On 6/7/2015 10:33 AM, Chris Angelico wrote:
The negative result is a strong indicator that you're not seeing the
results of rand() here. While there is a potential for bias (check out
RAND_MAX, and consider that there may be some small bias there;
although on most modern systems, RAND_MAX is going to be high enough
that the bias from modulo 6 won't be highly visible), it's much MUCH
more likely that you're looking at uninitialized memory.
Here's the revised Cython code.
cdef extern from "stdlib.h":
int c_libc_rand "rand"()
cdef int f[12]
def roll(int x):
cdef:
int a = 0, b = 0, i = 0
for i in range(x):
a = c_libc_rand() % 6 + 1
b = c_libc_rand() % 6 + 1
f[(a + b) - 1] += 1
return f
Here's the new console output.
PS Z:\projects\programming\python\basic_games\fastdice> python test_fastdice.py
TOTAL SPOTS NUMBER OF TIMES
2 1389911
3 2777722
4 4168248
5 5553632
6 6944907
7 8334670
8 6945597
9 5553557
10 4167485
11 2775806
12 1388465
1.65599989891
I had to put the array definition outside of the function declaration,
where it's automatically initialized to zero in the global space. I
tried to initialize the array from inside the function but Cython threw
up errors, either the C declaration wasn't correct or unable to convert
from C to Python when updating the array elements. I'll figure out that
problem later. The new version works as expected.
Thanks,
Chris R.
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