/* armv4_n2e_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 76 bytes */

src  .req r0
len  .req r1  /* overlaps 'cnt' */
dst  .req r2
tmp  .req r3
bits .req r4
off  .req r5
/*           r6  UNUSED in ARM code unless DEBUG mode */
srclim .req r7
#if 1==SAFE  /*{*/
#define dstlim r12  /* bug: .req r12 */
#endif  /*}*/

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

/* 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

#if 1==SAFE  /*{*/
#define CHECK_SRC  cmp srclim,src; bls bad_src_n2e /* Out: 1==Carry for get8_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 \
   ldrb  r6,[dst]; \
   cmp   r6,tmp; beq 0f; bkpt; 0:
#else  /*}{*/
#define CHECK_BYTE  /*empty*/
#endif  /*}*/

#undef GETBIT
#define GETBIT  ADD2S(bits,bits); bleq get8_n2e

#undef getnextb
#define getnextb(reg) GETBIT; ADC2(reg,reg) /* Out: condition code not changed */
#define   jnextb0     GETBIT; bcc
#define   jnextb1     GETBIT; bcs

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.
*/
        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 dstlim,tmp,dst
#endif  /*}*/
        mvn off,#~-1  // off= -1 initial condition
        mov bits,#1<<31  // refill next time
        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
        ADD2(src,#1)
#endif  /*}*/
eof_n2e:
        POP {r3,r4}  // r3= orig_dst; r4= plen_dst
        SUB2(src,srclim)  // 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,r6,r7 ,pc}

get8_n2e:  // In: Carry set [from adding 0x80000000 (1<<31) to itself]
        CHECK_SRC; LDRB3(bits,[src],#1)  // zero-extend next byte
        adc  bits,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

lit_n2e:
        CHECK_SRC; LDRB3(tmp,[src],#1)
        CHECK_BYTE
        CHECK_DST; STRB3(tmp,[dst],#1)
top_n2e:
        jnextb1 lit_n2e
        mov cnt,#1; b getoff_n2e

off_n2e:
        SUB2(cnt,#1)
        getnextb(cnt)
getoff_n2e:
        getnextb(cnt)
        jnextb0 off_n2e

        subs tmp,cnt,#3  // set Carry
        mov len,#0  // Carry unaffected
        blo offprev_n2e  // cnt was 2; tests Carry only
        CHECK_SRC; LDRB3(off,[src],#1)  // low 7+1 bits
        orr  off,off,tmp,lsl #8
        mvns off,off; beq eof_n2e  // off= ~off
        movs off,off,asr #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
        ADD2(len,#6-2)
        b gotlen_n2e

lenlast_n2e:
        getnextb(len)  // 0,1,2,3
        ADD2(len,#2)
gotlen_n2e:  // 'cmn': add the inputs, set condition codes, discard the sum
        cmn off,#5<<8  // within M2_MAX_OFFSET
        addcc len,len,#1  // too far away, so minimum match length is 3
near_n2e:
#if 1==SAFE  /*{*/
        ldr tmp,[sp,#sp_DST0]
        SUB2( tmp,dst)
        SUB2S(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  /*}*/
        add tmp,dst,len
        ldrb tmp,[tmp,#-1]  // force cacheline allocate
copy_n2e:
        ldrb tmp,[dst,off]
        CHECK_BYTE
        STRB3(tmp,[dst],#1)
        SUB2S(len,#1); bne copy_n2e
        b top_n2e

        .size ucl_nrv2e_decompress_8, .-ucl_nrv2e_decompress_8

    .unreq src
    .unreq len
    .unreq dst
    .unreq tmp
    .unreq bits
    .unreq off
    .unreq srclim
//    .unreq dstlim
    .unreq cnt
/*
vi:ts=8:et:nowrap
 */
