225 lines
10 KiB
NASM
225 lines
10 KiB
NASM
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;*****************************************************************************
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;*
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;* Open Watcom Project
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;*
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;* Portions Copyright (c) 1983-2002 Sybase, Inc. All Rights Reserved.
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;*
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;* ========================================================================
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;*
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;* This file contains Original Code and/or Modifications of Original
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;* Code as defined in and that are subject to the Sybase Open Watcom
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;* Public License version 1.0 (the 'License'). You may not use this file
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;* except in compliance with the License. BY USING THIS FILE YOU AGREE TO
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;* ALL TERMS AND CONDITIONS OF THE LICENSE. A copy of the License is
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;* provided with the Original Code and Modifications, and is also
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;* available at www.sybase.com/developer/opensource.
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;*
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;* The Original Code and all software distributed under the License are
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;* distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
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;* EXPRESS OR IMPLIED, AND SYBASE AND ALL CONTRIBUTORS HEREBY DISCLAIM
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;* ALL SUCH WARRANTIES, INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF
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;* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR
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;* NON-INFRINGEMENT. Please see the License for the specific language
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;* governing rights and limitations under the License.
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;*
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;* ========================================================================
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;*
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;* Description: WHEN YOU FIGURE OUT WHAT THIS FILE DOES, PLEASE
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;* DESCRIBE IT HERE!
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;*
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;*****************************************************************************
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;========================================================================
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;== Name: I8D ==
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;== Operation: Signed 8 byte divide ==
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;== Inputs: EDX;EAX Dividend ==
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;== ECX;EBX Divisor ==
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;== Outputs: EDX;EAX Quotient ==
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;== ECX;EBX Remainder (same sign as dividend) ==
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;== Volatile: none ==
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;== same sign as dividend for ==
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;== consistency with 8086 idiv ==
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;== and so (a/b)*b + a%b == a ==
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;== to get a 64-bit version for 386==
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;========================================================================
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include mdef.inc
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include struct.inc
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modstart i8d
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xdefp __I8D
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defpe __I8D
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or edx,edx ; check sign of dividend
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js divneg ; handle case where dividend < 0
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or ecx,ecx ; check sign of divisor
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js notU8D ; easy case if it is also positive
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; dividend >= 0, divisor >= 0
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docall __U8D ; - ...
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ret ; - ...
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; dividend >= 0, divisor < 0
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notU8D: neg ecx ; take positive value of divisor
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neg ebx ; ...
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sbb ecx,0 ; ...
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docall __U8D ; do unsigned division
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neg edx ; negate quotient
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neg eax ; ...
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sbb edx,0 ; ...
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ret ; and return
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divneg: ; dividend is negative
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neg edx ; take absolute value of dividend
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neg eax ; ...
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sbb edx,0 ; ...
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or ecx,ecx ; check sign of divisor
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jns negres ; negative result if divisor > 0
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; dividend < 0, divisor < 0
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neg ecx ; negate divisor too
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neg ebx ; ...
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sbb ecx,0 ; ...
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docall __U8D ; and do unsigned division
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neg ecx ; negate remainder
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neg ebx ; ...
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sbb ecx,0 ; ...
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ret ; and return
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; dividend < 0, divisor >= 0
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negres: docall __U8D ; do unsigned division
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neg ecx ; negate remainder
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neg ebx ; ...
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sbb ecx,0 ; ...
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neg edx ; negate quotient
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neg eax ; ...
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sbb edx,0 ; ...
