GnuTLS integer-overflow and style fixes

This tweaks the recently-added GnuTLS improvements so that
they avoid some integer-overflow problems and follow typical
Emacs style a bit better.
* configure.ac (HAVE_GNUTLS3_HMAC, HAVE_GNUTLS3_AEAD)
(HAVE_GNUTLS3_CIPHER): Use AC_CACHE_CHECK so that the
configure-time results are displayed.
* src/fns.c (extract_data_from_object): Return char *, not char
const *, since one gnutls caller wants a non-const pointer.  Use
CONSP rather than !NILP when testing for conses.  Use CAR_SAFE
instead of rolling our own code.  Prefer signed types to unsigned
when either will do.  Report problems for lengths out of range,
instead of silently mishandling them.
* src/gnutls.c (emacs_gnutls_strerror): New function, to simplify
callers.  All callers of gnutls_sterror changed.
(Fgnutls_boot): Check for integers out of range rather than
silently truncating them.
(gnutls_symmetric_aead): Check for integer overflow in size
calculations.
(gnutls_symmetric_aead, Fgnutls_macs, Fgnutls_digests):
Prefer signed to unsigned integers where either	will do.
(gnutls_symmetric_aead, gnutls_symmetric):
Work even if ptrdiff_t is wider than ‘long’.
(gnutls_symmetric, Fgnutls_hash_mac, Fgnutls_hash_digest):
Check for integer overflow in algorithm selection.

1 files changed, 1 insertions, 3 deletions

diff --git a/src/lisp.h b/src/lisp.h
index a5134a9532c..9464bf8559f 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3386,9 +3386,7 @@ enum { NEXT_ALMOST_PRIME_LIMIT = 11 };
 extern EMACS_INT next_almost_prime (EMACS_INT) ATTRIBUTE_CONST;
 extern Lisp_Object larger_vector (Lisp_Object, ptrdiff_t, ptrdiff_t);
 extern void sweep_weak_hash_tables (void);
-extern const char* extract_data_from_object (Lisp_Object spec,
-                                             ptrdiff_t *start_byte,
-                                             ptrdiff_t *end_byte);
+extern char *extract_data_from_object (Lisp_Object, ptrdiff_t *, ptrdiff_t *);
 EMACS_UINT hash_string (char const *, ptrdiff_t);
 EMACS_UINT sxhash (Lisp_Object, int);
 Lisp_Object make_hash_table (struct hash_table_test, EMACS_INT, float, float,