py,extmod: Some casts and minor refactors to quiet compiler warnings.
diff --git a/py/objint.c b/py/objint.c
index 0b49041..2749ec5 100644
--- a/py/objint.c
+++ b/py/objint.c
@@ -106,7 +106,7 @@
 #define MP_FLOAT_SIGN_SHIFT_I32 ((MP_FLOAT_FRAC_BITS + MP_FLOAT_EXP_BITS) % 32)
 #define MP_FLOAT_EXP_SHIFT_I32 (MP_FLOAT_FRAC_BITS % 32)
 
-    if (e & (1 << MP_FLOAT_SIGN_SHIFT_I32)) {
+    if (e & (1U << MP_FLOAT_SIGN_SHIFT_I32)) {
 #if MICROPY_FLOAT_IMPL == MICROPY_FLOAT_IMPL_DOUBLE
         e |= u.i[MP_ENDIANNESS_BIG] != 0;
 #endif