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

[Doug Evans <dje@google.com>]

Ping.

On Thu, May 17, 2012 at 11:29 AM, Doug Evans <dje@google.com> wrote:
> 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 */