py/objfloat: Fix undefined integer behavior hashing negative zero.

Under ubsan, when evaluating hash(-0.) the following diagnostic occurs:

    ../../py/objfloat.c:102:15: runtime error: negation of
    -9223372036854775808 cannot be represented in type 'mp_int_t' (aka
    'long'); cast to an unsigned type to negate this value to itself

So do just that, to tell the compiler that we want to perform this
operation using modulo arithmetic rules.

1 files changed, 1 insertions, 1 deletions

diff --git a/py/objfloat.c b/py/objfloat.c
index 31c624778..b62fe8e71 100644
--- a/py/objfloat.c
+++ b/py/objfloat.c
@@ -99,7 +99,7 @@ typedef uint32_t mp_float_uint_t;
     }
 
     if (u.p.sgn) {
-        val = -val;
+        val = -(mp_uint_t)val;
     }
 
     return val;