/* arm_nrv2e_d8.S -- ARM decompressor for NRV2E

   This file is part of the UPX executable compressor.

   Copyright (C) Markus Franz Xaver Johannes Oberhumer
   Copyright (C) Laszlo Molnar
   Copyright (C) John F. Reiser
   All Rights Reserved.

   UPX and the UCL library are free software; you can redistribute them
   and/or modify them under the terms of the GNU General Public License as
   published by the Free Software Foundation; either version 2 of
   the License, or (at your option) any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; see the file COPYING.
   If not, write to the Free Software Foundation, Inc.,
   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

   Markus F.X.J. Oberhumer              Laszlo Molnar
   <markus@oberhumer.com>               <ezerotven+github@gmail.com>

   John F. Reiser
   <jreiser@users.sourceforge.net>
*/
#define SAFE 0  /* 1 for src+dst bounds checking: cost 40 bytes */

src  .req r0
len  .req r1  /* overlaps 'cnt' */
dst  .req r2
tmp  .req r3
bits .req r4
off  .req r5
wrnk .req r6  /* 0x500  M2_MAX_OFFSET before "wrinkle" */
srclim .req r7
#if 1==SAFE  /*{*/
dstlim .req r12
#endif  /*}*/

cnt  .req r1  /* overlaps 'len' while reading an offset */

#if 1==SAFE  /*{*/
#define CHECK_SRC  cmp src,srclim; bhs bad_src_n2e
#define CHECK_DST  cmp dst,dstlim; bhs bad_dst_n2e
#else  /*}{*/
#define CHECK_SRC  /*empty*/
#define CHECK_DST  /*empty*/
#endif  /*}*/

#if 0  /*{ DEBUG only: check newly-decompressed against original dst */
#define CHECK_BYTE \
   push {wrnk}; \
   ldrb  wrnk,[dst]; \
   cmp   wrnk,tmp; beq 0f; bkpt; \
0: pop  {wrnk}
#else  /*}{*/
#define CHECK_BYTE  /*empty*/
#endif  /*}*/

/* "mov lr,pc; bxx ..." implements conditional subroutine call */
#define GETBIT  add bits,bits; mov lr,pc; beq get1_n2e

#define getnextb(reg) GETBIT; adc reg,reg
#define   jnextb0     GETBIT; bcc
#define   jnextb1     GETBIT; bcs

#ifndef PURE_THUMB
ucl_nrv2e_decompress_8: .globl ucl_nrv2e_decompress_8  @ ARM mode
        .type ucl_nrv2e_decompress_8, %function
/* error = (*)(char const *src, int len_src, char *dst, int *plen_dst)
   Actual decompressed length is stored through plen_dst.
   For SAFE mode: at call, *plen_dst must be allowed length of output buffer.
*/
        adr r12,1+.thumb_nrv2e_d8; bx r12  @ enter THUMB mode
        .code 16  @ THUMB mode
        .thumb_func
#endif

.thumb_nrv2e_d8:
        push {r2,r3, r4,r5,r6,r7, lr}
#define sp_DST0 0  /* stack offset of original dst */
        add srclim,len,src  @ srclim= eof_src;
#if 1==SAFE  /*{*/
        ldr tmp,[r3]  @ len_dst
        add tmp,dst
        mov dstlim,tmp
#endif  /*}*/
        mov bits,#1; neg off,bits  @ off= -1 initial condition
        lsl bits,#31  @ 1<<31: refill next time
        mov wrnk,#5
        lsl wrnk,#8  @ 0x500  @ nrv2e M2_MAX_OFFSET
        b top_n2e

#if 1==SAFE  /*{*/
bad_dst_n2e:  # return value will be 2
        add src,srclim,#1
bad_src_n2e:  # return value will be 1
        add src,#1
#endif  /*}*/
eof_n2e:
        pop {r3,r4}  @ r3= orig_dst; r4= plen_dst
        sub src,srclim  @ 0 if actual src length equals expected length
        sub dst,r3  @ actual dst length
        str dst,[r4]
        pop {r4,r5,r6,r7 /*,pc*/}
        pop {r1}; bx r1  @ "pop {,pc}" fails return to ARM mode on ARMv4T

get1_n2e:  @ In: Carry set [from adding 0x80000000 (1<<31) to itself]
          ldrb bits,[src]  @ zero-extend next byte
        adc bits,bits  @ double and insert CarryIn as low bit
          CHECK_SRC
          add src,#1
        lsl bits,#24  @ move to top byte, and set CarryOut from old bit 8
        mov pc,lr  @ return, stay in current (THUMB) mode

lit_n2e:
        CHECK_SRC; ldrb tmp,[src]; add src,#1
        CHECK_BYTE
        CHECK_DST; strb tmp,[dst]; add dst,#1
top_n2e:
        jnextb1 lit_n2e
        mov cnt,#1; b getoff_n2e

off_n2e:
        sub cnt,#1
        getnextb(cnt)
getoff_n2e:
        getnextb(cnt)
        jnextb0 off_n2e

        sub tmp,cnt,#3  @ set Carry
        mov len,#0  @ Carry unaffected
        blo offprev_n2e  @ cnt was 2; tests Carry only
        lsl tmp,#8
        CHECK_SRC; ldrb off,[src]; add src,#1  @ low 7+1 bits
        orr  off,tmp
        mvn  off,off; beq eof_n2e  @ off= ~off
        asr  off,#1; bcs lenlast_n2e
        b lenmore_n2e

offprev_n2e:
        jnextb1 lenlast_n2e
lenmore_n2e:
        mov len,#1
        jnextb1 lenlast_n2e
len_n2e:
        getnextb(len)
        jnextb0 len_n2e
        add len,#6-2
        b gotlen_n2e

lenlast_n2e:
        getnextb(len)  @ 0,1,2,3
        add len,#2
gotlen_n2e:  @ 'cmn': add the inputs, set condition codes, discard the sum
        cmn wrnk,off; bcs near_n2e  @ within M2_MAX_OFFSET
        add len,#1  @ too far away, so minimum match length is 3
near_n2e:
#if 1==SAFE  /*{*/
        ldr tmp,[sp,#sp_DST0]
        sub tmp,dst
        sub tmp,off; bhi bad_dst_n2e  @ reaching back too far

        add tmp,dst,cnt
        cmp tmp,dstlim; bhi bad_dst_n2e  @ too much output
#endif  /*}*/
        ldrb tmp,[dst]  @ force cacheline allocate
copy_n2e:
        ldrb tmp,[dst,off]
        CHECK_BYTE
        strb tmp,[dst]; add dst,#1
        sub len,#1; bne copy_n2e
        b top_n2e

#ifndef PURE_THUMB
        .size ucl_nrv2e_decompress_8, .-ucl_nrv2e_decompress_8
#endif

    .unreq src
    .unreq len
    .unreq dst
    .unreq tmp
    .unreq bits
    .unreq off
    .unreq wrnk
    .unreq srclim

/*
vi:ts=8:et:nowrap
 */

