194 lines
3.6 KiB
C
194 lines
3.6 KiB
C
/*-------------------------------------------------------------------------
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_moduint.c :- routine for unsigned int (16 bit) modulus
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Written By - Sandeep Dutta . sandeep.dutta@usa.net (1999)
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Bug fixes by Martijn van Balen, aed@iae.nl
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This library is free software; you can redistribute it and/or modify it
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under the terms of the GNU Library General Public License as published by the
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Free Software Foundation; either version 2, or (at your option) any
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later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Library General Public License for more details.
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You should have received a copy of the GNU Library General Public License
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along with this program; if not, write to the Free Software
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Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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In other words, you are welcome to use, share and improve this program.
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You are forbidden to forbid anyone else to use, share and improve
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what you give them. Help stamp out software-hoarding!
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-------------------------------------------------------------------------*/
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/* Assembler-functions are provided for:
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mcs51 small
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mcs51 small stack-auto
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*/
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#if !defined(SDCC_USE_XSTACK) && !defined(_SDCC_NO_ASM_LIB_FUNCS)
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# if defined(SDCC_mcs51)
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# if defined(SDCC_MODEL_SMALL)
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# if defined(SDCC_STACK_AUTO)
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# define _MODUINT_ASM_SMALL_AUTO
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# else
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# define _MODUINT_ASM_SMALL
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# endif
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# endif
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# endif
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#endif
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#if defined _MODUINT_ASM_SMALL || defined _MODUINT_ASM_SMALL_AUTO
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static void
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_moduint_dummy (void) _naked
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{
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_asm
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.globl __moduint
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__moduint:
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#define count r2
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#define al dpl
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#define ah dph
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#ifdef SDCC_STACK_AUTO
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ar0 = 0 ; BUG register set is not considered
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ar1 = 1
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.globl __modint
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mov a,sp
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add a,#-2 ; 2 bytes return address
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mov r0,a ; r0 points to bh
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mov ar1,@r0 ; load bh
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dec r0
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mov ar0,@r0 ; load bl
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#define bl r0
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#define bh r1
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__modint: ; entry point for __modsint
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#else // SDCC_STACK_AUTO
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#if defined(SDCC_NOOVERLAY)
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.area DSEG (DATA)
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#else
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.area OSEG (OVR,DATA)
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#endif
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.globl __moduint_PARM_2
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.globl __modsint_PARM_2
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__moduint_PARM_2:
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__modsint_PARM_2:
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.ds 2
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.area CSEG (CODE)
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#define bl (__moduint_PARM_2)
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#define bh (__moduint_PARM_2 + 1)
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#endif // SDCC_STACK_AUTO
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mov a,bl ; avoid endless loop
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orl a,bh
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jz div_by_0
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mov count,#1
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loop1: mov a,bl ; b <<= 1
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add a,acc
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mov bl,a
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mov a,bh
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rlc a
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jc msbset
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mov bh,a
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mov a,al ; a - b
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subb a,bl ; here carry is always clear
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mov a,ah
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subb a,bh
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jc start
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inc count
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sjmp loop1
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start: clr c
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mov a,bh ; b >>= 1;
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msbset: rrc a
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mov bh,a
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mov a,bl
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rrc a
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mov bl,a
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loop2: clr c
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mov a,al ; a - b
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subb a,bl
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mov b,a
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mov a,ah
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subb a,bh
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jc smaller ; a >= b?
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mov ah,a ; -> yes; a = a - b;
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mov al,b
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smaller: ; -> no
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clr c
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mov a,bh ; b >>= 1;
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rrc a
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mov bh,a
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mov a,bl
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rrc a
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mov bl,a
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djnz count,loop2
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div_by_0:
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ret
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_endasm ;
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}
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#else // defined _MODUINT_ASM_SMALL || defined _MODUINT_ASM_SMALL_AUTO
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#define MSB_SET(x) ((x >> (8*sizeof(x)-1)) & 1)
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unsigned int
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_moduint (unsigned int a, unsigned int b)
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{
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unsigned char count = 0;
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while (!MSB_SET(b))
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{
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b <<= 1;
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if (b > a)
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{
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b >>=1;
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break;
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}
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count++;
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}
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do
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{
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if (a >= b)
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a -= b;
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b >>= 1;
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}
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while (count--);
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return a;
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}
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#endif // defined _MODUINT_ASM_SMALL || defined _MODUINT_ASM_SMALL_AUTO
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