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494 lines
13 KiB
ArmAsm
494 lines
13 KiB
ArmAsm
.file "reg_u_div.S"
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/*
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* reg_u_div.S
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*
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* Core division routines
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*
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*
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* Copyright (C) 1992, 1993 W. Metzenthen, 22 Parker St, Ormond,
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* Vic 3163, Australia.
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* E-mail apm233m@vaxc.cc.monash.edu.au
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* All rights reserved.
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*
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* This copyright notice covers the redistribution and use of the
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* FPU emulator developed by W. Metzenthen. It covers only its use
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* in the 386BSD operating system. Any other use is not permitted
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* under this copyright.
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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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* 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 include information specifying
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* that source code for the emulator is freely available and include
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* either:
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* a) an offer to provide the source code for a nominal distribution
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* fee, or
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* b) list at least two alternative methods whereby the source
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* can be obtained, e.g. a publically accessible bulletin board
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* and an anonymous ftp site from which the software can be
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* downloaded.
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* 3. All advertising materials specifically mentioning features or use of
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* this emulator must acknowledge that it was developed by W. Metzenthen.
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* 4. The name of W. Metzenthen may not be used to endorse or promote
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* products derived from this software without specific prior written
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* permission.
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*
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
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* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
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* AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
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* W. METZENTHEN BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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*/
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/*---------------------------------------------------------------------------+
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| Kernel for the division routines. |
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| |
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| void reg_u_div(FPU_REG *a, FPU_REG *a, |
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| FPU_REG *dest, unsigned int control_word) |
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| Does not compute the destination exponent, but does adjust it. |
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+---------------------------------------------------------------------------*/
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#include "exception.h"
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#include "fpu_asm.h"
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#include "control_w.h"
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/* #define dSIGL(x) (x) */
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/* #define dSIGH(x) 4(x) */
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.data
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/*
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Local storage:
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Result: accum_3:accum_2:accum_1:accum_0
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Overflow flag: ovfl_flag
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*/
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.align 2,0
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accum_3:
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.long 0
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accum_2:
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.long 0
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accum_1:
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.long 0
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accum_0:
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.long 0
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result_1:
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.long 0
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result_2:
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.long 0
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ovfl_flag:
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.byte 0
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.text
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.align 2,144
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.globl _reg_u_div
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.globl _divide_kernel
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_reg_u_div:
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pushl %ebp
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movl %esp,%ebp
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pushl %esi
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pushl %edi
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pushl %ebx
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movl PARAM1,%esi /* pointer to num */
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movl PARAM2,%ebx /* pointer to denom */
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movl PARAM3,%edi /* pointer to answer */
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#ifdef DENORM_OPERAND
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movl EXP(%esi),%eax
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cmpl EXP_UNDER,%eax
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jg xOp1_not_denorm
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call _denormal_operand
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orl %eax,%eax
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jnz FPU_Arith_exit
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xOp1_not_denorm:
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movl EXP(%ebx),%eax
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cmpl EXP_UNDER,%eax
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jg xOp2_not_denorm
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call _denormal_operand
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orl %eax,%eax
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jnz FPU_Arith_exit
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xOp2_not_denorm:
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#endif DENORM_OPERAND
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_divide_kernel:
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#ifdef PARANOID
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/* testl $0x80000000, SIGH(%esi) *//* Dividend */
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/* je L_bugged */
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testl $0x80000000, SIGH(%ebx) /* Divisor*/
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je L_bugged
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#endif PARANOID
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/* Check if the divisor can be treated as having just 32 bits */
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cmpl $0,SIGL(%ebx)
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jnz L_Full_Division /* Can't do a quick divide */
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/* We should be able to zip through the division here */
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movl SIGH(%ebx),%ecx /* The divisor */
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movl SIGH(%esi),%edx /* Dividend */
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movl SIGL(%esi),%eax /* Dividend */
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cmpl %ecx,%edx
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setaeb ovfl_flag /* Keep a record */
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jb L_no_adjust
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subl %ecx,%edx /* Prevent the overflow */
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L_no_adjust:
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/* Divide the 64 bit number by the 32 bit denominator */
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divl %ecx
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movl %eax,result_2
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/* Work on the remainder of the first division */
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xorl %eax,%eax
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divl %ecx
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movl %eax,result_1
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/* Work on the remainder of the 64 bit division */
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xorl %eax,%eax
