368 lines
9.9 KiB
ArmAsm
368 lines
9.9 KiB
ArmAsm
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/* SPDX-License-Identifier: GPL-2.0 */
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.file "div_Xsig.S"
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/*---------------------------------------------------------------------------+
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| div_Xsig.S |
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| Division subroutine for 96 bit quantities |
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| Copyright (C) 1994,1995 |
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| W. Metzenthen, 22 Parker St, Ormond, Vic 3163, |
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| Australia. E-mail billm@jacobi.maths.monash.edu.au |
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+---------------------------------------------------------------------------*/
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/*---------------------------------------------------------------------------+
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| Divide the 96 bit quantity pointed to by a, by that pointed to by b, and |
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| put the 96 bit result at the location d. |
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| The result may not be accurate to 96 bits. It is intended for use where |
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| a result better than 64 bits is required. The result should usually be |
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| good to at least 94 bits. |
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| The returned result is actually divided by one half. This is done to |
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| prevent overflow. |
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| .aaaaaaaaaaaaaa / .bbbbbbbbbbbbb -> .dddddddddddd |
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| void div_Xsig(Xsig *a, Xsig *b, Xsig *dest) |
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+---------------------------------------------------------------------------*/
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#include "exception.h"
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#include "fpu_emu.h"
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#define XsigLL(x) (x)
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#define XsigL(x) 4(x)
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#define XsigH(x) 8(x)
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#ifndef NON_REENTRANT_FPU
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/*
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Local storage on the stack:
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Accumulator: FPU_accum_3:FPU_accum_2:FPU_accum_1:FPU_accum_0
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*/
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#define FPU_accum_3 -4(%ebp)
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#define FPU_accum_2 -8(%ebp)
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#define FPU_accum_1 -12(%ebp)
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#define FPU_accum_0 -16(%ebp)
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#define FPU_result_3 -20(%ebp)
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#define FPU_result_2 -24(%ebp)
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#define FPU_result_1 -28(%ebp)
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#else
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.data
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/*
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Local storage in a static area:
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Accumulator: FPU_accum_3:FPU_accum_2:FPU_accum_1:FPU_accum_0
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*/
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.align 4,0
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FPU_accum_3:
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.long 0
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FPU_accum_2:
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.long 0
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FPU_accum_1:
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.long 0
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FPU_accum_0:
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.long 0
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FPU_result_3:
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.long 0
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FPU_result_2:
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.long 0
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FPU_result_1:
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.long 0
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#endif /* NON_REENTRANT_FPU */
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.text
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ENTRY(div_Xsig)
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pushl %ebp
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movl %esp,%ebp
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#ifndef NON_REENTRANT_FPU
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subl $28,%esp
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#endif /* NON_REENTRANT_FPU */
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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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#ifdef PARANOID
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testl $0x80000000, XsigH(%ebx) /* Divisor */
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je L_bugged
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#endif /* PARANOID */
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/*---------------------------------------------------------------------------+
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| Divide: Return arg1/arg2 to arg3. |
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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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/* Save extended dividend in local register */
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/* Divide by 2 to prevent overflow */
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clc
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movl XsigH(%esi),%eax
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rcrl %eax
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movl %eax,FPU_accum_3
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movl XsigL(%esi),%eax
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rcrl %eax
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movl %eax,FPU_accum_2
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movl XsigLL(%esi),%eax
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rcrl %eax
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movl %eax,FPU_accum_1
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movl $0,%eax
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rcrl %eax
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movl %eax,FPU_accum_0
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movl FPU_accum_2,%eax /* Get the current num */
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movl FPU_accum_3,%edx
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/*----------------------------------------------------------------------*/
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/* Initialization done.
