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BUG: inaccurate 8-bit unsigned integer division when the divisor is a scalar #20168

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seiko2plus opened this issue Oct 23, 2021 · 1 comment · Fixed by #20153
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BUG: inaccurate 8-bit unsigned integer division when the divisor is a scalar #20168

seiko2plus opened this issue Oct 23, 2021 · 1 comment · Fixed by #20153
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00 - Bug component: SIMD Issues in SIMD (fast instruction sets) code or machinery

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@seiko2plus
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seiko2plus commented Oct 23, 2021 •
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Describe the issue:

The bug appears when the divisor is a scalar, ceil(log2(divisor)) == 8 and the dividend length >= 64 or 32 or 16 depend on the enabled SIMD extension e.g. on AVX2 length >= 32

Reproduce the code example:

>>> import numpy as np
>>> np.arange(0, 32, dtype=np.uint8) // 132 # ceil(log2(132)) == 8
array([0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
       1, 0, 1, 0, 1, 0, 1, 0, 1, 0], dtype=uint8)
>>> # while it should return the following instead
>>> np.arange(0, 32, dtype=np.uint16) // 132
array([0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
       0, 0, 0, 0, 0, 0, 0, 0, 0, 0], dtype=uint16)

Error message:

No response

NumPy/Python version information:

1.21.3 3.9.5 (default, May 19 2021, 11:32:47)
[GCC 10.2.0]

related to #20025, #18766, #18178
@seiko2plus seiko2plus added 00 - Bug component: SIMD Issues in SIMD (fast instruction sets) code or machinery labels Oct 23, 2021
@seiko2plus seiko2plus mentioned this issue Oct 23, 2021
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@seiko2plus seiko2plus modified the milestones: 1.21.3 release, 1.21.4 Oct 23, 2021
@seiko2plus seiko2plus mentioned this issue Oct 23, 2021
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@seiko2plus seiko2plus linked a pull request Oct 27, 2021 that will close this issue
BUG, SIMD: Fix 64-bit/8-bit integer division by a scalar #20153
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@seiko2plus
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fixed by #20153.

@charris charris mentioned this issue Nov 3, 2021
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00 - Bug component: SIMD Issues in SIMD (fast instruction sets) code or machinery
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BUG, SIMD: Fix 64-bit/8-bit integer division by a scalar numpy/numpy
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@seiko2plus