gdbsupport: move fast_hash to gdbsupport/common-utils.h

The following patch adds a hash type for gdb::string_view in gdbsupport,
which will use the fast_hash function.  Move the latter to gdbsupport.

Change-Id: Id74510e17801e775bd5ffa5f443713d79adf14ad
Approved-By: Andrew Burgess <aburgess@redhat.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/gdbsupport/common-utils.h b/gdbsupport/common-utils.h
index 530817fff10..31ab1a6cec8 100644
--- a/gdbsupport/common-utils.h
+++ b/gdbsupport/common-utils.h
@@ -27,6 +27,12 @@
 #include "poison.h"
 #include "gdb_string_view.h"
 
+#if defined HAVE_LIBXXHASH
+#  include <xxhash.h>
+#else
+#  include "hashtab.h"
+#endif
+
 /* xmalloc(), xrealloc() and xcalloc() have already been declared in
    "libiberty.h". */
 
@@ -188,4 +194,19 @@ extern int hex2bin (const char *hex, gdb_byte *bin, int count);
 /* Like the above, but return a gdb::byte_vector.  */
 gdb::byte_vector hex2bin (const char *hex);
 
+/* A fast hashing function.  This can be used to hash data in a fast way
+   when the length is known.  If no fast hashing library is available, falls
+   back to iterative_hash from libiberty.  START_VALUE can be set to
+   continue hashing from a previous value.  */
+
+static inline unsigned int
+fast_hash (const void *ptr, size_t len, unsigned int start_value = 0)
+{
+#if defined HAVE_LIBXXHASH
+  return XXH64 (ptr, len, start_value);
+#else
+  return iterative_hash (ptr, len, start_value);
+#endif
+}
+
 #endif /* COMMON_COMMON_UTILS_H */