/* 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

/* macros reduce "noise" when comparing this ARM code to corresponding THUMB code */
#define PUSH stmdb sp!,
#define POP  ldmia sp!,
#define ADD2( dst,src) add  dst,dst,src
#define ADD2S(dst,src) adds dst,dst,src
#define ADC2( dst,src) adc  dst,dst,src
#define ADC2S(dst,src) adcs dst,dst,src
#define SUB2( dst,src) sub  dst,dst,src
#define SUB2S(dst,src) subs dst,dst,src
#define LDRB3(reg,psrc,incr) ldrb reg,psrc,incr
#define STRB3(reg,pdst,incr) strb reg,pdst,incr

#undef  GETBIT
#define GETBIT  bl get1_n2b

#define getnextb(reg) GETBIT; ADC2S(reg,reg) /* Set Condition Codes on result */
#define   jnextb0     GETBIT; bcc
#define   jnextb1     GETBIT; bcs

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) */
        add r1,len,src  // r1= eof_src;
        PUSH {r1,r2,r3, r4,r5, lr}
        mvn off,#~-1  // off= -1 initial condition
        mov bits,#1<<31  // refill next time
        b top_n2b

eof_n2b:
        POP {r1,r3,r4}  // r1= eof_src; r3= orig_dst; r4= plen_dst
        SUB2(src,r1)  // 0 if actual src length equals expected length
        SUB2(dst,r3)  // actual dst length
        str dst,[r4]

#if defined(LINUX_ARM_CACHEFLUSH)  /*{*/
        mov r4,r0  // save result value
        mov r0,r3  // orig_dst
        add r1,r3,dst  // orig_dst + dst_len
        mov r2,#0
        do_sys2 __ARM_NR_cacheflush  // decompressed region
        mov r0,r4  // result value
#endif  /*}*/
#if defined(DARWIN_ARM_CACHEFLUSH)  /*{*/
        mov r4,r0  // save result value
        mov r0,r3  // orig_dst
        mov r1,dst  // dst_len
        PUSH {r0,r1}; do_dcache_flush
        POP  {r0,r1}; do_icache_invalidate
        mov r0,r4  // result value
#endif  /*}*/

        POP {r4,r5, pc}  // return

get1_n2b:
        ADD2S(bits,bits)  // shift left 1 bit, set condition codes
        movne pc,lr  // conditionally return CarryOut if rest is non-empty
get8_n2b:  // In: Carry set [from adding 0x80000000 (1<<31) to itself]
        LDRB3(bits,[src],#1)  // zero-extend next byte
        ADC2(bits,bits)  // double and insert CarryIn as low bit
        movs bits,bits,lsl #24  // move to top byte, and set CarryOut from old bit 8
        mov pc,lr

ss11_n2b:  // return len= [2..)
        mov len,#1  // the msb
        mov ip,lr  // outer ret.addr
1:
        getnextb(len)
        jnextb0 1b
        mov pc,ip  // outer ret

lit_n2b:
        LDRB3(tmp,[src],#1)
        STRB3(tmp,[dst],#1)
top_n2b:
        jnextb1 lit_n2b

        bl ss11_n2b  // len= [2..)
        subs tmp,len,#3  // set Carry
        mov len,#0  // Carry unaffected
        blo offprev_n2b  // ss11 returned 2
        LDRB3(off,[src],#1)  // low 8 bits
        orr  off,off,tmp,lsl #8
        mvns off,off; beq eof_n2b  // off= ~off
offprev_n2b:  // In: 0==len
        getnextb(len); getnextb(len); bne 1f  // two bits; 1,2,3 ==> 2,3,4
        bl ss11_n2b  // len= [2..)
        ADD2(len,#2)  // [2..) ==> [4..);
1:
/* 'cmn': add the inputs, set condition codes, discard the sum */
        cmn off,#0xd<<8  // within M2_MAX_OFFSET
        addcc len,len,#1  // too far away, so minimum match length is 3
copy_n2b:  // copy 1+len bytes
        ldrb  tmp,[dst,off]; SUB2S(len,#1)
        STRB3(tmp,[dst],#1); bhs copy_n2b
        b top_n2b  // exit with -1==len

        .size ucl_nrv2b_decompress_8, .-ucl_nrv2b_decompress_8
.unreq src
.unreq len
.unreq dst
.unreq tmp
.unreq bits
.unreq off
/*
vi:ts=8:et:nowrap
 */
