[moving this to cython-users]
Christian Inci, 24.01.2013 15:13:
> Subject: Feature Request: expand list/tuple in 'if (... in ...):' ...
>
> expand list/tuple in 'if (... in ...):' on compile-time if the list/tuple
> contains only static values.
>
> test1: list is expanded manually.
> test2: list is not expanded.
>
> The output of the testcase is:
> test1: timediff: 0.205533
> test2: timediff: 17.567185
>
>
> Testcase:
>
> from time import time
>
> cdef tuple INT_TUPLE = (0x66, 0x67, 0x2e,
> 0x36, 0x3e, 0x26, 0x64,
> 0x65, 0xf2, 0xf3, 0xf0)
>
> cpdef test():
> cdef unsigned int i
> cdef unsigned short j # 'unsigned char j' won't work for some reason
> cdef double start_time
> start_time = time()
> for i in range(0x50000):
> for j in range(256):
> if (j == 0x66 or j == 0x67 or j == 0x2e or j == 0x36 or j == 0x3e
> or j == 0x26 or j == 0x64 or j == 0x65 or j == 0xf2 or j == 0xf3 or j ==
> 0xf0):
> pass
> print("test1: timediff: {0:f}".format(time()-start_time))
> start_time = time()
> for i in range(0x50000):
> for j in range(256):
> if (j in INT_TUPLE):
> pass
> print("test2: timediff: {0:f}".format(time()-start_time))
This is not an optimisation as it might render the code incorrect. How can
Cython know that you'll never change INT_TUPLE at runtime?
However, if you use a literal list or tuple in place, this already works,
i.e. the first example is equivalent to
if j in (0x66, 0x67, 0x2e,
0x36, 0x3e, 0x26, 0x64,
0x65, 0xf2, 0xf3, 0xf0):
You actually get a C switch statement for it.
If you prefer keeping the set of integer values at a separate place, this
should work:
DEF INT_TUPLE = (0x66, 0x67, 0x2e,
0x36, 0x3e, 0x26, 0x64,
0x65, 0xf2, 0xf3, 0xf0)
(mind the upper case "DEF").
Stefan
_______________________________________________
cython-devel mailing list
cython-devel@python.org
http://mail.python.org/mailman/listinfo/cython-devel
