Re: [RFA] leb128.h: New file.

[dje at google dot com (Doug Evans)]

Hi.

This is a slightly modified version of my previous patch.

ref: http://gcc.gnu.org/ml/gcc-patches/2012-05/msg00962.html

The only change is to make the result of the functions an int
instead of a const pointer.
This lets them be used in places where the code is using
non-const pointers without having to apply ugly casts.

Ok to check in?

2012-05-17  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	17 May 2012 18:23:29 -0000
@@ -0,0 +1,130 @@
+/* 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 number of bytes read.
+   If we read off the end of the buffer, zero is returned,
+   and nothing is stored in R.
+
+   Note: The result is an int instead of a pointer to the next byte to be
+   read to avoid const-vs-non-const problems.  */
+
+static inline int
+read_uleb128 (const unsigned char *buf, const unsigned char *buf_end,
+	      uint64_t *r)
+{
+  const unsigned char *p = buf;
+  unsigned int shift = 0;
+  uint64_t result = 0;
+  unsigned char byte;
+
+  while (1)
+    {
+      if (p >= buf_end)
+	return 0;
+
+      byte = *p++;
+      result |= ((uint64_t) (byte & 0x7f)) << shift;
+      if ((byte & 0x80) == 0)
+	break;
+      shift += 7;
+    }
+
+  *r = result;
+  return p - buf;
+}
+
+/* Decode the signed LEB128 constant at BUF into the variable pointed to
+   by R, and return the number of bytes read.
+   If we read off the end of the buffer, zero is returned,
+   and nothing is stored in R.
+
+   Note: The result is an int instead of a pointer to the next byte to be
+   read to avoid const-vs-non-const problems.  */
+
+static inline int
+read_sleb128 (const unsigned char *buf, const unsigned char *buf_end,
+	      int64_t *r)
+{
+  const unsigned char *p = buf;
+  unsigned int shift = 0;
+  int64_t result = 0;
+  unsigned char byte;
+
+  while (1)
+    {
+      if (p >= buf_end)
+	return 0;
+
+      byte = *p++;
+      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 p - buf;
+}
+
+/* Return the number of bytes to read to skip past an LEB128 number in BUF.
+   If the end isn't found before reaching BUF_END, return zero.
+
+   Note: The result is an int instead of a pointer to the next byte to be
+   read to avoid const-vs-non-const problems.  */
+
+static inline int
+skip_leb128 (const unsigned char *buf, const unsigned char *buf_end)
+{
+  const unsigned char *p = buf;
+  unsigned char byte;
+
+  while (1)
+    {
+      if (p == buf_end)
+	return 0;
+
+      byte = *p++;
+      if ((byte & 128) == 0)
+	return p - buf;
+    }
+}
+
+#endif /* LEB128_H */