[Python-Dev] Re: Re: Int FutureWarnings and other 2.4 TODOs
ark-mlist at att.net
Thu Dec 4 09:36:40 EST 2003
> At the risk of lapsing completely into pattern vocabulary ... an
> AbstractFactory would create Ints and bind them to a subsequently hidden
> implementation. When the int involved was tiny (-1 to 256?) this
> AbstractFactory would use one of the pre-allocated, shared (see FlyWeight)
> implementations. Outside of this range distinct Short, Long or DamnHuge
> implementations would be created.
Or, since we're talking implementation, we could use the following hack,
which I borrowed from Standard ML of New Jersey:
There is just one type, namely int.
An int is a 31-bit integer, INCLUDING sign. One extra bit indicates whether
the integer is really a number or, alternatively, a pointer to the rest of
Now, you may object that implementing this strategy in C will require lots
of shifting and masking. I would have thought so, too. However, every C
implementation of which I am aware puts all but the most trivial data
structures on boundaries of two or more bytes. This fact frees the
LOW-order bit of the integer to indicate whether it is a pointer.
So here's the strategy: If the low-order bit of an integer is *off*, it's
really a pointer to the rest of the implementation. If the low-order bit is
*on*, then it represents an integral value that can be obtained by doing a
one-bit arithmetic right shift.
Yes, it's sleazy. But I imagine it would be much faster than using
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