, other):
if isinstance(other, type(self)):
return type(self)(self._value ^ other._value)
else:
return type(self)(self._value ^ self.__class__(other)._value)

_utypes = {}

def UnsignedType(bits):
"Returns a fixed-width unsigned int type with the given number of bits."
if bits in _utypes:
return _utypes[bits]
else:
class unsigned(_Integer):
__doc__ = '%d-bit unsigned integer type' % bits
def __init__(self, value):
self._value = _toFixedUnsigned(value, bits)
def __repr__(self):
return 'fixedint.UnsignedType(%d)(%d)' % (bits, self._value)
return unsigned

Byte = UnsignedType(8)
UShort = UnsignedType(16)
UInt = UnsignedType(32)
ULong = UnsignedType(64)

_stypes = {}

def SignedType(bits):
"Returns a fixed-width signed int type with the given number of bits."
if bits in _stypes:
return _stypes[bits]
else:
class signed(_Integer):
__doc__ = '%d-bit signed integer type' % bits
def __init__(self, value):
self._value = _toFixedSigned(value, bits)
def __repr__(self):
return 'fixedint.SignedType(%d)(%d)' % (bits, self._value)
return signed

SByte = SignedType(8)
Short = SignedType(16)
Int = SignedType(32)
Long = SignedType(64)