porting C code
roy at panix.com
Thu Jan 13 20:12:37 EST 2005
Lucas Raab <pythongnome at hotmail.com> wrote:
> I am currently in the process of porting some C code into Python and am
> stuck. I don't claim to be the greatest C/C++ programmer; in fact, my
> skills at C are rudimentary at best. My question is I have the
> statement: "typedef unsigned long int word32" and later on: "word32
> b" referencing the third bit of the integer.
Are you sure that's accessing the third bit? It looks to me like it's
accessing index 3 (counting from 0) of an array of ints.
> How do I do the same in Python??
In any case, if you're doing bit-fiddling in Python, you've got two
basic sets of tools.
First, the basic arithmetic operators. Boolean and (&), or (|),
left-shift (<<) and right-shift (>>) operators work in Python just like
they do in C. Integer constants starting with 0x are in hex, and the
"%x" format specifier prints integers in hex. You can play all the
normal C bit-operation tricks. To test bit 7, you can do "word & (0x1
<< 7)". To set bit 4, use "word |= (0x1 << 4)".
Second, the struct module
(http://docs.python.org/lib/module-struct.html) is useful for packing
and unpacking C structures written out into binary files.
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