py/obj: Fix nan handling in object REPR_C and REPR_D.

CPython math.nan is positive with regards to copysign.  The signaling bit
(aka sign flag) was incorrectly set.

In addition, REPR_C and REPR_D should only use the _true_ nan to prevent
system crash in case of hand-crafted floats.  For instance, with REPR_C,
any nan-like float following the pattern
`01111111 1xxxxxxx xxxxxxxx xxxxx1xx` would be switched to an immediate
object or a qstr string.  When the qstr index is too large, this would
cause a crash.

This commit fixes the issue, and adds the relevant test cases.

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

py/modmath.c

@@ -161,6 +161,11 @@ MATH_FUN_2(atan2, atan2)
 MATH_FUN_1_TO_INT(ceil, ceil)
 // copysign(x, y)
 static mp_float_t MICROPY_FLOAT_C_FUN(copysign_func)(mp_float_t x, mp_float_t y) {
+    #if MICROPY_PY_MATH_COPYSIGN_FIX_NAN
+    if (isnan(y)) {
+        y = 0.0;
+    }
+    #endif
     return MICROPY_FLOAT_C_FUN(copysign)(x, y);
 }
 MATH_FUN_2(copysign, copysign_func)

py/obj.h

@@ -184,13 +184,15 @@ static inline bool mp_obj_is_small_int(mp_const_obj_t o) {
 #define MP_OBJ_NEW_SMALL_INT(small_int) ((mp_obj_t)((((mp_uint_t)(small_int)) << 1) | 1))
 
 #if MICROPY_PY_BUILTINS_FLOAT
-#define MP_OBJ_NEW_CONST_FLOAT(f) MP_ROM_PTR((mp_obj_t)((((((uint64_t)f) & ~3) | 2) + 0x80800000) & 0xffffffff))
+#include <math.h>
+// note: MP_OBJ_NEW_CONST_FLOAT should be a MP_ROM_PTR but that macro isn't available yet
+#define MP_OBJ_NEW_CONST_FLOAT(f) ((mp_obj_t)((((((uint64_t)f) & ~3) | 2) + 0x80800000) & 0xffffffff))
 #define mp_const_float_e  MP_OBJ_NEW_CONST_FLOAT(0x402df854)
 #define mp_const_float_pi MP_OBJ_NEW_CONST_FLOAT(0x40490fdb)
+#define mp_const_float_nan MP_OBJ_NEW_CONST_FLOAT(0x7fc00000)
 #if MICROPY_PY_MATH_CONSTANTS
 #define mp_const_float_tau MP_OBJ_NEW_CONST_FLOAT(0x40c90fdb)
 #define mp_const_float_inf MP_OBJ_NEW_CONST_FLOAT(0x7f800000)
-#define mp_const_float_nan MP_OBJ_NEW_CONST_FLOAT(0xffc00000)
 #endif
 
 static inline bool mp_obj_is_float(mp_const_obj_t o) {
@@ -207,6 +209,10 @@ static inline mp_float_t mp_obj_float_get(mp_const_obj_t o) {
     return num.f;
 }
 static inline mp_obj_t mp_obj_new_float(mp_float_t f) {
+    if (isnan(f)) {
+        // prevent creation of bad nanboxed pointers via array.array or struct
+        return mp_const_float_nan;
+    }
     union {
         mp_float_t f;
         mp_uint_t u;
@@ -257,12 +263,13 @@ static inline bool mp_obj_is_immediate_obj(mp_const_obj_t o) {
 #error MICROPY_OBJ_REPR_D requires MICROPY_FLOAT_IMPL_DOUBLE
 #endif
 
+#include <math.h>
 #define mp_const_float_e {((mp_obj_t)((uint64_t)0x4005bf0a8b145769 + 0x8004000000000000))}
 #define mp_const_float_pi {((mp_obj_t)((uint64_t)0x400921fb54442d18 + 0x8004000000000000))}
+#define mp_const_float_nan {((mp_obj_t)((uint64_t)0x7ff8000000000000 + 0x8004000000000000))}
 #if MICROPY_PY_MATH_CONSTANTS
 #define mp_const_float_tau {((mp_obj_t)((uint64_t)0x401921fb54442d18 + 0x8004000000000000))}
 #define mp_const_float_inf {((mp_obj_t)((uint64_t)0x7ff0000000000000 + 0x8004000000000000))}
-#define mp_const_float_nan {((mp_obj_t)((uint64_t)0xfff8000000000000 + 0x8004000000000000))}
 #endif
 
 static inline bool mp_obj_is_float(mp_const_obj_t o) {
@@ -276,6 +283,13 @@ static inline mp_float_t mp_obj_float_get(mp_const_obj_t o) {
     return num.f;
 }
 static inline mp_obj_t mp_obj_new_float(mp_float_t f) {
+    if (isnan(f)) {
+        // prevent creation of bad nanboxed pointers via array.array or struct
+        struct {
+            uint64_t r;
+        } num = mp_const_float_nan;
+        return num.r;
+    }
     union {
         mp_float_t f;
         uint64_t r;