Be more careful about pointers to bignum vals

This uses ‘const’ to be better at catching bugs that
mistakenly attempt to modify a bignum value.
Lisp bignums are supposed to be immutable.
* src/alloc.c (make_pure_bignum):
* src/fns.c (sxhash_bignum):
Accept Lisp_Object instead of struct Lisp_Bignum *, as that’s
simpler now.  Caller changed.
* src/bignum.h (bignum_val, xbignum_val): New inline functions.
Prefer them to &i->value and XBIGNUM (i)->value, since they
apply ‘const’ to the result.
* src/timefns.c (lisp_to_timespec): Use mpz_t const *
to point to a bignum value.

1 files changed, 15 insertions, 2 deletions

diff --git a/src/bignum.h b/src/bignum.h
index 9a32ffb0374..bf7b3669537 100644
--- a/src/bignum.h
+++ b/src/bignum.h
@@ -80,6 +80,19 @@ mpz_set_uintmax (mpz_t result, uintmax_t v)
     mpz_set_uintmax_slow (result, v);
 }
 
+/* Return a pointer to the mpz_t value represented by the bignum I.
+   It is const because the value should not change.  */
+INLINE mpz_t const *
+bignum_val (struct Lisp_Bignum const *i)
+{
+  return &i->value;
+}
+INLINE mpz_t const *
+xbignum_val (Lisp_Object i)
+{
+  return bignum_val (XBIGNUM (i));
+}
+
 /* Return a pointer to an mpz_t that is equal to the Lisp integer I.
    If I is a bignum this returns a pointer to I's representation;
    otherwise this sets *TMP to I's value and returns TMP.  */
@@ -91,7 +104,7 @@ bignum_integer (mpz_t *tmp, Lisp_Object i)
       mpz_set_intmax (*tmp, XFIXNUM (i));
       return tmp;
     }
-  return &XBIGNUM (i)->value;
+  return xbignum_val (i);
 }
 
 /* Set RESULT to the value stored in the Lisp integer I.  If I is a
@@ -103,7 +116,7 @@ mpz_set_integer (mpz_t result, Lisp_Object i)
   if (FIXNUMP (i))
     mpz_set_intmax (result, XFIXNUM (i));
   else
-    mpz_set (result, XBIGNUM (i)->value);
+    mpz_set (result, *xbignum_val (i));
 }
 
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