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double support in Python?

Isaac To kkto at csis.hku.hk
Thu Feb 6 20:57:16 EST 2003 
>>>>> "Brandon" == Brandon Van Every <vanevery at 3DProgrammer.com> writes:

    Brandon> Um, that's like, absolutely brain-dead to a 3D game developer.
    Brandon> Does Numeric Python give you a 4-byte float type?

The only benefit of 4-byte floats on real computers is that it consumes less
space.  Computations done in 4-byte floats are seldom faster than those in
8-byte doubles (some computers convert them back and forth to 8-byte doubles
even for 4-byte floats, so they can even be slower).  But the benefit of
space efficiency is doubtful in Python, since every object uses 8 more
bytes:

#define PyObject_HEAD \
        int ob_refcnt; \
        struct _typeobject *ob_type;
#define PyObject_HEAD_INIT(type) 1, type,

so the comparison is 12-byte vs. 16-byte.

On the other hand, if you have a whole bunch of double's to store, look at
the array module.  It allows you to store a bit array of values, without
making each of them an object.  And in that array module, you can choose to
store 4-byte or 8-byte values.  When you actually get values from them, it
will wrap up the values to an object, so it is slower, but more space
efficient.

Regards,
Isaac.
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