gbdk-releases/sdcc/device/lib/_modulong.c

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/*-------------------------------------------------------------------------
_modulong.c - routine for modulus of 32 bit unsigned long
Written By - Sandeep Dutta . sandeep.dutta@usa.net (1999)
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
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
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
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Library General Public License for more details.
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
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.
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:
mcs51 small
mcs51 small stack-auto
*/
#if !defined(SDCC_USE_XSTACK) && !defined(_SDCC_NO_ASM_LIB_FUNCS)
# if defined(SDCC_mcs51)
# if defined(SDCC_MODEL_SMALL)
# if defined(SDCC_STACK_AUTO)
# define _MODULONG_ASM_SMALL_AUTO
# else
# define _MODULONG_ASM_SMALL
# endif
# endif
# endif
#endif
#if defined _MODULONG_ASM_SMALL
static void
_modlong_dummy (void) _naked
{
_asm
.globl __modulong
__modulong:
#if defined(SDCC_NOOVERLAY)
.area DSEG (DATA)
#else
.area OSEG (OVR,DATA)
#endif
.globl __modulong_PARM_2
.globl __modslong_PARM_2
__modulong_PARM_2:
__modslong_PARM_2:
.ds 4
.area CSEG (CODE)
#define count r0
#define a0 dpl
#define a1 dph
#define a2 b
#define a3 r1
#define b0 (__modulong_PARM_2)
#define b1 (__modulong_PARM_2 + 1)
#define b2 (__modulong_PARM_2 + 2)
#define b3 (__modulong_PARM_2 + 3)
; parameter a comes in a, b, dph, dpl
mov a3,a ; save parameter a3
mov a,b0 ; b == 0? avoid endless loop
orl a,b1
orl a,b2
orl a,b3
jz div_by_0
mov count,#0
clr c ; when loop1 jumps immediately to loop2
loop1: inc count
mov a,b3 ; if (!MSB_SET(b))
jb acc.7,loop2
mov a,b0 ; b <<= 1
add a,acc
mov b0,a
mov a,b1
rlc a
mov b1,a
mov a,b2
rlc a
mov b2,a
mov a,b3
rlc a
mov b3,a
mov a,a0 ; a - b
subb a,b0 ; here carry is always clear
mov a,a1
subb a,b1
mov a,a2
subb a,b2
mov a,a3
subb a,b3
jnc loop1
clr c
mov a,b3 ; b >>= 1;
rrc a
mov b3,a
mov a,b2
rrc a
mov b2,a
mov a,b1
rrc a
mov b1,a
mov a,b0
rrc a
mov b0,a
loop2: ; clr c never set
mov a,a0 ; a - b
subb a,b0
mov r4,a
mov a,a1
subb a,b1
mov r5,a
mov a,a2
subb a,b2
mov r6,a
mov a,a3
subb a,b3
jc smaller ; a >= b?
mov a3,a ; -> yes; a = a - b;
mov a2,r6
mov a1,r5
mov a0,r4
smaller: ; -> no
clr c
mov a,b3 ; b >>= 1;
rrc a
mov b3,a
mov a,b2
rrc a
mov b2,a
mov a,b1
rrc a
mov b1,a
mov a,b0
rrc a
mov b0,a
djnz count,loop2
mov a,a3 ; prepare the return value
div_by_0:
ret
_endasm ;
}
#elif defined _MODULONG_ASM_SMALL_AUTO
static void
_modlong_dummy (void) _naked
{
_asm
.globl __modulong
__modulong:
#define count r0
#define a0 dpl
#define a1 dph
#define a2 b
#define a3 r1
#define b0 r2
#define b1 r3
#define b2 r4
#define b3 r5
ar2 = 2 ; BUG register set is not considered
ar3 = 3
ar4 = 4
ar5 = 5
.globl __modlong ; entry point for __modslong
; parameter a comes in a, b, dph, dpl
mov a3,a ; save parameter a3
mov a,sp
add a,#-2-3 ; 2 bytes return address, 3 bytes param b
mov r0,a ; r1 points to b0
mov ar2,@r0 ; load b0
inc r0 ; r0 points to b1
mov ar3,@r0 ; b1
inc r0
mov ar4,@r0 ; b2
inc r0
mov ar5,@r0 ; b3
__modlong: ; entry point for __modslong
; a in r1, b, dph, dpl
; b in r5, r4, r3, r2
mov count,#0
mov a,b0 ; b == 0? avoid endless loop
orl a,b1
orl a,b2
orl a,b3
jz div_by_0
mov count,#0
clr c ; when loop1 jumps immediately to loop2
loop1: inc count
mov a,b3 ; if (!MSB_SET(b))
jb acc.7,loop2
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mov a,b0 ; b <<= 1
add a,acc
mov b0,a
mov a,b1
rlc a
mov b1,a
mov a,b2
rlc a
mov b2,a
mov a,b3
rlc a
mov b3,a
mov a,a0 ; a - b
subb a,b0 ; here carry is always clear
mov a,a1
subb a,b1
mov a,a2
subb a,b2
mov a,a3
subb a,b3
jnc loop1
clr c
mov a,b3 ; b >>= 1;
rrc a
mov b3,a
mov a,b2
rrc a
mov b2,a
mov a,b1
rrc a
mov b1,a
mov a,b0
rrc a
mov b0,a
loop2: ; clr c never set
mov a,a0 ; a - b
subb a,b0
mov a,a1
subb a,b1
mov r6,a ; d1
mov a,a2
subb a,b2
mov r7,a ; d2
mov a,a3
subb a,b3
jc smaller ; a >= b?
mov a3,a ; -> yes; a = a - b;
mov a2,r7
mov a1,r6
mov a,a0
subb a,b0
mov a0,a
smaller: ; -> no
clr c
mov a,b3 ; b >>= 1;
rrc a
mov b3,a
mov a,b2
rrc a
mov b2,a
mov a,b1
rrc a
mov b1,a
mov a,b0
rrc a
mov b0,a
djnz count,loop2
mov a,a3 ; prepare the return value
div_by_0:
ret
_endasm ;
}
#else // _MODULONG_ASM
#define MSB_SET(x) ((x >> (8*sizeof(x)-1)) & 1)
unsigned long
_modulong (unsigned long a, unsigned long b)
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{
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unsigned char count = 0;
while (!MSB_SET(b))
{
b <<= 1;
if (b > a)
{
b >>=1;
break;
}
count++;
}
do
{
if (a >= b)
a -= b;
b >>= 1;
}
while (count--);
return a;
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}
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#endif // _MODULONG_ASM