redo time.monotonic() to avoid double precision #343
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tannewt
reviewed
Oct 17, 2017
| return mp_obj_new_float(common_hal_time_monotonic() / 1000.0); | ||
| uint64_t time64 = common_hal_time_monotonic(); | ||
| // 4294967296 = 2^32 | ||
| return mp_obj_new_float(((uint32_t) (time64 >> 32) * 4294967296.0f + (uint32_t) (time64 & 0xffffffff)) / 1000.0f); |
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How does precision change with this? Would we get more precision by dividing by 1000.0f earlier?
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I could distribute the division among the two halves, but the precision is still lost due to single-precision floating point. So I don't believe it will make a difference:
>>> (2.0**22+1)/1000 - (2.0**22+0)/1000
0.0
>>> (2.0**22+2)/1000 - (2.0**22+1)/1000
0.00195313
>>> (2.0**22+3)/1000 - (2.0**22+2)/1000
0.0
>>> (2.0**22+4)/1000 - (2.0**22+3)/1000
0.00195313
>>>
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This is awesome! Would you mind waiting to add framebuf until 3.x? It'll
give us some code size flexibility with 3.x.
…On Mon, Oct 16, 2017 at 8:53 PM Dan Halbert ***@***.***> wrote:
Gains back 3044 bytes! Framebuf would now fit, with 56 bytes to spare,
before any -finline-limit trickery.
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You can view, comment on, or merge this pull request online at:
#343
Commit Summary
- Set DRVSTR on output pins to strong (more current capability).
- redo time.monotonic() to avoid double precision
File Changes
- *M* atmel-samd/common-hal/digitalio/DigitalInOut.c
<https://github.com/adafruit/circuitpython/pull/343/files#diff-0> (3)
- *M* shared-bindings/time/__init__.c
<https://github.com/adafruit/circuitpython/pull/343/files#diff-1> (4)
Patch Links:
- https://github.com/adafruit/circuitpython/pull/343.patch
- https://github.com/adafruit/circuitpython/pull/343.diff
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Deferring is fine with me, to 2.2 or 3.0. Limor would like to change the font in framebuf from 8x8 to 8x5 anyway. |
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Gains back 3044 bytes! Framebuf would now fit in non-Express, with 56 bytes to spare, before any
-finline-limittrickery. Implements #342.