float: Introduce MICROPY_FLOAT_BOX_AS_NEEDED. #18413
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In REPR_C, only 1/4 of all C `float` values can be expressed, depending on the least significant bits of the mantissa. As an alternative to discarding the low bits, BOX_AS_NEEDED boxes values that would not otherwise be representable. Signed-off-by: Jeff Epler <[email protected]>
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## master #18413 +/- ##
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Hits 21933 21933
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Signed-off-by: Jeff Epler <[email protected]>
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Summary
In REPR_C, only 1/4 of all C
floatvalues can be expressed, depending on the least significant bits of the mantissa.As an alternative to discarding the low bits, BOX_AS_NEEDED boxes values that would not otherwise be representable.
Testing
I ran the unix
make VARIANT=longlong testlocally, and ranci stm32_misc_buildto check that REPR_C builds without BOX_AS_NEEDED still compiled.However,
build-longlong/micropython -X emit=native tests/thread/stress_schedule.pyconsistently fails on my local system before and after this change so I wasn't able to run all longlong tests, just themake testones.Trade-offs and Alternatives
#18401 introduced a whole new REPR, a design which had some good points but which reduced the unboxed integer precision by 1 bit.