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divl %ecx
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testb $255,ovfl_flag /* was the num > denom ? */
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je L_no_overflow
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/* Do the shifting here */
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/* increase the exponent */
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incl EXP(%edi)
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/* shift the mantissa right one bit */
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stc /* To set the ms bit */
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rcrl result_2
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rcrl result_1
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rcrl %eax
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L_no_overflow:
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jmp LRound_precision /* Do the rounding as required*/
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/*---------------------------------------------------------------------------+
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| Divide: Return arg1/arg2 to arg3. |
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| |
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| This routine does not use the exponents of arg1 and arg2, but does |
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| adjust the exponent of arg3. |
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| |
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| The maximum returned value is (ignoring exponents) |
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| .ffffffff ffffffff |
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| ------------------ = 1.ffffffff fffffffe |
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| .80000000 00000000 |
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| and the minimum is |
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| .80000000 00000000 |
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| ------------------ = .80000000 00000001 (rounded) |
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| .ffffffff ffffffff |
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| |
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+---------------------------------------------------------------------------*/
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L_Full_Division:
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/* Save extended dividend in local register*/
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movl SIGL(%esi),%eax
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movl %eax,accum_2
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movl SIGH(%esi),%eax
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movl %eax,accum_3
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xorl %eax,%eax
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movl %eax,accum_1 /* zero the extension */
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movl %eax,accum_0 /* zero the extension */
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movl SIGL(%esi),%eax /* Get the current num */
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movl SIGH(%esi),%edx
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/*----------------------------------------------------------------------*/
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/* Initialization done */
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/* Do the first 32 bits */
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movb $0,ovfl_flag
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cmpl SIGH(%ebx),%edx /* Test for imminent overflow */
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jb LLess_than_1
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ja LGreater_than_1
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cmpl SIGL(%ebx),%eax
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jb LLess_than_1
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LGreater_than_1:
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/* The dividend is greater or equal, would cause overflow */
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setaeb ovfl_flag /* Keep a record */
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subl SIGL(%ebx),%eax
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sbbl SIGH(%ebx),%edx /* Prevent the overflow */
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movl %eax,accum_2
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movl %edx,accum_3
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LLess_than_1:
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/* At this point, we have a dividend < divisor, with a record of
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adjustment in ovfl_flag */
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/* We will divide by a number which is too large */
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movl SIGH(%ebx),%ecx
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addl $1,%ecx
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jnc LFirst_div_not_1
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/* here we need to divide by 100000000h,
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i.e., no division at all.. */
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mov %edx,%eax
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jmp LFirst_div_done
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LFirst_div_not_1:
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divl %ecx /* Divide the numerator by the augmented
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denom ms dw */
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LFirst_div_done:
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movl %eax,result_2 /* Put the result in the answer */
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mull SIGH(%ebx) /* mul by the ms dw of the denom */
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subl %eax,accum_2 /* Subtract from the num local reg */
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sbbl %edx,accum_3
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movl result_2,%eax /* Get the result back */
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mull SIGL(%ebx) /* now mul the ls dw of the denom */
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subl %eax,accum_1 /* Subtract from the num local reg */
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sbbl %edx,accum_2
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sbbl $0,accum_3
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je LDo_2nd_32_bits /* Must check for non-zero result here */
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#ifdef PARANOID
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jb L_bugged_1
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#endif PARANOID
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/* need to subtract another once of the denom */
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incl result_2 /* Correct the answer */
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movl SIGL(%ebx),%eax
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movl SIGH(%ebx),%edx
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subl %eax,accum_1 /* Subtract from the num local reg */
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sbbl %edx,accum_2
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#ifdef PARANOID
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sbbl $0,accum_3
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jne L_bugged_1 /* Must check for non-zero result here */
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#endif PARANOID
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/*----------------------------------------------------------------------*/
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/* Half of the main problem is done, there is just a reduced numerator
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to handle now */
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/* Work with the second 32 bits, accum_0 not used from now on */
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LDo_2nd_32_bits:
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movl accum_2,%edx /* get the reduced num */
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movl accum_1,%eax
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/* need to check for possible subsequent overflow */
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cmpl SIGH(%ebx),%edx
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jb LDo_2nd_div
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ja LPrevent_2nd_overflow
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cmpl SIGL(%ebx),%eax
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jb LDo_2nd_div
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LPrevent_2nd_overflow:
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/* The numerator is greater or equal, would cause overflow */
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/* prevent overflow */
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subl SIGL(%ebx),%eax
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sbbl SIGH(%ebx),%edx
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movl %edx,accum_2
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movl %eax,accum_1
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incl result_2 /* Reflect the subtraction in the answer */
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#ifdef PARANOID
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je L_bugged_2 /* Can't bump the result to 1.0 */
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#endif PARANOID
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LDo_2nd_div:
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cmpl $0,%ecx /* augmented denom msw*/
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jnz LSecond_div_not_1
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/* %ecx == 0, we are dividing by 1.0 */
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mov %edx,%eax
