188 lines
4.2 KiB
NASM
188 lines
4.2 KiB
NASM
page ,132
|
|
title uldiv - unsigned long divide routine
|
|
;***
|
|
;uldiv.asm - unsigned long divide routine
|
|
;
|
|
; Copyright (c) 1985-1998 Microsoft Corporation
|
|
;
|
|
;Purpose:
|
|
; defines the unsigned long divide routine
|
|
; the following routines are created:
|
|
; __aFuldiv (large, medium models)
|
|
; __aNuldiv (small, compact models)
|
|
;
|
|
;*******************************************************************************
|
|
|
|
.xlist
|
|
|
|
?PLM = 0
|
|
?WIN = 1
|
|
PMODE= 1
|
|
memM = 1
|
|
|
|
|
|
include cmacros.inc
|
|
include cmphlp.inc
|
|
include mm.inc
|
|
.list
|
|
|
|
CreateSeg FIXMIDI, MidiFix, word, public, CODE
|
|
|
|
sBegin MidiFix
|
|
assumes cs,MidiFix
|
|
assumes ds,data
|
|
|
|
page
|
|
;***
|
|
;uldiv - unsigned long divide
|
|
;
|
|
;Purpose:
|
|
; Does a unsigned long divide of the arguments. Arguments are
|
|
; not changed.
|
|
;
|
|
;Entry:
|
|
; Arguments are passed on the stack:
|
|
; 1st pushed: divisor (DWORD)
|
|
; 2nd pushed: dividend (DWORD)
|
|
;
|
|
;Exit:
|
|
; DX:AX contains the quotient (dividend/divisor)
|
|
; NOTE: this routine removes the parameters from the stack.
|
|
;
|
|
;Uses:
|
|
; CX
|
|
;
|
|
;Exceptions:
|
|
;
|
|
;*******************************************************************************
|
|
|
|
; ASGN uldiv
|
|
if sizeC
|
|
cProc _aFuldiv,<PUBLIC>,<>
|
|
|
|
else
|
|
cProc _aNuldiv,<PUBLIC>,<>
|
|
endif
|
|
|
|
ParmD DVND1
|
|
ParmD DVSR1
|
|
cBegin
|
|
|
|
push bx
|
|
push si
|
|
|
|
; Set up the local stack and save the index registers. When this is done
|
|
; the stack frame will look as follows (assuming that the expression a/b will
|
|
; generate a call to uldiv(a, b)):
|
|
;
|
|
; -----------------
|
|
; | |
|
|
; |---------------|
|
|
; | |
|
|
; |--divisor (b)--|
|
|
; | |
|
|
; |---------------|
|
|
; | |
|
|
; |--dividend (a)-|
|
|
; | |
|
|
; |---------------|
|
|
; | return addr** |
|
|
; |---------------|
|
|
; BP----->| old BP |
|
|
; |---------------|
|
|
; | BX |
|
|
; |---------------|
|
|
; SP----->| SI |
|
|
; -----------------
|
|
;
|
|
; ** - 2 bytes if small/compact model; 4 bytes if medium/large model
|
|
|
|
DVND equ BPARGBAS[bp] ; stack address of dividend (a)
|
|
DVSR equ BPARGBAS+4[bp] ; stack address of divisor (b)
|
|
|
|
;
|
|
; Now do the divide. First look to see if the divisor is less than 64K.
|
|
; If so, then we can use a simple algorithm with word divides, otherwise
|
|
; things get a little more complex.
|
|
;
|
|
|
|
mov ax,HIWORD(DVSR) ; check to see if divisor < 64K
|
|
or ax,ax
|
|
jnz L1 ; nope, gotta do this the hard way
|
|
mov cx,LOWORD(DVSR) ; load divisor
|
|
mov ax,HIWORD(DVND) ; load high word of dividend
|
|
xor dx,dx
|
|
div cx ; get high order bits of quotient
|
|
mov bx,ax ; save high bits of quotient
|
|
mov ax,LOWORD(DVND) ; dx:ax <- remainder:lo word of dividend
|
|
div cx ; get low order bits of quotient
|
|
mov dx,bx ; dx:ax <- quotient hi:quotient lo
|
|
jmp short L2 ; restore stack and return
|
|
|
|
;
|
|
; Here we do it the hard way. Remember, ax contains DVSRHI
|
|
;
|
|
|
|
L1:
|
|
mov cx,ax ; cx:bx <- divisor
|
|
mov bx,LOWORD(DVSR)
|
|
mov dx,HIWORD(DVND) ; dx:ax <- dividend
|
|
mov ax,LOWORD(DVND)
|
|
L3:
|
|
shr cx,1 ; shift divisor right one bit; hi bit <- 0
|
|
rcr bx,1
|
|
shr dx,1 ; shift dividend right one bit; hi bit <- 0
|
|
rcr ax,1
|
|
or cx,cx
|
|
jnz L3 ; loop until divisor < 64K
|
|
div bx ; now divide, ignore remainder
|
|
mov si,ax ; save quotient
|
|
|
|
;
|
|
; We may be off by one, so to check, we will multiply the quotient
|
|
; by the divisor and check the result against the orignal dividend
|
|
; Note that we must also check for overflow, which can occur if the
|
|
; dividend is close to 2**32 and the quotient is off by 1.
|
|
;
|
|
|
|
mul word ptr HIWORD(DVSR) ; QUOT * HIWORD(DVSR)
|
|
xchg cx,ax ; "mov cx,ax" but only 1 byte
|
|
mov ax,LOWORD(DVSR)
|
|
mul si ; QUOT * LOWORD(DVSR)
|
|
add dx,cx ; DX:AX = QUOT * DVSR
|
|
jc L4 ; carry means Quotient is off by 1
|
|
|
|
;
|
|
; do long compare here between original dividend and the result of the
|
|
; multiply in dx:ax. If original is larger or equal, we are ok, otherwise
|
|
; subtract one (1) from the quotient.
|
|
;
|
|
|
|
cmp dx,HIWORD(DVND) ; compare hi words of result and original
|
|
ja L4 ; if result > original, do subtract
|
|
jb L5 ; if result < original, we are ok
|
|
cmp ax,LOWORD(DVND) ; hi words are equal, compare lo words
|
|
jbe L5 ; if less or equal we are ok, else subtract
|
|
L4:
|
|
dec si ; subtract 1 from quotient
|
|
L5:
|
|
xor dx,dx ; dx:ax <- quotient
|
|
xchg ax,si ; "mov ax,si" but only 1 byte
|
|
|
|
;
|
|
; Just the cleanup left to do. dx:ax contains the quotient.
|
|
; Restore the saved registers and return.
|
|
;
|
|
|
|
L2:
|
|
|
|
pop si
|
|
pop bx
|
|
|
|
cEnd <nolocals>
|
|
return 8
|
|
|
|
sEnd
|
|
|
|
end
|