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only apply mask to _led_buffer if < 256 #9

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Merged
tannewt merged 2 commits into from
Oct 17, 2018
Merged

only apply mask to _led_buffer if < 256 #9

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eb1f0a8
only apply mask to _led_buffer if < 256
Oct 11, 2018
5151423
replace conditional with bitwise and, per @tannewt
Oct 17, 2018
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3 changes: 2 additions & 1 deletion adafruit_trellis.py
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Original file line number Diff line number Diff line change
Expand Up @@ -91,7 +91,8 @@ def __setitem__(self, x, value):
led = ledLUT[x % 16] >> 4
mask = 1 << (ledLUT[x % 16] & 0x0f)
if value:
self._parent._led_buffer[x // 16][(led * 2) + 1] |= mask
if mask < 256:
self._parent._led_buffer[x // 16][(led * 2) + 1] |= mask
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@tannewt tannewt Oct 12, 2018

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I believe this will fix it because you know above that only one bit is set. However, its probably simpler this way:

self._parent._led_buffer[x // 16][(led * 2) + 1] |= (mask & 0xff)

This only allows bits in the first byte (0xff) to be preserved. The next line below drops those bits by shifting them off the right side.

self._parent._led_buffer[x // 16][(led * 2) + 2] |= mask >> 8
elif not value:
self._parent._led_buffer[x // 16][(led * 2) + 1] &= ~mask
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