/*
  Copyright (C) 2000,2004 Silicon Graphics, Inc.  All Rights Reserved.
  Portions Copyright 2011-2020 David Anderson. 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.

*/


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

/*  Note that with 'make check')
    many of the test items
    only make sense if Dwarf_Unsigned (and Dwarf_Signed)
    are 64 bits.  The encode/decode logic should
    be fine whether those types are 64 or 32 bits.
    See runtests.sh */

/*  10 bytes of leb, 7 bits each part of the number, gives
    room for a 64bit number.
    While any number of leading zeroes would be legal, so
    no max is really truly required here, why would a
    compiler generate leading zeros (for unsigned leb)?
    That would seem strange except in rare circumstances
    a compiler may want, for overall alignment, to
    add extra bytes..

    So we allow more than 10 as it is legal for a compiler to
    generate an leb with correct but useless trailing
    zero bytes (note the interaction with sign in the signed case).
    The value of BYTESLEBMAX is arbitrary but allows catching
    corrupt data before dark.
    Before April 2021 BYTESLEBMAX was 10.
*/
#define BYTESLEBMAX 24
#define BITSPERBYTE 8

#define TRUE 1
#define FALSE 0


/* Decode ULEB with checking */
int
_dwarf_decode_u_leb128_chk(Dwarf_Small * leb128,
    Dwarf_Unsigned * leb128_length,
    Dwarf_Unsigned *outval,
    Dwarf_Byte_Ptr endptr)
{
    unsigned       byte        = 0;
    Dwarf_Unsigned word_number = 0;
    Dwarf_Unsigned number      = 0;
    size_t shift               = 0;
    /*  The byte_length value will be a small non-negative integer. */
    unsigned byte_length       = 0;

    if (leb128 >=endptr) {
        return DW_DLV_ERROR;
    }
    /*  The following unrolls-the-loop for the first two 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. */
    byte = *leb128;
    if ((byte & 0x80) == 0) {
        if (leb128_length) {
            *leb128_length = 1;
        }
        *outval = byte;
        return DW_DLV_OK;
    } else {
        unsigned       byte2        = 0;
        if ((leb128+1) >=endptr) {
            return DW_DLV_ERROR;
        }
        byte2 = *(leb128 + 1);
        if ((byte2 & 0x80) == 0) {
            if (leb128_length) {
                *leb128_length = 2;
            }
            word_number = byte & 0x7f;
            word_number |= (byte2 & 0x7f) << 7;
            *outval = word_number;
            return DW_DLV_OK;
        }
        /* Gets messy to hand-inline more byte checking. */
    }

    /*  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;
    for (;;) {
        unsigned b = byte & 0x7f;
        if (shift >= (sizeof(number)*BITSPERBYTE)) {
            /*  Shift is large. Maybe corrupt value,
                maybe some padding high-end byte zeroes
                that we can ignore. */
            if (!b) {
                ++byte_length;
                if (byte_length > BYTESLEBMAX) {
                    /*  Erroneous input.  */
                    if (leb128_length) {
                        *leb128_length = BYTESLEBMAX;
                    }
                    return DW_DLV_ERROR;
                }
                ++leb128;
                /*  shift cannot overflow as
                    BYTESLEBMAX is not a large value */
                shift += 7;
                if (leb128 >=endptr) {
                    return DW_DLV_ERROR;
                }
                byte = *leb128;
                continue;
            }
            /*  Too big, corrupt data given the non-zero
                byte content */
            return DW_DLV_ERROR;
        }
        number |= ((Dwarf_Unsigned)b << shift);
        if ((byte & 0x80) == 0) {
            if (leb128_length) {
                *leb128_length = byte_length;
            }
            *outval = number;
            return DW_DLV_OK;
        }
        shift += 7;
        byte_length++;
        if (byte_length > BYTESLEBMAX) {
            /*  Erroneous input.  */
            if (leb128_length) {
                *leb128_length = BYTESLEBMAX;
            }
            break;
        }
        ++leb128;
        if (leb128 >=endptr) {
            return DW_DLV_ERROR;
        }
        byte = *leb128;
    }
    return DW_DLV_ERROR;
}
/* Public Interface: Decode an unsigned LEB128 value. */
int
dwarf_decode_leb128(char* leb, Dwarf_Unsigned* leblen,
    Dwarf_Unsigned* outval, char* endptr)
{
    return _dwarf_decode_u_leb128_chk((Dwarf_Small*)leb,
        leblen, outval,
        (Dwarf_Small*)endptr);
}

