xref: /titanic_53/usr/src/lib/libdwarf/common/dwarf_leb.c (revision 7fd791373689a6af05e27efec3b1ab556e02aa23)

/*

  Copyright (C) 2000,2004 Silicon Graphics, Inc.  All Rights Reserved.

  This program is free software; you can redistribute it and/or modify it
  under the terms of version 2.1 of the GNU Lesser General Public License
  as published by the Free Software Foundation.

  This program is distributed in the hope that it would be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

  Further, this software is distributed without any warranty that it is
  free of the rightful claim of any third person regarding infringement
  or the like.  Any license provided herein, whether implied or
  otherwise, applies only to this software file.  Patent licenses, if
  any, provided herein do not apply to combinations of this program with
  other software, or any other product whatsoever.

  You should have received a copy of the GNU Lesser General Public
  License along with this program; if not, write the Free Software
  Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston MA 02110-1301,
  USA.

  Contact information:  Silicon Graphics, Inc., 1500 Crittenden Lane,
  Mountain View, CA 94043, or:

  http://www.sgi.com

  For further information regarding this notice, see:

  http://oss.sgi.com/projects/GenInfo/NoticeExplan

*/



#include "config.h"
#include "dwarf_incl.h"
#include <stdio.h>


/*
    decode ULEB
*/
Dwarf_Unsigned
_dwarf_decode_u_leb128(Dwarf_Small * leb128, Dwarf_Word * leb128_length)
{
    unsigned char byte;
    Dwarf_Word word_number;
    Dwarf_Unsigned number;
    Dwarf_Sword shift;
    Dwarf_Sword byte_length;

    /* The following unrolls-the-loop for the first few bytes and
       unpacks into 32 bits to make this as fast as possible.
       word_number is assumed big enough that the shift has a defined
       result. */
    if ((*leb128 & 0x80) == 0) {
        if (leb128_length != NULL)
            *leb128_length = 1;
        return (*leb128);
    } else if ((*(leb128 + 1) & 0x80) == 0) {
        if (leb128_length != NULL)
            *leb128_length = 2;

        word_number = *leb128 & 0x7f;
        word_number |= (*(leb128 + 1) & 0x7f) << 7;
        return (word_number);
    } else if ((*(leb128 + 2) & 0x80) == 0) {
        if (leb128_length != NULL)
            *leb128_length = 3;

        word_number = *leb128 & 0x7f;
        word_number |= (*(leb128 + 1) & 0x7f) << 7;
        word_number |= (*(leb128 + 2) & 0x7f) << 14;
        return (word_number);
    } else if ((*(leb128 + 3) & 0x80) == 0) {
        if (leb128_length != NULL)
            *leb128_length = 4;

        word_number = *leb128 & 0x7f;
        word_number |= (*(leb128 + 1) & 0x7f) << 7;
        word_number |= (*(leb128 + 2) & 0x7f) << 14;
        word_number |= (*(leb128 + 3) & 0x7f) << 21;
        return (word_number);
    }

    /* The rest handles long numbers Because the 'number' may be larger
       than the default int/unsigned, we must cast the 'byte' before
       the shift for the shift to have a defined result. */
    number = 0;
    shift = 0;
    byte_length = 1;
    byte = *(leb128);
    for (;;) {
        number |= ((Dwarf_Unsigned) (byte & 0x7f)) << shift;

        if ((byte & 0x80) == 0) {
            if (leb128_length != NULL)
                *leb128_length = byte_length;
            return (number);
        }
        shift += 7;

        byte_length++;
        ++leb128;
        byte = *leb128;
    }
}

#define BITSINBYTE 8

/*
    decode SLEB
*/
Dwarf_Signed
_dwarf_decode_s_leb128(Dwarf_Small * leb128, Dwarf_Word * leb128_length)
{
    Dwarf_Signed number = 0;
    Dwarf_Bool sign = 0;
    Dwarf_Sword shift = 0;
    unsigned char byte = *leb128;
    Dwarf_Sword byte_length = 1;

    /* byte_length being the number of bytes of data absorbed so far in
       turning the leb into a Dwarf_Signed. */

    for (;;) {
        sign = byte & 0x40;
        number |= ((Dwarf_Signed) ((byte & 0x7f))) << shift;
        shift += 7;

        if ((byte & 0x80) == 0) {
            break;
        }
        ++leb128;
        byte = *leb128;
        byte_length++;
    }

    if ((shift < sizeof(Dwarf_Signed) * BITSINBYTE) && sign) {
        number |= -((Dwarf_Signed) 1 << shift);
    }

    if (leb128_length != NULL)
        *leb128_length = byte_length;
    return (number);
}