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Do the first 32 bits. */
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/* We will divide by a number which is too large */
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movl XsigH(%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,FPU_result_3 /* Put the result in the answer */
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mull XsigH(%ebx) /* mul by the ms dw of the denom */
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subl %eax,FPU_accum_2 /* Subtract from the num local reg */
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sbbl %edx,FPU_accum_3
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movl FPU_result_3,%eax /* Get the result back */
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mull XsigL(%ebx) /* now mul the ls dw of the denom */
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subl %eax,FPU_accum_1 /* Subtract from the num local reg */
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sbbl %edx,FPU_accum_2
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sbbl $0,FPU_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 FPU_result_3 /* Correct the answer */
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movl XsigL(%ebx),%eax
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movl XsigH(%ebx),%edx
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subl %eax,FPU_accum_1 /* Subtract from the num local reg */
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sbbl %edx,FPU_accum_2
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#ifdef PARANOID
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sbbl $0,FPU_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, FPU_accum_0 not used from now on */
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LDo_2nd_32_bits:
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movl FPU_accum_2,%edx /* get the reduced num */
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movl FPU_accum_1,%eax
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/* need to check for possible subsequent overflow */
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cmpl XsigH(%ebx),%edx
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jb LDo_2nd_div
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ja LPrevent_2nd_overflow
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cmpl XsigL(%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 XsigL(%ebx),%eax
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sbbl XsigH(%ebx),%edx
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movl %edx,FPU_accum_2
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movl %eax,FPU_accum_1
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incl FPU_result_3 /* 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,FPU_result_2 /* Put the result in the answer */
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mull XsigH(%ebx) /* mul by the ms dw of the denom */
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subl %eax,FPU_accum_1 /* Subtract from the num local reg */
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sbbl %edx,FPU_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 FPU_result_2,%eax /* Get the result back */
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mull XsigL(%ebx) /* now mul the ls dw of the denom */
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subl %eax,FPU_accum_0 /* Subtract from the num local reg */
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sbbl %edx,FPU_accum_1 /* Subtract from the num local reg */
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sbbl $0,FPU_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,FPU_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 XsigL(%ebx),%eax
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movl XsigH(%ebx),%edx
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subl %eax,FPU_accum_0 /* Subtract from the num local reg */
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sbbl %edx,FPU_accum_1
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sbbl $0,FPU_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,FPU_result_2 /* Correct the answer */
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adcl $0,FPU_result_3
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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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/* We use an approximation for the third 32 bits.
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To take account of the 3rd 32 bits of the divisor
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(call them del), we subtract del * (a/b) */
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movl FPU_result_3,%eax /* a/b */
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mull XsigLL(%ebx) /* del */
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subl %edx,FPU_accum_1
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/* A borrow indicates that the result is negative */
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jnb LTest_over
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movl XsigH(%ebx),%edx
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addl %edx,FPU_accum_1
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subl $1,FPU_result_2 /* Adjust the answer */
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sbbl $0,FPU_result_3
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/* The above addition might not have been enough, check again. */
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movl FPU_accum_1,%edx /* get the reduced num */
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cmpl XsigH(%ebx),%edx /* denom */
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jb LDo_3rd_div
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movl XsigH(%ebx),%edx
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addl %edx,FPU_accum_1
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subl $1,FPU_result_2 /* Adjust the answer */
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sbbl $0,FPU_result_3
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jmp LDo_3rd_div
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LTest_over:
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movl FPU_accum_1,%edx /* get the reduced num */
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/* need to check for possible subsequent overflow */
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cmpl XsigH(%ebx),%edx /* denom */
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jb LDo_3rd_div
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/* prevent overflow */
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subl XsigH(%ebx),%edx
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movl %edx,FPU_accum_1
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addl $1,FPU_result_2 /* Reflect the subtraction in the answer */
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adcl $0,FPU_result_3
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LDo_3rd_div:
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movl FPU_accum_0,%eax
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movl FPU_accum_1,%edx
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divl XsigH(%ebx)
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movl %eax,FPU_result_1 /* Rough estimate of third word */
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movl PARAM3,%esi /* pointer to answer */
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movl FPU_result_1,%eax
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movl %eax,XsigLL(%esi)
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movl FPU_result_2,%eax
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movl %eax,XsigL(%esi)
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movl FPU_result_3,%eax
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movl %eax,XsigH(%esi)
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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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#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|0x240
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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|0x241
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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|0x242
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call EXCEPTION
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pop %ebx
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jmp L_exit
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#endif /* PARANOID */
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ENDPROC(div_Xsig)
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