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ret ; and return
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endproc __I8D
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;========================================================================
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;== Name: U8D ==
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;== Operation: Unsigned 8 byte divide ==
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;== Inputs: EDX;EAX Dividend ==
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;== ECX;EBX Divisor ==
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;== Outputs: EDX;EAX Quotient ==
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;== ECX;EBX Remainder ==
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;== Volatile: none ==
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;========================================================================
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xdefp __U8D
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defpe __U8D
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or ecx,ecx ; check for easy case
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jne noteasy ; easy if divisor is 16 bit
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dec ebx ; decrement divisor
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_if ne ; if not dividing by 1
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inc ebx ; - put divisor back
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cmp ebx,edx ; - if quotient will be >= 64K
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_if be ; - then
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;
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; 12-aug-88, added thanks to Eric Christensen from Fox Software
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; divisor < 64K, dividend >= 64K, quotient will be >= 64K
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;
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; *note* this sequence is used in ltoa's #pragmas; any bug fixes
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; should be reflected in ltoa's code bursts
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;
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mov ecx,eax ; - - save low word of dividend
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mov eax,edx ; - - get high word of dividend
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sub edx,edx ; - - zero high part
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div ebx ; - - divide bx into high part of dividend
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xchg eax,ecx ; - - swap high part of quot,low word of dvdnd
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_endif ; - endif
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div ebx ; - calculate low part
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mov ebx,edx ; - get remainder
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mov edx,ecx ; - get high part of quotient
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sub ecx,ecx ; - zero high part of remainder
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_endif ; endif
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ret ; return
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noteasy: ; have to work to do division
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;
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; check for divisor > dividend
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;
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_guess ; guess: divisor > dividend
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cmp ecx,edx ; - quit if divisor <= dividend
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_quif b ; - . . .
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_if e ; - if high parts are the same
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cmp ebx,eax ; - - compare the lower order words
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_if be ; - - if divisor <= dividend
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sub eax,ebx ; - - - calulate remainder
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mov ebx,eax ; - - - ...
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sub ecx,ecx ; - - - ...
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sub edx,edx ; - - - quotient = 1
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mov eax,1 ; - - - ...
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ret ; - - - return
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_endif ; - - endif
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_endif ; - endif
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sub ecx,ecx ; - set divisor = 0 (this will be quotient)
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sub ebx,ebx ; - ...
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xchg eax,ebx ; - return remainder = dividend
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xchg edx,ecx ; - and quotient = 0
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ret ; - return
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_endguess ; endguess
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push ebp ; save work registers
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push esi ; ...
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push edi ; ...
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sub esi,esi ; zero quotient
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mov edi,esi ; ...
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mov ebp,esi ; and shift count
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moveup: ; loop until divisor > dividend
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_shl ebx,1 ; - divisor *= 2
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_rcl ecx,1 ; - ...
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jc backup ; - know its bigger if carry out
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inc ebp ; - increment shift count
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cmp ecx,edx ; - check if its bigger yet
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jb moveup ; - no, keep going
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ja divlup ; - if below, know we're done
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cmp ebx,eax ; - check low parts (high parts equal)
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jbe moveup ; until divisor > dividend
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divlup: ; division loop
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clc ; clear carry for rotate below
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_loop ; loop
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_loop ; - loop
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_rcl esi,1 ; - - shift bit into quotient
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_rcl edi,1 ; - - . . .
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dec ebp ; - - quif( -- shift < 0 ) NB carry not changed
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js donediv ; - - ...
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backup: ; - - entry to remove last shift
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rcr ecx,1 ; - - divisor /= 2 (NB also used by 'backup')
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rcr ebx,1 ; - - ...
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sub eax,ebx ; - - dividend -= divisor
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sbb edx,ecx ; - - c=1 iff it won't go
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cmc ; - - c=1 iff it will go
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_until nc ; - until it won't go
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_loop ; - loop
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_shl esi,1 ; - - shift 0 into quotient
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_rcl edi,1 ; - - . . .
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dec ebp ; - - going to add, check if done
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js toomuch ; - - if done, we subtracted to much
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shr ecx,1 ; - - divisor /= 2
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rcr ebx,1 ; - - ...
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add eax,ebx ; - - dividend += divisor
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adc edx,ecx ; - - c = 1 iff bit of quotient should be 1
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_until c ; - until divisor will go into dividend
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_endloop ; endloop
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toomuch: ; we subtracted too much
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add eax,ebx ; dividend += divisor
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adc edx,ecx ; ...
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donediv: ; now quotient in di;si, remainder in dx;ax
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mov ebx,eax ; move remainder to cx;bx
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mov ecx,edx ; ...
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mov eax,esi ; move quotient to dx;ax
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mov edx,edi ; ...
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pop edi ; restore registers
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pop esi ; ...
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pop ebp ; ...
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ret ; and return
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endproc __U8D
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endmod
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end
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