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>

12 files changed, 143 insertions, 31 deletions

diff --git a/mpy-cross/mpconfigport.h b/mpy-cross/mpconfigport.h
index 94a598c99..81cbfc2ee 100644
--- a/mpy-cross/mpconfigport.h
+++ b/mpy-cross/mpconfigport.h
@@ -55,6 +55,7 @@
 #define MICROPY_COMP_CONST_FOLDING  (1)
 #define MICROPY_COMP_MODULE_CONST   (1)
 #define MICROPY_COMP_CONST          (1)
+#define MICROPY_COMP_CONST_FLOAT    (1)
 #define MICROPY_COMP_DOUBLE_TUPLE_ASSIGN (1)
 #define MICROPY_COMP_TRIPLE_TUPLE_ASSIGN (1)
 #define MICROPY_COMP_RETURN_IF_EXPR (1)
@@ -88,7 +89,8 @@
 #define MICROPY_PY_ARRAY            (0)
 #define MICROPY_PY_ATTRTUPLE        (0)
 #define MICROPY_PY_COLLECTIONS      (0)
-#define MICROPY_PY_MATH             (0)
+#define MICROPY_PY_MATH             (MICROPY_COMP_CONST_FLOAT)
+#define MICROPY_PY_MATH_CONSTANTS   (MICROPY_COMP_CONST_FLOAT)
 #define MICROPY_PY_CMATH            (0)
 #define MICROPY_PY_GC               (0)
 #define MICROPY_PY_IO               (0)
diff --git a/py/builtin.h b/py/builtin.h
index 6efe3e8fa..388bc8470 100644
--- a/py/builtin.h
+++ b/py/builtin.h
@@ -138,6 +138,7 @@ extern const mp_obj_module_t mp_module_sys;
 extern const mp_obj_module_t mp_module_errno;
 extern const mp_obj_module_t mp_module_uctypes;
 extern const mp_obj_module_t mp_module_machine;
+extern const mp_obj_module_t mp_module_math;
 
 extern const char MICROPY_PY_BUILTINS_HELP_TEXT[];
 
diff --git a/py/emitcommon.c b/py/emitcommon.c
index a9eb6e202..1f701db80 100644
--- a/py/emitcommon.c
+++ b/py/emitcommon.c
@@ -25,6 +25,7 @@
  */
 
 #include <assert.h>
+#include <math.h>
 
 #include "py/emit.h"
 #include "py/nativeglue.h"
@@ -72,7 +73,21 @@ static bool strictly_equal(mp_obj_t a, mp_obj_t b) {
         }
         return true;
     } else {
-        return mp_obj_equal(a, b);
+        if (!mp_obj_equal(a, b)) {
+            return false;
+        }
+        #if MICROPY_PY_BUILTINS_FLOAT && MICROPY_COMP_CONST_FLOAT
+        if (a_type == &mp_type_float) {
+            mp_float_t a_val = mp_obj_float_get(a);
+            if (a_val == (mp_float_t)0.0) {
+                // Although 0.0 == -0.0, they are not strictly_equal and
+                // must be stored as two different constants in .mpy files
+                mp_float_t b_val = mp_obj_float_get(b);
+                return signbit(a_val) == signbit(b_val);
+            }
+        }
+        #endif
+        return true;
     }
 }
 
diff --git a/py/mpconfig.h b/py/mpconfig.h
index caa63fef3..ed5ccccb6 100644
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -490,6 +490,13 @@
 #define MICROPY_COMP_CONST (MICROPY_CONFIG_ROM_LEVEL_AT_LEAST_CORE_FEATURES)
 #endif
 
+// Whether to enable float constant folding like 1.2+3.4 (when MICROPY_COMP_CONST_FOLDING is also enabled)
+// and constant optimisation like id = const(1.2) (when MICROPY_COMP_CONST is also enabled)
+// and constant lookup like math.inf (when MICROPY_COMP_MODULE_CONST is also enabled)
+#ifndef MICROPY_COMP_CONST_FLOAT
+#define MICROPY_COMP_CONST_FLOAT (MICROPY_CONFIG_ROM_LEVEL_AT_LEAST_CORE_FEATURES)
+#endif
+
 // Whether to enable optimisation of: a, b = c, d
 // Costs 124 bytes (Thumb2)
 #ifndef MICROPY_COMP_DOUBLE_TUPLE_ASSIGN
diff --git a/py/parse.c b/py/parse.c
index db89fb584..91eea3e36 100644
--- a/py/parse.c
+++ b/py/parse.c
@@ -336,18 +336,34 @@ static uint8_t peek_rule(parser_t *parser, size_t n) {
 }
 #endif
 
