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gbdk-lib/libc/_divulong.c

/*-------------------------------------------------------------------------
   _divulong.c - routine for division of 32 bit unsigned long

             Ecrit par -  Jean-Louis Vern . jlvern@writeme.com (1999)

   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
   Free Software Foundation; either version 2, or (at your option) any
   later version.

   This library 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 Library General Public License for more details.

   You should have received a copy of the GNU Library General Public License
   along with this program; if not, write to the Free Software
   Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

   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
   what you give them.   Help stamp out software-hoarding!
-------------------------------------------------------------------------*/

/*   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 _DIVULONG_ASM_SMALL_AUTO
#      else
#        define _DIVULONG_ASM_SMALL
#      endif
#    endif
#  endif
#endif

#if defined _DIVULONG_ASM_SMALL

static void
_divlong_dummy (void) _naked
{
	_asm

		.globl __divulong

	__divulong:

		#define count   r2

		#define a0	dpl
		#define a1	dph
		#define a2	b
		#define a3	r3

		#define reste0	r4
		#define reste1	r5
		#define reste2	r6
		#define reste3	r7

#if defined(SDCC_NOOVERLAY)
		.area DSEG    (DATA)
#else
		.area OSEG    (OVR,DATA)
#endif

		.globl __divulong_PARM_2
		.globl __divslong_PARM_2

	__divulong_PARM_2:
	__divslong_PARM_2:
		.ds	4

		.area CSEG    (CODE)

		#define b0      (__divulong_PARM_2)
		#define b1      (__divulong_PARM_2 + 1)
		#define b2      (__divulong_PARM_2 + 2)
		#define b3      (__divulong_PARM_2 + 3)

					; parameter a comes in a, b, dph, dpl
		mov	a3,a		; save parameter a3

		mov	count,#32
		clr	a
		mov	reste0,a
		mov	reste1,a
		mov	reste2,a
		mov	reste3,a

	; optimization  loop in lp0 until the first bit is shifted into rest

	lp0:	mov	a,a0		; a <<= 1
		add	a,a0
		mov	a0,a
		mov	a,a1
		rlc	a
		mov	a1,a
		mov	a,a2
		rlc	a
		mov	a2,a
		mov	a,a3
		rlc	a
		mov	a3,a

		jc	in_lp
		djnz	count,lp0

		sjmp	exit

	loop:	mov	a,a0		; a <<= 1
		add	a,a0
		mov	a0,a
		mov	a,a1
		rlc	a
		mov	a1,a
		mov	a,a2
		rlc	a
		mov	a2,a
		mov	a,a3
		rlc	a
		mov	a3,a

	in_lp:	mov	a,reste0	; reste <<= 1
		rlc	a		;   feed in carry
		mov	reste0,a
		mov	a,reste1
		rlc	a
		mov	reste1,a
		mov	a,reste2
		rlc	a
		mov	reste2,a
		mov	a,reste3
		rlc	a
		mov	reste3,a

		mov	a,reste0	; reste - b
		subb	a,b0		; carry is always clear here, because
					; reste <<= 1 never overflows
		mov	a,reste1
		subb	a,b1
		mov	a,reste2
		subb	a,b2
		mov	a,reste3
		subb	a,b3

		jc	minus		; reste >= b?

					; -> yes;  reste -= b;
		mov	a,reste0
		subb	a,b0		; carry is always clear here (jc)
		mov	reste0,a
		mov	a,reste1
		subb	a,b1
		mov	reste1,a
		mov	a,reste2
		subb	a,b2
		mov	reste2,a
		mov	a,reste3
		subb	a,b3
		mov	reste3,a

		orl	a0,#1

	minus:	djnz	count,loop	; -> no

	exit:	mov	a,a3		; prepare the return value
		ret

	_endasm ;
}

#elif defined _DIVULONG_ASM_SMALL_AUTO

static void
_divlong_dummy (void) _naked
{
	_asm

		.globl __divulong

	__divulong:

		#define count   r2

		#define a0	dpl
		#define a1	dph
		#define a2	b
		#define a3	r3

		#define reste0	r4
		#define reste1	r5
		#define reste2	r6
		#define reste3	r7

		.globl __divlong	; entry point for __divslong

		#define b0	r1

		ar0 = 0			; BUG register set is not considered
		ar1 = 1

					; 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		; r0 points to b0

	__divlong:			; entry point for __divslong

		mov	ar1,@r0		; load b0
		inc	r0		; r0 points to b1

		mov	count,#32
		clr	a
		mov	reste0,a
		mov	reste1,a
		mov	reste2,a
		mov	reste3,a

	; optimization  loop in lp0 until the first bit is shifted into rest

	lp0:	mov	a,a0		; a <<= 1
		add	a,a0
		mov	a0,a
		mov	a,a1
		rlc	a
		mov	a1,a
		mov	a,a2
		rlc	a
		mov	a2,a
		mov	a,a3
		rlc	a
		mov	a3,a

		jc	in_lp
		djnz	count,lp0

		sjmp	exit

	loop:	mov	a,a0		; a <<= 1
		add	a,a0
		mov	a0,a
		mov	a,a1
		rlc	a
		mov	a1,a
		mov	a,a2
		rlc	a
		mov	a2,a
		mov	a,a3
		rlc	a
		mov	a3,a

	in_lp:	mov	a,reste0	; reste <<= 1
		rlc	a		;   feed in carry
		mov	reste0,a
		mov	a,reste1
		rlc	a
		mov	reste1,a
		mov	a,reste2
		rlc	a
		mov	reste2,a
		mov	a,reste3
		rlc	a
		mov	reste3,a

		mov	a,reste0	; reste - b
		subb	a,b0		; carry is always clear here, because
					; reste <<= 1 never overflows
		mov	a,reste1
		subb	a,@r0		; b1
		mov	a,reste2
		inc	r0
		subb	a,@r0		; b2
		mov	a,reste3
		inc	r0
		subb	a,@r0		; b3
		dec	r0
		dec	r0

		jc	minus		; reste >= b?

					; -> yes;  reste -= b;
		mov	a,reste0
		subb	a,b0		; carry is always clear here (jc)
		mov	reste0,a
		mov	a,reste1
		subb	a,@r0		; b1
		mov	reste1,a
		mov	a,reste2
		inc	r0
		subb	a,@r0		; b2
		mov	reste2,a
		mov	a,reste3
		inc	r0
		subb	a,@r0		; b3
		mov	reste3,a
		dec	r0
		dec	r0

		orl	a0,#1

	minus:	djnz	count,loop	; -> no

	exit:	mov	a,a3		; prepare the return value
		ret

	_endasm ;
}

#else // _DIVULONG_ASM

#define MSB_SET(x) ((x >> (8*sizeof(x)-1)) & 1)

unsigned long
_divulong (unsigned long a, unsigned long b)
{
  unsigned long reste = 0L;
  unsigned char count = 32;
  #if defined(__SDCC_STACK_AUTO) || defined(__SDCC_z80) || defined(__SDCC_sm83) || defined(__SDCC_mos6502)
    char c;
  #else
    bit c;
  #endif

  do
  {
    // reste: a <- 0;
    c = MSB_SET(a);
    a <<= 1;
    reste <<= 1;
    if (c)
      reste |= 1L;

    if (reste >= b)
    {
      reste -= b;
      // a <- (result = 1)
      a |= 1L;
    }
  }
  while (--count);
  return a;
}

#endif // _DIVULONG_ASM

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