py: Add object repr "C", where 30-bit floats are stuffed in obj word.

This new object representation puts floats into the object word instead
of on the heap, at the expense of reducing their precision to 30 bits.
It only makes sense when the word size is 32-bits.

1 files changed, 10 insertions, 0 deletions

diff --git a/py/mpconfig.h b/py/mpconfig.h
index 7ab179304..98e9406c6 100644
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -63,6 +63,16 @@
 //  - xxxx...xxx0 : a pointer to an mp_obj_base_t (unless a fake object)
 #define MICROPY_OBJ_REPR_B (1)
 
+// A MicroPython object is a machine word having the following form:
+//  - iiiiiiii iiiiiiii iiiiiiii iiiiiii1 small int with 31-bit signed value
+//  - x1111111 1qqqqqqq qqqqqqqq qqqqq110 str with 20-bit qstr value
+//  - s1111111 10000000 00000000 00000010 +/- inf
+//  - s1111111 1xxxxxxx xxxxxxxx xxxxx010 nan, x != 0
+//  - seeeeeee efffffff ffffffff ffffff10 30-bit fp, e != 0xff
+//  - pppppppp pppppppp pppppppp pppppp00 ptr (4 byte alignment)
+// This scheme only works with 32-bit word size and float enabled.
+#define MICROPY_OBJ_REPR_C (2)
+
 #ifndef MICROPY_OBJ_REPR
 #define MICROPY_OBJ_REPR (MICROPY_OBJ_REPR_A)
 #endif