-bool mp_parse_node_get_int_maybe(mp_parse_node_t pn, mp_obj_t *o) {
+#if MICROPY_COMP_CONST_FOLDING || MICROPY_EMIT_INLINE_ASM
+static bool mp_parse_node_get_number_maybe(mp_parse_node_t pn, mp_obj_t *o) {
     if (MP_PARSE_NODE_IS_SMALL_INT(pn)) {
         *o = MP_OBJ_NEW_SMALL_INT(MP_PARSE_NODE_LEAF_SMALL_INT(pn));
         return true;
     } else if (MP_PARSE_NODE_IS_STRUCT_KIND(pn, RULE_const_object)) {
         mp_parse_node_struct_t *pns = (mp_parse_node_struct_t *)pn;
         *o = mp_parse_node_extract_const_object(pns);
-        return mp_obj_is_int(*o);
+        return mp_obj_is_int(*o)
+               #if MICROPY_COMP_CONST_FLOAT
+               || mp_obj_is_float(*o)
+               #endif
+        ;
     } else {
         return false;
     }
 }
+#endif
+
+#if MICROPY_EMIT_INLINE_ASM
+bool mp_parse_node_get_int_maybe(mp_parse_node_t pn, mp_obj_t *o) {
+    return mp_parse_node_get_number_maybe(pn, o)
+           #if MICROPY_COMP_CONST_FLOAT
+           && mp_obj_is_int(*o)
+           #endif
+    ;
+}
+#endif
 
 #if MICROPY_COMP_CONST_TUPLE || MICROPY_COMP_CONST
 static bool mp_parse_node_is_const(mp_parse_node_t pn) {
@@ -642,12 +658,32 @@ static const mp_rom_map_elem_t mp_constants_table[] = {
     #if MICROPY_PY_UCTYPES
     { MP_ROM_QSTR(MP_QSTR_uctypes), MP_ROM_PTR(&mp_module_uctypes) },
     #endif
+    #if MICROPY_PY_BUILTINS_FLOAT && MICROPY_PY_MATH && MICROPY_COMP_CONST_FLOAT
+    { MP_ROM_QSTR(MP_QSTR_math), MP_ROM_PTR(&mp_module_math) },
+    #endif
     // Extra constants as defined by a port
     MICROPY_PORT_CONSTANTS
 };
 static MP_DEFINE_CONST_MAP(mp_constants_map, mp_constants_table);
 #endif
 
+static bool binary_op_maybe(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs, mp_obj_t *res) {
+    nlr_buf_t nlr;
+    if (nlr_push(&nlr) == 0) {
+        mp_obj_t tmp = mp_binary_op(op, lhs, rhs);
+        #if MICROPY_PY_BUILTINS_COMPLEX
+        if (mp_obj_is_type(tmp, &mp_type_complex)) {
+            return false;
+        }
+        #endif
+        *res = tmp;
+        nlr_pop();
+        return true;
+    } else {
+        return false;
+    }
+}
+
 static bool fold_logical_constants(parser_t *parser, uint8_t rule_id, size_t *num_args) {
     if (rule_id == RULE_or_test
         || rule_id == RULE_and_test) {
@@ -706,7 +742,7 @@ static bool fold_logical_constants(parser_t *parser, uint8_t rule_id, size_t *nu
 }
 
 static bool fold_constants(parser_t *parser, uint8_t rule_id, size_t num_args) {
-    // this code does folding of arbitrary integer expressions, eg 1 + 2 * 3 + 4
+    // this code does folding of arbitrary numeric expressions, eg 1 + 2 * 3 + 4
     // it does not do partial folding, eg 1 + 2 + x -> 3 + x
 
