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208 lines
7.4 KiB
ArmAsm
208 lines
7.4 KiB
ArmAsm
/*
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* COPYRIGHT: See COPYING in the top level directory
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* PROJECT: ReactOS kernel
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* PURPOSE: Run-Time Library
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* FILE: lib/sdk/crt/math/i386/aulldvrm_asm.s
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* PROGRAMER: Alex Ionescu (alex@relsoft.net)
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*
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* Copyright (C) 2002 Michael Ringgaard.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the project nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES// LOSS OF USE, DATA, OR PROFITS// OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <asm.inc>
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PUBLIC __aulldvrm
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/* FUNCTIONS ***************************************************************/
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.code
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__aulldvrm:
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// ulldvrm - unsigned long divide and remainder
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//
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// Purpose:
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// Does a unsigned long divide and remainder of the arguments. Arguments
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// are not changed.
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//
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// Entry:
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// Arguments are passed on the stack:
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// 1st pushed: divisor (QWORD)
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// 2nd pushed: dividend (QWORD)
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//
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// Exit:
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// EDX:EAX contains the quotient (dividend/divisor)
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// EBX:ECX contains the remainder (divided % divisor)
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// NOTE: this routine removes the parameters from the stack.
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//
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// Uses:
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// ECX
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//
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push esi
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// Set up the local stack and save the index registers. When this is done
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// the stack frame will look as follows (assuming that the expression a/b will
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// generate a call to aulldvrm(a, b)):
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//
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// -----------------
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// | |
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// |---------------|
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// | |
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// |--divisor (b)--|
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// | |
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// |---------------|
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// | |
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// |--dividend (a)-|
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// | |
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// |---------------|
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// | return addr** |
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// |---------------|
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// ESP---->| ESI |
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// -----------------
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//
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#undef DVNDLO
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#undef DVNDHI
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#undef DVSRLO
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#undef DVSRHI
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#define DVNDLO [esp + 8] // stack address of dividend (a)
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#define DVNDHI [esp + 12] // stack address of dividend (a)
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#define DVSRLO [esp + 16] // stack address of divisor (b)
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#define DVSRHI [esp + 20] // stack address of divisor (b)
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//
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// Now do the divide. First look to see if the divisor is less than 4194304K.
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// If so, then we can use a simple algorithm with word divides, otherwise
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// things get a little more complex.
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//
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mov eax,DVSRHI // check to see if divisor < 4194304K
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or eax,eax
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jnz short .L1 // nope, gotta do this the hard way
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mov ecx,DVSRLO // load divisor
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mov eax,DVNDHI // load high word of dividend
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xor edx,edx
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div ecx // get high order bits of quotient
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mov ebx,eax // save high bits of quotient
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mov eax,DVNDLO // edx:eax <- remainder:lo word of dividend
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div ecx // get low order bits of quotient
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mov esi,eax // ebx:esi <- quotient
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//
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// Now we need to do a multiply so that we can compute the remainder.
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//
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mov eax,ebx // set up high word of quotient
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mul dword ptr DVSRLO // HIWORD(QUOT) * DVSR
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mov ecx,eax // save the result in ecx
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mov eax,esi // set up low word of quotient
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mul dword ptr DVSRLO // LOWORD(QUOT) * DVSR
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add edx,ecx // EDX:EAX = QUOT * DVSR
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jmp short .L2 // complete remainder calculation
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//
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// Here we do it the hard way. Remember, eax contains DVSRHI
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//
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.L1:
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mov ecx,eax // ecx:ebx <- divisor
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mov ebx,DVSRLO
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mov edx,DVNDHI // edx:eax <- dividend
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mov eax,DVNDLO
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.L3:
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shr ecx,1 // shift divisor right one bit// hi bit <- 0
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rcr ebx,1
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shr edx,1 // shift dividend right one bit// hi bit <- 0
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rcr eax,1
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or ecx,ecx
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jnz short .L3 // loop until divisor < 4194304K
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div ebx // now divide, ignore remainder
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mov esi,eax // save quotient
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//
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// We may be off by one, so to check, we will multiply the quotient
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// by the divisor and check the result against the orignal dividend
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// Note that we must also check for overflow, which can occur if the
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// dividend is close to 2**64 and the quotient is off by 1.
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//
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mul dword ptr DVSRHI // QUOT * DVSRHI
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mov ecx,eax
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mov eax,DVSRLO
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mul esi // QUOT * DVSRLO
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add edx,ecx // EDX:EAX = QUOT * DVSR
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jc short .L4 // carry means Quotient is off by 1
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//
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// do long compare here between original dividend and the result of the
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// multiply in edx:eax. If original is larger or equal, we are ok, otherwise
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// subtract one (1) from the quotient.
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//
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cmp edx,DVNDHI // compare hi words of result and original
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ja short .L4 // if result > original, do subtract
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jb short .L5 // if result < original, we are ok
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cmp eax,DVNDLO // hi words are equal, compare lo words
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jbe short .L5 // if less or equal we are ok, else subtract
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.L4:
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dec esi // subtract 1 from quotient
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sub eax,DVSRLO // subtract divisor from result
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sbb edx,DVSRHI
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.L5:
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xor ebx,ebx // ebx:esi <- quotient
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.L2:
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//
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// Calculate remainder by subtracting the result from the original dividend.
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// Since the result is already in a register, we will do the subtract in the
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// opposite direction and negate the result.
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//
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sub eax,DVNDLO // subtract dividend from result
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sbb edx,DVNDHI
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neg edx // otherwise, negate the result
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neg eax
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sbb edx,0
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//
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// Now we need to get the quotient into edx:eax and the remainder into ebx:ecx.
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//
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mov ecx,edx
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mov edx,ebx
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mov ebx,ecx
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mov ecx,eax
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mov eax,esi
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//
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// Just the cleanup left to do. edx:eax contains the quotient.
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// Restore the saved registers and return.
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//
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pop esi
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ret 16
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END
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