/* arm_nrv2b_d8.S -- ARM decompressor for NRV2B

   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>
*/

src  .req r0
len  .req r1
dst  .req r2
tmp  .req r3
bits .req r4
off  .req r5
/*           r6  UNUSED */
wrnk .req r7  /* 0xd00  M2_MAX_OFFSET before "wrinkle" */

/* r12 ("ip") is assumed to be a scratch register. */

#define GETBIT  add bits,bits; mov lr,pc; beq get1_n2b

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

#ifndef PURE_THUMB
ucl_nrv2b_decompress_8: .globl ucl_nrv2b_decompress_8  @ ARM mode
        .type ucl_nrv2b_decompress_8, %function
/* error = (*)(char const *src, int len_src, char *dst, int *plen_dst) */
        adr r12,1+.thumb_nrv2b_d8  @ load pc-relative address
        bx  r12  @ enter THUMB mode
        .code 16  @ THUMB mode
        .thumb_func
#endif

.thumb_nrv2b_d8:
        add r1,len,src  @ r1= eof_src;
        push {r1,r2,r3, r4,r5,r6,r7, lr}
        mov bits,#1; neg off,bits  @ off= -1 initial condition
        lsl bits,#31  @ 1<<31: refill next time
        mov wrnk,#0xd
        lsl wrnk,#8  @ 0xd00
        b top_n2b

eof_n2b:
        pop {r1,r3,r4}  @ r1= eof_src; r3= orig_dst; r4= plen_dst
        sub src,r1  @ 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_n2b:
        ldrb bits,[src]  @ zero-extend next byte
        adc bits,bits  @ double and insert CarryIn as low bit
        add src,#1
        lsl bits,#24  @ move to top byte, and set CarryOut from old bit 8
        mov pc,lr

lit_n2b:
        ldrb tmp,[src]; add src,#1
        strb tmp,[dst]; add dst,#1
top_n2b:
        jnextb1 lit_n2b
        mov len,#1  @ the msb
getoff_n2b:  @ ss11 len= [2..)
        getnextb(len)
        jnextb0 getoff_n2b

        sub tmp,len,#3  @ set Carry
        mov len,#0  @ Carry unaffected
        blo offprev_n2b  @ ss11 returned 2
        lsl tmp,#8
        ldrb off,[src]; add src,#1  @ low 8 bits
        orr  off,tmp
        mvn  off,off; beq eof_n2b  @ off= ~off
offprev_n2b:  @ In: 0==len
        getnextb(len); getnextb(len); bne plus1_n2b  @ two bits; 1,2,3 ==> 2,3,4

        mov len,#1  @ the msb
getlen_n2b:  @ ss11 len= [2..)
        getnextb(len)
        jnextb0 getlen_n2b

        add len,#2  @ [2..) ==> [4..);
plus1_n2b:
        add len,#1  @ 1,2,3 ==> 2,3,4; [4..) ==> [5..)
/* 'cmn': add the inputs, set condition codes, discard the sum */
        cmn off,wrnk; bcs near_n2b  @ within M2_MAX_OFFSET
        add len,#1  @ too far away, so minimum match length is 3
near_n2b:
        ldrb tmp,[dst]  @ force cacheline allocate
copy_n2b:
        ldrb tmp,[dst,off]
        strb tmp,[dst]; add dst,#1
        sub len,#1; bne copy_n2b
        b top_n2b

#ifndef PURE_THUMB
        .size ucl_nrv2b_decompress_8, .-ucl_nrv2b_decompress_8
#endif

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

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

