sdcc/device/lib/_moduint.c

   1 /*-------------------------------------------------------------------------
   2    _moduint.c - routine for unsigned int (16 bit) modulus
   3
   4    Copyright (C) 1999, Sandeep Dutta . sandeep.dutta@usa.net
   5    Bug fixes by Martijn van Balen, aed@iae.nl
   6
   7    This library is free software; you can redistribute it and/or modify it
   8    under the terms of the GNU General Public License as published by the
   9    Free Software Foundation; either version 2, or (at your option) any
  10    later version.
  11
  12    This library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this library; see the file COPYING. If not, write to the
  19    Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
  20    MA 02110-1301, USA.
  21
  22    As a special exception, if you link this library with other files,
  23    some of which are compiled with SDCC, to produce an executable,
  24    this library does not by itself cause the resulting executable to
  25    be covered by the GNU General Public License. This exception does
  26    not however invalidate any other reasons why the executable file
  27    might be covered by the GNU General Public License.
  28 -------------------------------------------------------------------------*/
  29
  30 /*   Assembler-functions are provided for:
  31      mcs51 small
  32      mcs51 small stack-auto
  33 */
  34
  35 #include <sdcc-lib.h>
  36
  37 #if !defined(__SDCC_USE_XSTACK) && !defined(_SDCC_NO_ASM_LIB_FUNCS)
  38 #  if defined(__SDCC_mcs51)
  39 #    if defined(__SDCC_MODEL_SMALL)
  40 #      if defined(__SDCC_STACK_AUTO)
  41 #        define _MODUINT_ASM_SMALL_AUTO
  42 #      else
  43 #        define _MODUINT_ASM_SMALL
  44 #      endif
  45 #    endif
  46 #  endif
  47 #endif
  48
  49 #if defined _MODUINT_ASM_SMALL || defined _MODUINT_ASM_SMALL_AUTO
  50
  51 static void
  52 _moduint_dummy (void) __naked
  53 {
  54         __asm
  55
  56         .globl __moduint
  57
  58 __moduint:
  59
  60         #define count   r2
  61         #define al      dpl
  62         #define ah      dph
  63
  64 #if defined(__SDCC_STACK_AUTO) && !defined(__SDCC_PARMS_IN_BANK1)
  65
  66         ar0 = 0                 ; BUG register set is not considered
  67         ar1 = 1
  68
  69         .globl __modint
  70
  71         mov     a,sp
  72         add     a,#-2           ; 2 bytes return address
  73         mov     r0,a            ; r0 points to bh
  74         mov     ar1,@r0         ; load bh
  75         dec     r0
  76         mov     ar0,@r0         ; load bl
  77
  78         #define bl      r0
  79         #define bh      r1
  80
  81 __modint:                       ; entry point for __modsint
  82
  83
  84 #else // __SDCC_STACK_AUTO
  85
  86 #if !defined(__SDCC_PARMS_IN_BANK1)
  87 #if defined(__SDCC_NOOVERLAY)
  88         .area DSEG    (DATA)
  89 #else
  90         .area OSEG    (OVR,DATA)
  91 #endif
  92
  93         .globl __moduint_PARM_2
  94         .globl __modsint_PARM_2
  95
  96 __moduint_PARM_2:
  97 __modsint_PARM_2:
  98         .ds     2
  99
 100         .area CSEG    (CODE)
 101
 102         #define bl      (__moduint_PARM_2)
 103         #define bh      (__moduint_PARM_2 + 1)
 104 #else
 105         #define bl      (b1_0)
 106         #define bh      (b1_1)
 107 #endif
 108 #endif // __SDCC_STACK_AUTO
 109
 110         mov     a,bl            ; avoid endless loop
 111         orl     a,bh
 112         jz      div_by_0
 113
 114         mov     count,#1
 115
 116 loop1:  mov     a,bl            ; b <<= 1
 117         add     a,acc
 118         mov     bl,a
 119         mov     a,bh
 120         rlc     a
 121         jc      msbset
 122         mov     bh,a
 123
 124         mov     a,al            ; a - b
 125         subb    a,bl            ; here carry is always clear
 126         mov     a,ah
 127         subb    a,bh
 128
 129         jc      start
 130
 131         inc     count
 132         sjmp    loop1
 133
 134 start:  clr     c
 135         mov     a,bh            ; b >>= 1;
 136 msbset: rrc     a
 137         mov     bh,a
 138         mov     a,bl
 139         rrc     a
 140         mov     bl,a
 141
 142 loop2:  clr     c
 143         mov     a,al            ; a - b
 144         subb    a,bl
 145
 146         mov     b,a
 147         mov     a,ah
 148         subb    a,bh
 149
 150         jc      smaller         ; a >= b?
 151
 152         mov     ah,a            ; -> yes;  a = a - b;
 153         mov     al,b
 154 smaller:                        ; -> no
 155         clr     c
 156         mov     a,bh            ; b >>= 1;
 157         rrc     a
 158         mov     bh,a
 159         mov     a,bl
 160         rrc     a
 161         mov     bl,a
 162
 163         djnz    count,loop2
 164 div_by_0:
 165         ret
 166
 167         __endasm;
 168 }
 169
 170 #else  // defined _MODUINT_ASM_SMALL || defined _MODUINT_ASM_SMALL_AUTO
 171
 172 #define MSB_SET(x) ((x >> (8*sizeof(x)-1)) & 1)
 173
 174 unsigned int
 175 _moduint (unsigned int a, unsigned int b) __SDCC_NONBANKED
 176 {
 177   unsigned char count = 0;
 178
 179   while (!MSB_SET(b))
 180   {
 181     b <<= 1;
 182     if (b > a)
 183     {
 184       b >>=1;
 185       break;
 186     }
 187     count++;
 188   }
 189   do
 190   {
 191     if (a >= b)
 192       a -= b;
 193     b >>= 1;
 194   }
 195   while (count--);
 196   return a;
 197 }
 198
 199 #endif  // defined _MODUINT_ASM_SMALL || defined _MODUINT_ASM_SMALL_AUTO