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jmp LSecond_div_done
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LSecond_div_not_1:
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divl %ecx /* Divide the numerator by the denom ms dw */
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LSecond_div_done:
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movl %eax,result_1 /* Put the result in the answer */
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mull SIGH(%ebx) /* mul by the ms dw of the denom */
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subl %eax,accum_1 /* Subtract from the num local reg */
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sbbl %edx,accum_2
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#ifdef PARANOID
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jc L_bugged_2
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#endif PARANOID
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movl result_1,%eax /* Get the result back */
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mull SIGL(%ebx) /* now mul the ls dw of the denom */
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subl %eax,accum_0 /* Subtract from the num local reg */
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sbbl %edx,accum_1 /* Subtract from the num local reg */
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sbbl $0,accum_2
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#ifdef PARANOID
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jc L_bugged_2
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#endif PARANOID
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jz LDo_3rd_32_bits
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#ifdef PARANOID
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cmpl $1,accum_2
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jne L_bugged_2
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#endif PARANOID
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/* need to subtract another once of the denom */
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movl SIGL(%ebx),%eax
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movl SIGH(%ebx),%edx
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subl %eax,accum_0 /* Subtract from the num local reg */
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sbbl %edx,accum_1
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sbbl $0,accum_2
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#ifdef PARANOID
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jc L_bugged_2
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jne L_bugged_2
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#endif PARANOID
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addl $1,result_1 /* Correct the answer */
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adcl $0,result_2
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#ifdef PARANOID
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jc L_bugged_2 /* Must check for non-zero result here */
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#endif PARANOID
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/*----------------------------------------------------------------------*/
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/* The division is essentially finished here, we just need to perform
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tidying operations. */
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/* deal with the 3rd 32 bits */
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LDo_3rd_32_bits:
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movl accum_1,%edx /* get the reduced num */
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movl accum_0,%eax
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/* need to check for possible subsequent overflow */
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cmpl SIGH(%ebx),%edx /* denom*/
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jb LRound_prep
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ja LPrevent_3rd_overflow
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cmpl SIGL(%ebx),%eax /* denom */
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jb LRound_prep
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LPrevent_3rd_overflow:
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/* prevent overflow */
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subl SIGL(%ebx),%eax
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sbbl SIGH(%ebx),%edx
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movl %edx,accum_1
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movl %eax,accum_0
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addl $1,result_1 /* Reflect the subtraction in the answer */
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adcl $0,result_2
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jne LRound_prep
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jnc LRound_prep
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/* This is a tricky spot, there is an overflow of the answer */
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movb $255,ovfl_flag /* Overflow -> 1.000 */
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LRound_prep:
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/* Prepare for rounding.
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// To test for rounding, we just need to compare 2*accum with the
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// denom. */
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movl accum_0,%ecx
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movl accum_1,%edx
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movl %ecx,%eax
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orl %edx,%eax
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jz LRound_ovfl /* The accumulator contains zero.*/
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/* Multiply by 2 */
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clc
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rcll $1,%ecx
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rcll $1,%edx
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jc LRound_large /* No need to compare, denom smaller */
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subl SIGL(%ebx),%ecx
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sbbl SIGH(%ebx),%edx
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jnc LRound_not_small
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movl $0x70000000,%eax /* Denom was larger */
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jmp LRound_ovfl
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LRound_not_small:
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jnz LRound_large
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movl $0x80000000,%eax /* Remainder was exactly 1/2 denom */
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jmp LRound_ovfl
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LRound_large:
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movl $0xff000000,%eax /* Denom was smaller */
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LRound_ovfl:
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/* We are now ready to deal with rounding, but first we must get
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the bits properly aligned */
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testb $255,ovfl_flag /* was the num > denom ? */
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je LRound_precision
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incl EXP(%edi)
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/* shift the mantissa right one bit */
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stc /* Will set the ms bit */
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rcrl result_2
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rcrl result_1
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rcrl %eax
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/* Round the result as required */
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LRound_precision:
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decl EXP(%edi) /* binary point between 1st & 2nd bits */
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movl %eax,%edx
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movl result_1,%ebx
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movl result_2,%eax
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jmp FPU_round
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#ifdef PARANOID
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/* The logic is wrong if we got here */
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L_bugged:
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pushl EX_INTERNAL|0x202
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call EXCEPTION
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pop %ebx
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jmp L_exit
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L_bugged_1:
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pushl EX_INTERNAL|0x203
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call EXCEPTION
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pop %ebx
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jmp L_exit
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L_bugged_2:
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pushl EX_INTERNAL|0x204
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call EXCEPTION
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pop %ebx
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jmp L_exit
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L_exit:
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popl %ebx
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popl %edi
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popl %esi
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leave
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ret
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#endif PARANOID
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