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367 lines
9.9 KiB
367 lines
9.9 KiB
/* 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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| | |
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| Division subroutine for 96 bit quantities | |
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| | |
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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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/*---------------------------------------------------------------------------+ |
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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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| | |
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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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| | |
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| .aaaaaaaaaaaaaa / .bbbbbbbbbbbbb -> .dddddddddddd | |
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| | |
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| void div_Xsig(Xsig *a, Xsig *b, Xsig *dest) | |
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| | |
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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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SYM_FUNC_START(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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| | |
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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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/* 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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SYM_FUNC_END(div_Xsig)
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