cscg22-gearboy

CSCG 2022 Challenge 'Gearboy'
git clone https://git.sinitax.com/sinitax/cscg22-gearboy
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__strreverse.s (2032B)


      1;--------------------------------------------------------------------------
      2;  __strreverse.s
      3;
      4;  Copyright (C) 2020, Sergey Belyashov
      5;
      6;  This library is free software; you can redistribute it and/or modify it
      7;  under the terms of the GNU General Public License as published by the
      8;  Free Software Foundation; either version 2, or (at your option) any
      9;  later version.
     10;
     11;  This library is distributed in the hope that it will be useful,
     12;  but WITHOUT ANY WARRANTY; without even the implied warranty of
     13;  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
     14;  GNU General Public License for more details.
     15;
     16;  You should have received a copy of the GNU General Public License 
     17;  along with this library; see the file COPYING. If not, write to the
     18;  Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
     19;   MA 02110-1301, USA.
     20;
     21;  As a special exception, if you link this library with other files,
     22;  some of which are compiled with SDCC, to produce an executable,
     23;  this library does not by itself cause the resulting executable to
     24;  be covered by the GNU General Public License. This exception does
     25;  not however invalidate any other reasons why the executable file
     26;   might be covered by the GNU General Public License.
     27;--------------------------------------------------------------------------
     28
     29        .area   _CODE
     30
     31        .globl ___strreverse
     32        .globl ___strreverse_reg
     33;
     34;char * __reverse(char *beg, char *end);
     35;
     36___strreverse::
     37        pop     bc
     38        pop     de
     39        pop     hl
     40        push    hl
     41        push    de
     42        push    bc
     43
     44;in: HL - pointer to end of string (null symbol), DE - pointer to start of string
     45;
     46___strreverse_reg::
     47        push    de
     48        jr      110$
     49100$:
     50        add     hl, de
     51        ld      a, (de)
     52        ld      c, (hl)
     53        ld      (hl), a
     54        ld      a, c
     55        ld      (de), a
     56        inc     de
     57110$:
     58        dec     hl
     59        or      a, a
     60        sbc     hl, de
     61        jr      NC, 100$
     62        pop     hl
     63        ret