From dbbaa959c85c04dbbcde5908b5d0775b574e44e7 Mon Sep 17 00:00:00 2001 From: Yoctopuce dev Date: Fri, 6 Jun 2025 14:55:21 +0200 Subject: py/formatfloat: Improve accuracy of float formatting code. 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 --- tests/float/string_format_modulo3.py | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'tests/float/string_format_modulo3.py') diff --git a/tests/float/string_format_modulo3.py b/tests/float/string_format_modulo3.py index f9d9c43cd..f8aeeda20 100644 --- a/tests/float/string_format_modulo3.py +++ b/tests/float/string_format_modulo3.py @@ -1,3 +1,3 @@ -# uPy and CPython outputs differ for the following +# Test corner cases where MicroPython and CPython outputs used to differ in the past print("%.1g" % -9.9) # round up 'g' with '-' sign print("%.2g" % 99.9) # round up -- cgit v1.2.3