Additions to gdb_mpz

In preparation for adding more 128-bit support to gdb, a few additions
to gdb_mpz are needed.

First, this adds a new 'as_integer_truncate' method.  This method
works like 'as_integer' but does not require the value to fit in the
target type -- it just truncates.

Second, gdb_mpz::export_bits is changed to handle the somewhat unusual
situation of zero-length types.  This can happen for a Rust '()' type;
but I think other languages have zero-bit integer types as well.

Finally, this adds some operator== overloads.

1 files changed, 6 insertions, 4 deletions

diff --git a/gdb/gmp-utils.c b/gdb/gmp-utils.c
index 0afa344..13fa61d 100644
--- a/gdb/gmp-utils.c
+++ b/gdb/gmp-utils.c
@@ -69,19 +69,21 @@ void
 gdb_mpz::export_bits (gdb::array_view<gdb_byte> buf, int endian, bool unsigned_p,
 		      bool safe) const
 {
-  gdb_assert (buf.size () > 0);
-
   int sign = mpz_sgn (m_val);
   if (sign == 0)
     {
       /* Our value is zero, so no need to call mpz_export to do the work,
 	 especially since mpz_export's documentation explicitly says
 	 that the function is a noop in this case.  Just write zero to
-	 BUF ourselves.  */
-      memset (buf.data (), 0, buf.size ());
+	 BUF ourselves, if it is non-empty.  In some languages, a
+	 zero-bit type can exist and this is also fine.  */
+      if (buf.size () > 0)
+	memset (buf.data (), 0, buf.size ());
       return;
     }
 
+  gdb_assert (buf.size () > 0);
+
   if (safe)
     {
       /* Determine the maximum range of values that our buffer can