int
_dwarf_decode_s_leb128_chk(Dwarf_Small * leb128,
    Dwarf_Unsigned * leb128_length,
    Dwarf_Signed *outval,Dwarf_Byte_Ptr endptr)
{
    Dwarf_Unsigned byte  = 0;
    unsigned int b       = 0;
    Dwarf_Signed number  = 0;
    size_t shift         = 0;
    int    sign          = FALSE;
    /*  The byte_length value will be a small non-negative integer. */
    unsigned byte_length = 1;

    /*  byte_length being the number of bytes
        of data absorbed so far in
        turning the leb into a Dwarf_Signed. */
    if (!outval) {
        return DW_DLV_ERROR;
    }
    if (leb128 >= endptr) {
        return DW_DLV_ERROR;
    }
    byte   = *leb128;
    for (;;) {
        b = byte & 0x7f;
        if (shift >= (sizeof(number)*BITSPERBYTE)) {
            /*  Shift is large. Maybe corrupt value,
                maybe some padding high-end byte zeroes
                that we can ignore (but notice sign bit
                from the last usable byte). */

            sign =  b & 0x40;
            if (!byte || byte == 0x40) {
                /*  The value is complete. */
                break;
            }
            if (b == 0) {
                ++byte_length;
                if (byte_length > BYTESLEBMAX) {
                    /*  Erroneous input.  */
                    if (leb128_length) {
                        *leb128_length = BYTESLEBMAX;
                    }
                    return DW_DLV_ERROR;
                }
                ++leb128;
                /*  shift cannot overflow as
                    BYTESLEBMAX is not a large value */
                shift += 7;
                if (leb128 >=endptr) {
                    return DW_DLV_ERROR;
                }
                byte = *leb128;
                continue;
            }
            /*  Too big, corrupt data given the non-zero
                byte content */
            return DW_DLV_ERROR;
        }
        /*  This bit of the last (most-significant
            useful) byte indicates sign */
        sign =  b & 0x40;
        number |= ((Dwarf_Unsigned)b) << shift;
        shift += 7;
        if ((byte & 0x80) == 0) {
            break;
        }
        ++leb128;
        if (leb128 >= endptr) {
            return DW_DLV_ERROR;
        }
        byte = *leb128;
        byte_length++;
        if (byte_length > BYTESLEBMAX) {
            /*  Erroneous input. */
            if (leb128_length) {
                *leb128_length = BYTESLEBMAX;
            }
            return DW_DLV_ERROR;
        }
    }
    if (sign) {
        /* The following avoids undefined behavior. */
        unsigned shiftlim = sizeof(Dwarf_Signed) * BITSPERBYTE -1;
        if (shift < shiftlim) {
            Dwarf_Signed y = (Dwarf_Signed)
                (((Dwarf_Unsigned)1) << shift);
            Dwarf_Signed x = -y;
            number |= x;
        } else if (shift == shiftlim) {
            Dwarf_Signed x= (((Dwarf_Unsigned)1) << shift);
            number |= x;
        } else {
            /* trailing zeroes case */
            Dwarf_Signed x= (((Dwarf_Unsigned)1) << shiftlim);
            number |= x;
        }
    }
    if (leb128_length) {
        *leb128_length = byte_length;
    }
    *outval = number;
    return DW_DLV_OK;
}


/* Public Interface: Decode a signed LEB128 value. */
int
dwarf_decode_signed_leb128(char* leb, Dwarf_Unsigned* leblen,
    Dwarf_Signed* outval, char* endptr)
{
    return _dwarf_decode_s_leb128_chk((Dwarf_Small *)leb,
        leblen, outval,
        (Dwarf_Small*)endptr);
}