py/parse: Add support for math module constants and float folding.

Add a new MICROPY_COMP_CONST_FLOAT feature, enabled by in mpy-cross and
when compiling with MICROPY_CONFIG_ROM_LEVEL_CORE_FEATURES.  The new
feature leverages the code of MICROPY_COMP_CONST_FOLDING to support folding
of floating point constants.

If MICROPY_COMP_MODULE_CONST is defined as well, math module constants are
made available at compile time. For example:

    _DEG_TO_GRADIANT = const(math.pi / 180)
    _INVALID_VALUE = const(math.nan)

A few corner cases had to be handled:
- The float const folding code should not fold expressions resulting into
  complex results, as the mpy parser for complex immediates has
  limitations.
- The constant generation code must distinguish between -0.0 and 0.0, which
  are different even if C consider them as ==.

This change removes previous limitations on the use of `const()`
expressions that would result in floating point number, so the test cases
of micropython/const_error have to be updated.

Additional test cases have been added to cover the new repr() code (from a
previous commit).  A few other simple test cases have been added to handle
the use of floats in `const()` expressions, but the float folding code
itself is also tested when running general float test cases, as float
expressions often get resolved at compile-time (with this change).

Signed-off-by: Yoctopuce dev <dev@yoctopuce.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/tests/micropython/const_float.py b/tests/micropython/const_float.py
new file mode 100644
index 000000000..c3a0df027
--- /dev/null
+++ b/tests/micropython/const_float.py
@@ -0,0 +1,23 @@
+# test constant optimisation, with consts that are floats
+
+from micropython import const
+
+# check we can make consts from floats
+F1 = const(2.5)
+F2 = const(-0.3)
+print(type(F1), F1)
+print(type(F2), F2)
+
+# check arithmetic with floats
+F3 = const(F1 + F2)
+F4 = const(F1**2)
+print(F3, F4)
+
+# check int operations with float results
+F5 = const(1 / 2)
+F6 = const(2**-2)
+print(F5, F6)
+
+# note: we also test float expression folding when
+#       we're compiling test cases in tests/float, as
+#       many expressions are resolved at compile time.