;Subject: Quick routines for 16-bit large-integer arithmetic Basic library.
;Author : Sjoerd.J.Schaper - vspickelen@zonnet.nl
;Date   : 07-07-2004
;Code   : Assembly
.MODEL Medium, Basic
.386

MB equ 08000h           ;storage base
M1 equ 07FFFh           ;masks MB - 1
M2 equ 03FFF8000h       ;(MB - 1)* MB
LB equ 0Fh              ;bitlength

.CODE

PUBLIC EstQ             ;n(j, ..)* MB^2 + n(j-1, ..)* MB + n(j-2, ..)
EstQ PROC               ;45-bit dividend \ 30-bit divisor,
  mov bx,sp             ;15-bit quotient is returned in ax
  push ds
  push si

  xor edx,edx
  mov si,[bx+4]         ;point si to the long divisor
  mov ecx,[si]          ;load value
  lds si,[bx+6]         ;point ds:si to h.o. array element
  mov dx,[si]           ;load it
  mov eax,[si-4]        ;load both l.o. array elements
  mov bx,ax             ;save low word, msb is 0
  shr eax,1             ;shift-right dword
  and eax,M2            ;mask off bits 0..14
  or  ax,bx             ;paste back low word

  xor ebx,ebx
  shr dx,1              ;shift-right 2 bits in edx:ebx
  rcr ebx,1
  shr dx,1
  rcr ebx,1
  or  eax,ebx           ;paste in 2 high bits with l.o. elements in 0..29

  div ecx               ;edx:eax / ecx integer division
  mov edx,MB
  cmp edx,eax           ;check if base > quotient
  ja  eind
  mov ax,M1             ;if not, return base - 1

eind:
  pop si
  pop ds
retf 6
EstQ ENDP

;This routine does not check for segment crossings,
;so do not compile the LargeInt-library with the /Ah switch,
;or replace EstQ with its Basic counterpart, if needed.

PUBLIC SftL
SftL PROC
push bp
mov bp,sp
  mov bx,[bp+6]         ;move bits-to-shift into cx
  mov cx,[bx]
  mov bx,[bp+8]         ;get value-to-shift address
  shl dword ptr[bx],cl  ;shift-left
pop bp
retf 4
SftL ENDP

PUBLIC SftR
SftR PROC
push bp
mov bp,sp
  mov bx,[bp+6]
  mov cx,[bx]
  mov bx,[bp+8]
  shr dword ptr[bx],cl  ;shift-right
pop bp
retf 4
SftR ENDP

;As SftL and SftR reference 16-bit offset addresses only,
;they accept no $Dynamic array elements as argument.

END