[RFA] leb128.h: New file.

[dje at google dot com (Doug Evans)]

Hi.

This patch creates leb128.h which contains a few functions for
reading leb128 values.
They're in a header as static inlines because they can be speed critical.
I've only included what I need in GDB.

Ok to check in?

2012-05-14  Doug Evans  <dje@google.com>

	* leb128.h: New file.

Index: leb128.h
===================================================================
RCS file: leb128.h
diff -N leb128.h
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ leb128.h	15 May 2012 04:56:33 -0000
@@ -0,0 +1,116 @@
+/* Utilities for reading leb128 values.
+   Copyright (C) 2012 Free Software Foundation, Inc.
+
+This file is part of the libiberty library.
+Libiberty is free software; you can redistribute it and/or
+modify it under the terms of the GNU Library General Public
+License as published by the Free Software Foundation; either
+version 2 of the License, or (at your option) any later version.
+
+Libiberty is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+Library General Public License for more details.
+
+You should have received a copy of the GNU Library General Public
+License along with libiberty; see the file COPYING.LIB.  If not, write
+to the Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
+Boston, MA 02110-1301, USA.  */
+
+/* The functions defined here can be speed critical.
+   Since they are all pretty small we keep things simple and just define
+   them all as "static inline".  */
+
+#ifndef LEB128_H
+#define LEB128_H
+
+#include "ansidecl.h"
+
+/* Get a definition for NULL.  */
+#include <stdio.h>
+
+#ifdef HAVE_STDINT_H
+#include <stdint.h>
+#endif
+#ifdef HAVE_INTTYPES_H
+#include <inttypes.h>
+#endif
+
+/* Decode the unsigned LEB128 constant at BUF into the variable pointed to
+   by R, and return the new value of BUF.
+   If we read off the end of the buffer, NULL is returned.  */
+
+static inline const unsigned char *
+read_uleb128 (const unsigned char *buf, const unsigned char *buf_end,
+	      uint64_t *r)
+{
+  unsigned int shift = 0;
+  uint64_t result = 0;
+  unsigned char byte;
+
+  while (1)
+    {
+      if (buf >= buf_end)
+	return NULL;
+
+      byte = *buf++;
+      result |= ((uint64_t) (byte & 0x7f)) << shift;
+      if ((byte & 0x80) == 0)
+	break;
+      shift += 7;
+    }
+
+  *r = result;
+  return buf;
+}
+
+/* Decode the signed LEB128 constant at BUF into the variable pointed to
+   by R, and return the new value of BUF.
+   If we read off the end of the buffer, NULL is returned.  */
+
+static inline const unsigned char *
+read_sleb128 (const unsigned char *buf, const unsigned char *buf_end,
+	      int64_t *r)
+{
+  unsigned int shift = 0;
+  int64_t result = 0;
+  unsigned char byte;
+
+  while (1)
+    {
+      if (buf >= buf_end)
+	return NULL;
+
+      byte = *buf++;
+      result |= ((uint64_t) (byte & 0x7f)) << shift;
+      shift += 7;
+      if ((byte & 0x80) == 0)
+	break;
+    }
+  if (shift < (sizeof (*r) * 8) && (byte & 0x40) != 0)
+    result |= -(((uint64_t) 1) << shift);
+
+  *r = result;
+  return buf;
+}
+
+/* Return a pointer to just past the end of an LEB128 number in BUF.
+   If the end isn't found before reaching BUF_END, return NULL.  */
+
+static inline const unsigned char *
+skip_leb128 (const unsigned char *buf, const unsigned char *buf_end)
+{
+  unsigned char byte;
+
+  while (1)
+    {
+      if (buf == buf_end)
+	return NULL;
+
+      byte = *buf++;
+      if ((byte & 128) == 0)
+	return buf;
+    }
+}
+
+#endif /* LEB128_H */