/*-------------------------------------------------------------------------
   _mulint.c - routine for (unsigned) int (16 bit) multiplication

   Copyright (C) 1999, Sandeep Dutta . sandeep.dutta@usa.net

   Modifications for PIC14 by
   Copyright (C) 2019 Gonzalo Pérez de Olaguer Córdoba <salo@gpoc.es>

   This library is free software; you can redistribute it and/or modify it
   under the terms of the GNU 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this library; see the file COPYING. If not, write to the
   Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston,
   MA 02110-1301, USA.

   As a special exception, if you link this library with other files,
   some of which are compiled with SDCC, to produce an executable,
   this library does not by itself cause the resulting executable to
   be covered by the GNU General Public License. This exception does
   not however invalidate any other reasons why the executable file
   might be covered by the GNU General Public License.
-------------------------------------------------------------------------*/

/* Signed and unsigned multiplication are the same - as long as the output
   has the same precision as the input.

   Assembler-functions are provided for:
     ds390
     mcs51 small
     mcs51 small stack-auto
     mcs51 large
*/

#if !defined(__SDCC_USE_XSTACK) && !defined(_SDCC_NO_ASM_LIB_FUNCS)
#  if defined(__SDCC_ds390)
#    if !defined(__SDCC_STACK_AUTO)
#      define _MULINT_ASM_LARGE
#    endif
#  elif defined(__SDCC_mcs51)
#    if defined(__SDCC_MODEL_SMALL)
#      if defined(__SDCC_STACK_AUTO) && !defined(__SDCC_PARMS_IN_BANK1)
#        define _MULINT_ASM_SMALL_AUTO
#      else
#        define _MULINT_ASM_SMALL
#      endif
#    else // must be __SDCC_MODEL_LARGE
#      if !defined(__SDCC_STACK_AUTO)
#        define _MULINT_ASM_LARGE
#     endif
#   endif
#  endif
#endif

#if defined(_MULINT_ASM_LARGE)

#pragma save
#pragma less_pedantic
int
_mulint (int a, int b)
{
  a*b; // hush the compiler

  /* mulint=
      (int)(lsb_a*lsb_b) +
      (char)(msb_a*lsb_b)<<8 +
      (char)(lsb_a*msb_b)<<8
  */

  __asm
    mov r2,dph ; msb_a
    mov r3,dpl ; lsb_a

    mov b,r3 ; lsb_a
#if defined(__SDCC_PARMS_IN_BANK1)
    mov a,b1_0
#else
    mov dptr,#__mulint_PARM_2
    movx a,@dptr ; lsb_b
#endif
    mul ab ; lsb_a*lsb_b
    mov r0,a
    mov r1,b

    mov b,r2 ; msb_a
#if defined(__SDCC_PARMS_IN_BANK1)
    mov a,b1_0
#else
    movx a,@dptr ; lsb_b
#endif
    mul ab ; msb_a*lsb_b
    add a,r1
    mov r1,a

    mov b,r3 ; lsb_a
#if defined(__SDCC_PARMS_IN_BANK1)
    mov a,b1_1
#else
    inc dptr
    movx a,@dptr ; msb_b
#endif
    mul ab ; lsb_a*msb_b
    add a,r1

    mov dph,a
    mov dpl,r0
    ret
  __endasm;
}
#pragma restore

#elif defined(_MULINT_ASM_SMALL) || defined(_MULINT_ASM_SMALL_AUTO)

#pragma save
#pragma less_pedantic
int
_mulint_dummy (void) __naked
{
	__asm

__mulint:

	.globl __mulint

#if !defined(__SDCC_STACK_AUTO) || defined(__SDCC_PARMS_IN_BANK1)

#if defined(__SDCC_NOOVERLAY)
	.area DSEG    (DATA)
#else
	.area OSEG    (OVR,DATA)
#endif
#if defined(__SDCC_PARMS_IN_BANK1)
	#define bl 	(b1_0)
	#define bh 	(b1_1)
#else
	#define bl 	(__mulint_PARM_2)
	#define bh 	(__mulint_PARM_2 + 1)
__mulint_PARM_2:

	.globl __mulint_PARM_2

	.ds	2
#endif

	.area CSEG    (CODE)

	; globbered registers none

	mov	a,dpl			;  1  al
	mov	b,bl			;  2  bl
	mul	ab			;  4  al * bl
	xch	a,dpl			;  1  store low-byte of return value, fetch al
	push	b			;  2

	mov	b,bh			;  2  bh
	mul	ab			;  4  al * bh
	pop	b			;  2
	add	a,b			;  1
	xch	a,dph			;  1  ah -> acc

	mov	b,bl			;  2  bl
	mul	ab			;  4  ah * bl
	add	a,dph			;  1
	mov	dph,a			;  1
	ret				;  2
					; 30

#else // __SDCC_STACK_AUTO

	; globbered registers r0

	mov	a,#-2			;  1  return address 2 bytes
	add	a,sp			;  1
	mov	r0,a			;  1  r0 points to bh

	mov	a,@r0			;  1  bh
	mov	b,dpl			;  2  al
	mul	ab			;  4  al * bh
	push	acc			;  2

	mov	b,dpl			;  2  al
	dec	r0			;  1
	mov	a,@r0			;  1  bl
	mul	ab			;  4  al * bl

	mov	dpl,a			;  1  low-byte of return-value

	pop	acc			;  2
	add	a,b			;  1
	xch	a,dph			;  1  ah -> acc

	mov	b,@r0			;  2  bl
	mul	ab			;  4  ah * bl
	add	a,dph			;  1
	mov	dph,a			;  1

	ret

#endif // __SDCC_STACK_AUTO

	__endasm;
}
#pragma restore

#else

#if defined(__SDCC_hc08) || defined(__SDCC_s08) || defined(__SDCC_stm8)
// Big-endian
union uu {
	struct { unsigned char hi, lo ;} s;
        unsigned int t;
};
#else
// Little-endian
union uu {
	struct { unsigned char lo,hi ;} s;
        unsigned int t;
};
#endif

int
_mulint (int a, int b)
{
#if !defined(__SDCC_STACK_AUTO) && (defined(__SDCC_MODEL_LARGE) || defined(__SDCC_ds390))	// still needed for large
	union uu __xdata *x;
	union uu __xdata *y;
	union uu t;
        x = (union uu __xdata *)&a;
        y = (union uu __xdata *)&b;
#elif defined(__SDCC_pic14)
	union uu x;
	union uu y;
	union uu t;
        x.t = a;
        y.t = b;
#else
	register union uu *x;
	register union uu *y;
	union uu t;
        x = (union uu *)&a;
        y = (union uu *)&b;
#endif

  // sdcc is bad at handling union accesses. So we use (unsigned char)a instead of x->s.lo here.
#if defined(__SDCC_pic14)
  t.t = x.s.lo * y.s.lo;
  t.s.hi += (x.s.lo * y.s.hi) + (x.s.hi * y.s.lo);
#else
  t.t = (unsigned char)a * (unsigned char)b;
  t.s.hi += ((unsigned char)a * y->s.hi) + (x->s.hi * (unsigned char)b);
#endif

  return t.t;
}

#endif

#undef _MULINT_ASM