Fix broken bignum to int_ptr_t conversion.

This one affects all platforms. The extra sign check and
negation cancels out the one done in mp_get_uintptr, causing a
positive value for a negative input value.

* mpi/mpi.c (mp_get_intptr): Just coerce the uint_ptr_t
result to int_ptr_t.  That has the right semantics under
that the bits are preserved (under two's complement, in every
compiler I've ever used).  The unsigned value from
mp_get_uintptr already looks like the image of a two's
complement value.

1 files changed, 2 insertions, 3 deletions

diff --git a/mpi/mpi.c b/mpi/mpi.c
index 96dc71d4..42a267b5 100644
--- a/mpi/mpi.c
+++ b/mpi/mpi.c
@@ -606,10 +606,9 @@ mp_err mp_get_uintptr(mp_int *mp, uint_ptr_t *z)
 mp_err mp_get_intptr(mp_int *mp, int_ptr_t *z)
 {
   uint_ptr_t tmp = 0;
-  int_ptr_t out;
   mp_get_uintptr(mp, &tmp);
-  out = tmp;
-  *z = (SIGN(mp) == MP_NEG) ? -out : out;
+  /* Reliance on bitwise unsigned to two's complement conversion */
+  *z = (int_ptr_t) tmp;
   return MP_OKAY;
 }