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Benjamin Root

28 Apr 2015 28 Apr '15

4 p.m.

I have a need to have a numpy array of 17 byte (more specifically, at least 147 bits) values that I would be doing some bit twiddling on. I have found that doing a dtype of "i17" yields a dtype of int32, which is completely not what I intended. Doing 'u17' gets an "data type not understood". I have tried 'a17', but then bitwise_or() and left_shift() do not work (returns "NotImplemented"). How should I be going about this? Cheers! Ben Root

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Jaime Fernández del Río

28 Apr 28 Apr

4:19 p.m.

New subject: how to set a fixed sized dtype suitable for bitwise operations

On Tue, Apr 28, 2015 at 7:00 AM, Benjamin Root wrote:

I have a need to have a numpy array of 17 byte (more specifically, at least 147 bits) values that I would be doing some bit twiddling on. I have found that doing a dtype of "i17" yields a dtype of int32, which is completely not what I intended. Doing 'u17' gets an "data type not understood". I have tried 'a17', but then bitwise_or() and left_shift() do not work (returns "NotImplemented").

How should I be going about this?

The correct type to use would be a void dtype:

...
...
dt = np.dtype('V17') dt.itemsize 17

Unfortunately, it does not support bitwise operations either, which seems like an oddity to me:

...
...
a = np.empty(2, dt) a[0] = 'abcdef' a[1] = bytearray([64, 56, 78]) a[0] | a[1] Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for |: 'numpy.void' and 'numpy.void'

Any fundamental reason for this? Jaime -- (\__/) ( O.o) ( > <) Este es Conejo. Copia a Conejo en tu firma y ayúdale en sus planes de dominación mundial.

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Benjamin Root

5:59 p.m.

New subject: how to set a fixed sized dtype suitable for bitwise operations

Yeah, I am not seeing any way around it at the moment. I guess I will have to use the bitarray package for now. I was hoping for some fast per-element processing, but at the moment, I guess I will have to sacrifice that just to have something that worked correctly. Ben Root On Tue, Apr 28, 2015 at 10:19 AM, Jaime Fernández del Río < jaime.frio@gmail.com> wrote:

On Tue, Apr 28, 2015 at 7:00 AM, Benjamin Root wrote:

...
I have a need to have a numpy array of 17 byte (more specifically, at least 147 bits) values that I would be doing some bit twiddling on. I have found that doing a dtype of "i17" yields a dtype of int32, which is completely not what I intended. Doing 'u17' gets an "data type not understood". I have tried 'a17', but then bitwise_or() and left_shift() do not work (returns "NotImplemented").

...
How should I be going about this?

The correct type to use would be a void dtype:

...
...
...
dt = np.dtype('V17') dt.itemsize 17

Unfortunately, it does not support bitwise operations either, which seems like an oddity to me:

...
...
...
a = np.empty(2, dt) a[0] = 'abcdef' a[1] = bytearray([64, 56, 78]) a[0] | a[1] Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for |: 'numpy.void' and 'numpy.void'

Any fundamental reason for this?

Jaime

-- (\__/) ( O.o) ( > <) Este es Conejo. Copia a Conejo en tu firma y ayúdale en sus planes de dominación mundial.

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