Yes, I just want to write code which is portable (as for example that `& ...`) but still favors PyPy. On Mon, Apr 4, 2016 at 3:49 PM, Maciej Fijalkowski <fijall@gmail.com> wrote:
right, so there is no way to get wrap-around arithmetics in cpython without modifications
On Mon, Apr 4, 2016 at 3:48 PM, Tuom Larsen <tuom.larsen@gmail.com> wrote:
I would like to avoid numpy, if possible. Even if it might be bundled with PyPy (is it?) I still would like the code to run in CPython with no dependencies.
On Mon, Apr 4, 2016 at 3:45 PM, Maciej Fijalkowski <fijall@gmail.com> wrote:
so numpy64 will give you wrap-around arithmetics. What else are you looking for? :-)
On Mon, Apr 4, 2016 at 3:38 PM, Tuom Larsen <tuom.larsen@gmail.com> wrote:
You mean I should first store the result into numpy's `int64`, and then to `array.array`? Like:
x = int64(2**63 << 1) a[0] = x
Or:
x = int64(2**63) x[0] = x << 1
What the "real types" goes, is this the only option?
Thanks in any case!
On Mon, Apr 4, 2016 at 3:32 PM, Maciej Fijalkowski <fijall@gmail.com> wrote:
one option would be to use integers from _numpypy module:
from numpy import int64 after installing numpy.
There are obscure ways to get it without installing numpy. Another avenue would be to use __pypy__.intop.int_mul etc.
Feel free to complain "no, I want real types that I can work with" :-)
Cheers, fijal
On Mon, Apr 4, 2016 at 3:10 PM, Tuom Larsen <tuom.larsen@gmail.com> wrote:
Hello!
Suppose I'm on 64-bit machine and there is an `a = arrar.array('L', [0])` (item size is 8 bytes). In Python, when an integer does not fit machine width it gets promoted to "long" integer of arbitrary size. So this will fail:
a[0] = 2**63 << 1
To fix this, one could instead write:
a[0] = (2**63 << 1) & (2**64 - 1)
My question is, when I know that the result will be stored in `array.array` anyway, how to prevent the promotion to long integers? What is the most performat way to perform such calculations? Is PyPy able to optimize away that `& (2**64 - 1)` when I use `'L'` typecode?
I mean, in C I wouldn't have to worry about it as everything above the 63rd bit will be simply cut off. I would like to help PyPy to generate the best possible code, does anyone have some suggestions please?
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