dbbaa959c8
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>
43 lines
747 B
Python
43 lines
747 B
Python
# Test struct pack/unpack with 'e' typecode.
|
|
|
|
try:
|
|
import struct
|
|
except ImportError:
|
|
print("SKIP")
|
|
raise SystemExit
|
|
|
|
test_values = (
|
|
1e-7,
|
|
2e-7,
|
|
1e-6,
|
|
1e-5,
|
|
1e-4,
|
|
1e-3,
|
|
1e-2,
|
|
0.1,
|
|
0,
|
|
1,
|
|
2,
|
|
4,
|
|
8,
|
|
10,
|
|
100,
|
|
1e3,
|
|
1e4,
|
|
6e4,
|
|
float("inf"),
|
|
)
|
|
|
|
for j in test_values:
|
|
for i in (j, -j):
|
|
x = struct.pack("<e", i)
|
|
v = struct.unpack("<e", x)[0]
|
|
print("%.7f %s %.5f %s" % (i, x, v, i == v))
|
|
|
|
# In CPython, packing a float that doesn't fit into a half-float raises OverflowError.
|
|
# But in MicroPython it does not, but rather stores the value as inf.
|
|
# This test is here for coverage.
|
|
try:
|
|
struct.pack("e", 1e15)
|
|
except OverflowError:
|
|
pass
|