     mp_obj_t arg0;
@@ -716,7 +752,7 @@ static bool fold_constants(parser_t *parser, uint8_t rule_id, size_t num_args) {
         || rule_id == RULE_power) {
         // folding for binary ops: | ^ & **
         mp_parse_node_t pn = peek_result(parser, num_args - 1);
-        if (!mp_parse_node_get_int_maybe(pn, &arg0)) {
+        if (!mp_parse_node_get_number_maybe(pn, &arg0)) {
             return false;
         }
         mp_binary_op_t op;
@@ -732,58 +768,61 @@ static bool fold_constants(parser_t *parser, uint8_t rule_id, size_t num_args) {
         for (ssize_t i = num_args - 2; i >= 0; --i) {
             pn = peek_result(parser, i);
             mp_obj_t arg1;
-            if (!mp_parse_node_get_int_maybe(pn, &arg1)) {
+            if (!mp_parse_node_get_number_maybe(pn, &arg1)) {
                 return false;
             }
+            #if !MICROPY_COMP_CONST_FLOAT
             if (op == MP_BINARY_OP_POWER && mp_obj_int_sign(arg1) < 0) {
                 // ** can't have negative rhs
                 return false;
             }
-            arg0 = mp_binary_op(op, arg0, arg1);
+            #endif
+            if (!binary_op_maybe(op, arg0, arg1, &arg0)) {
+                return false;
+            }
         }
     } else if (rule_id == RULE_shift_expr
                || rule_id == RULE_arith_expr
                || rule_id == RULE_term) {
         // folding for binary ops: << >> + - * @ / % //
         mp_parse_node_t pn = peek_result(parser, num_args - 1);
-        if (!mp_parse_node_get_int_maybe(pn, &arg0)) {
+        if (!mp_parse_node_get_number_maybe(pn, &arg0)) {
             return false;
         }
         for (ssize_t i = num_args - 2; i >= 1; i -= 2) {
             pn = peek_result(parser, i - 1);
             mp_obj_t arg1;
-            if (!mp_parse_node_get_int_maybe(pn, &arg1)) {
+            if (!mp_parse_node_get_number_maybe(pn, &arg1)) {
                 return false;
             }
             mp_token_kind_t tok = MP_PARSE_NODE_LEAF_ARG(peek_result(parser, i));
-            if (tok == MP_TOKEN_OP_AT || tok == MP_TOKEN_OP_SLASH) {
-                // Can't fold @ or /
+            if (tok == MP_TOKEN_OP_AT) {
+                // Can't fold @
+                return false;
+            }
+            #if !MICROPY_COMP_CONST_FLOAT
+            if (tok == MP_TOKEN_OP_SLASH) {
+                // Can't fold /
                 return false;
             }
+            #endif
             mp_binary_op_t op = MP_BINARY_OP_LSHIFT + (tok - MP_TOKEN_OP_DBL_LESS);
-            int rhs_sign = mp_obj_int_sign(arg1);
-            if (op <= MP_BINARY_OP_RSHIFT) {
-                // << and >> can't have negative rhs
-                if (rhs_sign < 0) {
-                    return false;
-                }
-            } else if (op >= MP_BINARY_OP_FLOOR_DIVIDE) {
-                // % and // can't have zero rhs
-                if (rhs_sign == 0) {
-                    return false;
-                }
+            if (!binary_op_maybe(op, arg0, arg1, &arg0)) {
+                return false;
             }
-            arg0 = mp_binary_op(op, arg0, arg1);
         }
     } else if (rule_id == RULE_factor_2) {
         // folding for unary ops: + - ~
         mp_parse_node_t pn = peek_result(parser, 0);
-        if (!mp_parse_node_get_int_maybe(pn, &arg0)) {
+        if (!mp_parse_node_get_number_maybe(pn, &arg0)) {
             return false;
         }
         mp_token_kind_t tok = MP_PARSE_NODE_LEAF_ARG(peek_result(parser, 1));
         mp_unary_op_t op;
         if (tok == MP_TOKEN_OP_TILDE) {
+            if (!mp_obj_is_int(arg0)) {
+                return false;
+            }
             op = MP_UNARY_OP_INVERT;
         } else {
             assert(tok == MP_TOKEN_OP_PLUS || tok == MP_TOKEN_OP_MINUS); // should be
@@ -855,7 +894,7 @@ static bool fold_constants(parser_t *parser, uint8_t rule_id, size_t num_args) {
             return false;
         }
         // id1.id2
-        // look it up in constant table, see if it can be replaced with an integer
+        // look it up in constant table, see if it can be replaced with an integer or a float
         mp_parse_node_struct_t *pns1 = (mp_parse_node_struct_t *)pn1;
         assert(MP_PARSE_NODE_IS_ID(pns1->nodes[0]));
         qstr q_base = MP_PARSE_NODE_LEAF_ARG(pn0);
@@ -866,7 +905,7 @@ static bool fold_constants(parser_t *parser, uint8_t rule_id, size_t num_args) {
         }
         mp_obj_t dest[2];
         mp_load_method_maybe(elem->value, q_attr, dest);
-        if (!(dest[0] != MP_OBJ_NULL && mp_obj_is_int(dest[0]) && dest[1] == MP_OBJ_NULL)) {
+        if (!(dest[0] != MP_OBJ_NULL && (mp_obj_is_int(dest[0]) || mp_obj_is_float(dest[0])) && dest[1] == MP_OBJ_NULL)) {
             return false;
         }
         arg0 = dest[0];
diff --git a/tests/float/float_parse_doubleprec.py b/tests/float/float_parse_doubleprec.py
index 81fcadcee..c1b0b4823 100644
--- a/tests/float/float_parse_doubleprec.py
+++ b/tests/float/float_parse_doubleprec.py
@@ -19,3 +19,9 @@ print("%.14e" % float("." + "0" * 400 + "9e400"))
 print(float("1.00000000000000000000e-307"))
 print(float("10.0000000000000000000e-308"))
 print(float("100.000000000000000000e-309"))
+
+# ensure repr() adds an extra digit when needed for accurate parsing
+print(float(repr(float("2.0") ** 100)) == float("2.0") ** 100)
+
+# ensure repr does not add meaningless extra digits (1.234999999999)
+print(repr(1.2345))
diff --git a/tests/micropython/const_error.py b/tests/micropython/const_error.py
index d35be530a..950360e4d 100644
--- a/tests/micropython/const_error.py
+++ b/tests/micropython/const_error.py
@@ -18,8 +18,6 @@ test_syntax("A = const(1); A = const(2)")
 
