8000 BUG: Unexpected result in uint8 division on x86 · Issue #19045 · numpy/numpy · GitHub
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BUG: Unexpected result in uint8 division on x86 #19045

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seiko2plus opened this issue May 19, 2021 · 0 comments · Fixed by #19046
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BUG: Unexpected result in uint8 division on x86 #19045

seiko2plus opened this issue May 19, 2021 · 0 comments · Fixed by #19046
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00 - Bug 06 - Regression component: SIMD Issues in SIMD (fast instruction sets) code or machinery
Milestone
1.21.0 release

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@seiko2plus
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The bug can occur in special cases e.g. when the divisor is scalar and equal to 9 or 13 and the dividend is array contains consecutive duplicate values of 233.

Reproducing code example:

>>> import numpy as np
>>> a = np.full(64, 233, dtype=np.uint8)
>>> a // 9
array([25, 26, 25, 26, 25, 26, 25, 26, 25, 26, 25, 26, 25, 26, 25, 26, 25,
       26, 25, 26, 25, 26, 25, 26, 25, 26, 25, 26, 25, 26, 25, 26, 25, 26,
       25, 26, 25, 26, 25, 26, 25, 26, 25, 26, 25, 26, 25, 26, 25, 26, 25,
       26, 25, 26, 25, 26, 25, 26, 25, 26, 25, 26, 25, 26], dtype=uint8)

NumPy/Python version information:

main, after #18075. related to #18178
@seiko2plus seiko2plus added 00 - Bug component: SIMD Issues in SIMD (fast instruction sets) code or machinery labels May 19, 2021
@seiko2plus seiko2plus mentioned this issue May 19, 2021
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@seberg seberg added this to the 1.21.0 release milestone May 19, 2021
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BUG, SIMD: Fix unexpected result of uint8 division on X86 seiko2plus/numpy
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