Daniel Stutzbach <dan...@stutzbachenterprises.com> added the comment:
After experimenting with changing the order of the multiplications and not
having much luck, I went back and looked for other differences in Alexander's
Python functions that might cause the speed difference. I believe
partial_product2 is fast because it performs all of its operations in-place
using a single list, whereas partial_product3 creates a new list during each
iteration. Here's a version of partial_product3 that operates in-place and is
just as fast as partial_product2:
def partial_product3(j, i):
a = [l << 1 | 1 for l in range(j, i + 1)]
n = len(a)
while 1:
if n == 1:
return a[0]
half = n//2
for k in range(0,half):
a[k] = a[k*2] * a[k*2+1]
if n & 1:
a[half] = a[n-1]
n = half
----------
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue8692>
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