 # these operations are not supported within const
 test_syntax("A = const(1 @ 2)")
-test_syntax("A = const(1 / 2)")
-test_syntax("A = const(1 ** -2)")
 test_syntax("A = const(1 << -2)")
 test_syntax("A = const(1 >> -2)")
 test_syntax("A = const(1 % 0)")
diff --git a/tests/micropython/const_error.py.exp b/tests/micropython/const_error.py.exp
index 3edc3efe9..bef69eb32 100644
--- a/tests/micropython/const_error.py.exp
+++ b/tests/micropython/const_error.py.exp
@@ -5,5 +5,3 @@ SyntaxError
 SyntaxError
 SyntaxError
 SyntaxError
-SyntaxError
-SyntaxError
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.
diff --git a/tests/micropython/const_float.py.exp b/tests/micropython/const_float.py.exp
new file mode 100644
index 000000000..17a86a6d9
--- /dev/null
+++ b/tests/micropython/const_float.py.exp
@@ -0,0 +1,4 @@
+<class 'float'> 2.5
+<class 'float'> -0.3
+2.2 6.25
+0.5 0.25
diff --git a/tests/micropython/const_math.py b/tests/micropython/const_math.py
new file mode 100644
index 000000000..7ee5edc6d
--- /dev/null
+++ b/tests/micropython/const_math.py
@@ -0,0 +1,18 @@
+# Test expressions based on math module constants
+try:
+    import math
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+from micropython import const
+
+# check that we can make consts from math constants
+# (skip if the target has MICROPY_COMP_MODULE_CONST disabled)
+try:
+    exec("two_pi = const(2.0 * math.pi)")
+except SyntaxError:
+    print("SKIP")
+    raise SystemExit
+
+print(math.cos(two_pi))
diff --git a/tests/micropython/const_math.py.exp b/tests/micropython/const_math.py.exp
new file mode 100644
index 000000000..d3827e75a
--- /dev/null
+++ b/tests/micropython/const_math.py.exp
@@ -0,0 +1 @@
+1.0