[review v6] Add a fast_hash function in common-utils

[Christian Biesinger (Code Review)]

Change URL: https://gnutoolchain-gerrit.osci.io/r/c/binutils-gdb/+/38
......................................................................

Add a fast_hash function in common-utils

Also updates a caller in symtab.c. For now this just calls htab_hash_string
but the next patch will change it to xxhash, if available.

gdb/ChangeLog:

2019-10-22  Christian Biesinger  <cbiesinger@google.com>

	* utils.h (fast_hash): New function.
	* symtab.c (hash_demangled_name_entry): Call new function
	fast_hash.

Change-Id: I77cac0d9aa78fc65316a2af449f52edcae72dc9b
---
M gdb/ChangeLog
M gdb/symtab.c
M gdb/utils.h
3 files changed, 18 insertions(+), 1 deletion(-)



diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index d271330..bbf5d08 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,11 @@
 2019-10-22  Christian Biesinger  <cbiesinger@google.com>
 
+	* utils.h (fast_hash): New function.
+	* symtab.c (hash_demangled_name_entry): Call new function
+	fast_hash.
+
+2019-10-22  Christian Biesinger  <cbiesinger@google.com>
+
 	* symtab.c (struct demangled_name_entry): Change type of mangled
 	to gdb::string_view. Also adds a constructor that takes the
 	mangled name.
diff --git a/gdb/symtab.c b/gdb/symtab.c
index 567d09d..dff92ca 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -70,6 +70,7 @@
 #include <algorithm>
 #include "gdbsupport/gdb_string_view.h"
 #include "gdbsupport/pathstuff.h"
+#include "gdbsupport/common-utils.h"
 
 /* Forward declarations for local functions.  */
 
@@ -727,7 +728,7 @@
   const struct demangled_name_entry *e
     = (const struct demangled_name_entry *) data;
 
-  return iterative_hash (e->mangled.data (), e->mangled.length (), 0);
+  return fast_hash (e->mangled.data (), e->mangled.length ());
 }
 
 /* Equality function for the demangled name hash.  */
diff --git a/gdb/utils.h b/gdb/utils.h
index af8b461..478c485 100644
--- a/gdb/utils.h
+++ b/gdb/utils.h
@@ -567,4 +567,14 @@
 			  const gdb_byte *source, ULONGEST source_offset,
 			  ULONGEST nbits, int bits_big_endian);
 
+/* A fast hashing function.  This can be used to hash strings in a fast way
+   when the length is known.  If no fast hashing library is available, falls
+   back to iterative_hash from libiberty.  */
+
+static inline unsigned int
+fast_hash (const char* str, size_t len)
+{
+  return iterative_hash (str, len, 0);
+}
+
 #endif /* UTILS_H */