tools/mpy-tool.py: Support freezing float literals with obj-repr C.

The tool now generates code for freezing floats in obj-repr A, B or C,
with the specific representation detected at compile time using macros.

tools/mpy-tool.py

@@ -42,6 +42,7 @@ else:
 # end compatibility code
 
 import sys
+import struct
 from collections import namedtuple
 
 sys.path.append('../py')
@@ -315,9 +316,10 @@ class RawCode:
                         '{.neg=%u, .fixed_dig=1, .alloc=%u, .len=%u, .dig=(uint%u_t[]){%s}}};'
                         % (obj_name, neg, ndigs, ndigs, bits_per_dig, digs))
             elif type(obj) is float:
-                # works for REPR A and B only
+                print('#if MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_A || MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_B')
                 print('STATIC const mp_obj_float_t %s = {{&mp_type_float}, %.16g};'
                     % (obj_name, obj))
+                print('#endif')
             else:
                 # TODO
                 raise FreezeError(self, 'freezing of object %r is not implemented' % (obj,))
@@ -328,7 +330,18 @@ class RawCode:
         for qst in self.qstrs:
             print('    (mp_uint_t)MP_OBJ_NEW_QSTR(%s),' % global_qstrs[qst].qstr_id)
         for i in range(len(self.objs)):
-            print('    (mp_uint_t)&const_obj_%s_%u,' % (self.escaped_name, i))
+            if type(self.objs[i]) is float:
+                print('#if MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_A || MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_B')
+                print('    (mp_uint_t)&const_obj_%s_%u,' % (self.escaped_name, i))
+                print('#elif MICROPY_OBJ_REPR == MICROPY_OBJ_REPR_C')
+                n = struct.unpack('<I', struct.pack('<f', self.objs[i]))[0]
+                n = ((n & ~0x3) | 2) + 0x80800000
+                print('    (mp_uint_t)0x%08x,' % (n,))
+                print('#else')
+                print('#error "MICROPY_OBJ_REPR_D not supported with floats in frozen mpy files"')
+                print('#endif')
+            else:
+                print('    (mp_uint_t)&const_obj_%s_%u,' % (self.escaped_name, i))
         for rc in self.raw_codes:
             print('    (mp_uint_t)&raw_code_%s,' % rc.escaped_name)
         print('};')