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Following discussions in PR #16666, this commit updates the float
formatting code to improve the `repr` reversibility, i.e. the percentage of
valid floating point numbers that do parse back to the same number when
formatted by `repr` (in CPython it's 100%).
This new code offers a choice of 3 float conversion methods, depending on
the desired tradeoff between code size and conversion precision:
- BASIC method is the smallest code footprint
- APPROX method uses an iterative method to approximate the exact
representation, which is a bit slower but but does not have a big impact
on code size. It provides `repr` reversibility on >99.8% of the cases in
double precision, and on >98.5% in single precision (except with REPR_C,
where reversibility is 100% as the last two bits are not taken into
account).
- EXACT method uses higher-precision floats during conversion, which
provides perfect results but has a higher impact on code size. It is
faster than APPROX method, and faster than the CPython equivalent
implementation. It is however not available on all compilers when using
FLOAT_IMPL_DOUBLE.
Here is the table comparing the impact of the three conversion methods on
code footprint on PYBV10 (using single-precision floats) and reversibility
rate for both single-precision and double-precision floats. The table
includes current situation as a baseline for the comparison:
PYBV10 REPR_C FLOAT DOUBLE
current = 364688 12.9% 27.6% 37.9%
basic = 364812 85.6% 60.5% 85.7%
approx = 365080 100.0% 98.5% 99.8%
exact = 366408 100.0% 100.0% 100.0%
Signed-off-by: Yoctopuce dev <dev@yoctopuce.com>
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Signed-off-by: Damien George <damien@micropython.org>
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Signed-off-by: Damien George <damien@micropython.org>
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Rework the conversion of floats to decimal strings so it aligns precisely
with the conversion of strings to floats in parsenum.c. This is to avoid
rendering 1eX as 9.99999eX-1 etc. This is achieved by removing the power-
of-10 tables and using pow() to compute the exponent directly, and that's
done efficiently by first estimating the power-of-10 exponent from the
power-of-2 exponent in the floating-point representation.
Code size is reduced by roughly 100 to 200 bytes by this commit.
Signed-off-by: Dan Ellis <dan.ellis@gmail.com>
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Formerly, py/formatfloat would print whole numbers inaccurately with
nonzero digits beyond the decimal place. This resulted from its strategy
of successive scaling of the argument by 0.1 which cannot be exactly
represented in floating point. The change in this commit avoids scaling
until the value is smaller than 1, so all whole numbers print with zero
fractional part.
Fixes issue #4212.
Signed-off-by: Dan Ellis dan.ellis@gmail.com
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These are found when building with -Wfloat-conversion.
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This is run with uncrustify 0.70.1, and black 19.10b0.
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Prior to this patch, some architectures (eg unix x86) could render floats
with "negative" digits, like ")". For example, '%.23e' % 1e-80 would come
out as "1.0000000000000000/)/(,*0e-80". This patch fixes the known cases.
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Prior to this patch, some architectures (eg unix x86) could render floats
with a ":" character in them, eg 1e+39 would come out as ":e+38" (":" is
just after "9" in ASCII so this is like 10e+38). This patch fixes some of
these cases.
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Prior to this patch the %f formatting of some FP values could be off by up
to 1, eg '%.0f' % 123 would return "122" (unix x64). Depending on the FP
precision (single vs double) certain numbers would format correctly, but
others wolud not. This patch should fix all cases of rounding for %f.
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Reduces code size by a tiny bit.
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NaN may have the sign bit set but it has no meaning, so don't print it out.
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There were several different spellings of MicroPython present in comments,
when there should be only one.
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This patch fixes 2 things when printing a floating-point number that
requires rounding up of the mantissa:
- retain the correct precision; eg 0.99 becomes 1.0, not 1.00
- if the exponent goes from -1 to 0 then render it as +0, not -0
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The if-block that this unreachable code is in has a condition "f>=5" so
"fp_isless1(f)" will always fail.
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Includes extensive test cases to catch hopefully all cases where
buffer might overflow.
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When taking the logarithm of the float to determine the exponent, there
are some edge cases that finish the log loop too large. Eg for an
input value of 1e32-epsilon, this is actually less than 1e32 from the
log-loop table and finishes as 10.0e31 when it should be 1.0e32. It
is thus rendered as :e32 (: comes after 9 in ascii).
There was the same problem with numbers less than 1.
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For single prec, exponents never get larger than about 37. For double
prec, exponents can be larger than 99 and need 3 bytes to format. This
patch makes the number of bytes needed configurable.
Addresses issue #1772.
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%f prints true integer digit, so its calculation should happen before any
exponential scaling.
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This takes previous IEEE-754 single precision float implementation, and
converts it to fully portable parametrizable implementation using C99
functions like signbit(), isnan(), isinf(). As long as those functions
are available (they can be defined in adhoc manner of course), and
compiler can perform standard arithmetic and comparison operations on a
float type, this implementation will work with any underlying float type
(including types whose mantissa is larger than available intergral integer
type).
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Fixes #1435.
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This allows using (almost) the same code for printing floats everywhere,
removes the dependency on sprintf and uses just snprintf and
applies an msvc-specific fix for snprintf in a single place so
nan/inf are now printed correctly.
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In particular, numbers which are less than 1.0 but which
round up to 1.0.
This also makes those numbers which round up to 1.0 to
print with e+00 rather than e-00 for those formats which
print exponents.
Addresses issue #1178.
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Addresses issue #1022.
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Blanket wide to all .c and .h files. Some files originating from ST are
difficult to deal with (license wise) so it was left out of those.
Also merged modpyb.h, modos.h, modstm.h and modtime.h in stmhal/.
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This adds support for almost everything (the comma isn't currently
supported).
The "unspecified" type with floats also doesn't behave exactly like
python.
Tested under unix with float and double
Spot tested on stmhal
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Remove unnecessary includes. Add includes that improve portability.
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MICROPY_ENABLE_FLOAT is automatically set in mpconfig.h if MICROPY_FLOAT_IMPL
is set to a non-zero value.
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