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|
.file "div_Xsig.S"
/*---------------------------------------------------------------------------+
| div_Xsig.S |
| |
| Division subroutine for 96 bit quantities |
| |
| Copyright (C) 1994,1995 |
| W. Metzenthen, 22 Parker St, Ormond, Vic 3163, |
| Australia. E-mail billm@jacobi.maths.monash.edu.au |
| |
| |
+---------------------------------------------------------------------------*/
/*---------------------------------------------------------------------------+
| Divide the 96 bit quantity pointed to by a, by that pointed to by b, and |
| put the 96 bit result at the location d. |
| |
| The result may not be accurate to 96 bits. It is intended for use where |
| a result better than 64 bits is required. The result should usually be |
| good to at least 94 bits. |
| The returned result is actually divided by one half. This is done to |
| prevent overflow. |
| |
| .aaaaaaaaaaaaaa / .bbbbbbbbbbbbb -> .dddddddddddd |
| |
| void div_Xsig(Xsig *a, Xsig *b, Xsig *dest) |
| |
+---------------------------------------------------------------------------*/
#include "exception.h"
#include "fpu_emu.h"
#define XsigLL(x) (x)
#define XsigL(x) 4(x)
#define XsigH(x) 8(x)
#ifndef NON_REENTRANT_FPU
/*
Local storage on the stack:
Accumulator: FPU_accum_3:FPU_accum_2:FPU_accum_1:FPU_accum_0
*/
#define FPU_accum_3 -4(%ebp)
#define FPU_accum_2 -8(%ebp)
#define FPU_accum_1 -12(%ebp)
#define FPU_accum_0 -16(%ebp)
#define FPU_result_3 -20(%ebp)
#define FPU_result_2 -24(%ebp)
#define FPU_result_1 -28(%ebp)
#else
.data
/*
Local storage in a static area:
Accumulator: FPU_accum_3:FPU_accum_2:FPU_accum_1:FPU_accum_0
*/
.align 4,0
FPU_accum_3:
.long 0
FPU_accum_2:
.long 0
FPU_accum_1:
.long 0
FPU_accum_0:
.long 0
FPU_result_3:
.long 0
FPU_result_2:
.long 0
FPU_result_1:
.long 0
#endif /* NON_REENTRANT_FPU */
.text
ENTRY(div_Xsig)
pushl %ebp
movl %esp,%ebp
#ifndef NON_REENTRANT_FPU
subl $28,%esp
#endif /* NON_REENTRANT_FPU */
pushl %esi
pushl %edi
pushl %ebx
movl PARAM1,%esi /* pointer to num */
movl PARAM2,%ebx /* pointer to denom */
#ifdef PARANOID
testl $0x80000000, XsigH(%ebx) /* Divisor */
je L_bugged
#endif /* PARANOID */
/*---------------------------------------------------------------------------+
| Divide: Return arg1/arg2 to arg3. |
| |
| The maximum returned value is (ignoring exponents) |
| .ffffffff ffffffff |
| ------------------ = 1.ffffffff fffffffe |
| .80000000 00000000 |
| and the minimum is |
| .80000000 00000000 |
| ------------------ = .80000000 00000001 (rounded) |
| .ffffffff ffffffff |
| |
+---------------------------------------------------------------------------*/
/* Save extended dividend in local register */
/* Divide by 2 to prevent overflow */
clc
movl XsigH(%esi),%eax
rcrl %eax
movl %eax,FPU_accum_3
movl XsigL(%esi),%eax
rcrl %eax
movl %eax,FPU_accum_2
movl XsigLL(%esi),%eax
rcrl %eax
movl %eax,FPU_accum_1
movl $0,%eax
rcrl %eax
movl %eax,FPU_accum_0
movl FPU_accum_2,%eax /* Get the current num */
movl FPU_accum_3,%edx
/*----------------------------------------------------------------------*/
/* Initialization done.
Do the first 32 bits. */
/* We will divide by a number which is too large */
movl XsigH(%ebx),%ecx
addl $1,%ecx
jnc LFirst_div_not_1
/* here we need to divide by 100000000h,
i.e., no division at all.. */
mov %edx,%eax
jmp LFirst_div_done
LFirst_div_not_1:
divl %ecx /* Divide the numerator by the augmented
denom ms dw */
LFirst_div_done:
movl %eax,FPU_result_3 /* Put the result in the answer */
mull XsigH(%ebx) /* mul by the ms dw of the denom */
subl %eax,FPU_accum_2 /* Subtract from the num local reg */
sbbl %edx,FPU_accum_3
movl FPU_result_3,%eax /* Get the result back */
mull XsigL(%ebx) /* now mul the ls dw of the denom */
subl %eax,FPU_accum_1 /* Subtract from the num local reg */
sbbl %edx,FPU_accum_2
sbbl $0,FPU_accum_3
je LDo_2nd_32_bits /* Must check for non-zero result here */
#ifdef PARANOID
jb L_bugged_1
#endif /* PARANOID */
/* need to subtract another once of the denom */
incl FPU_result_3 /* Correct the answer */
movl XsigL(%ebx),%eax
movl XsigH(%ebx),%edx
subl %eax,FPU_accum_1 /* Subtract from the num local reg */
sbbl %edx,FPU_accum_2
#ifdef PARANOID
sbbl $0,FPU_accum_3
jne L_bugged_1 /* Must check for non-zero result here */
#endif /* PARANOID */
/*----------------------------------------------------------------------*/
/* Half of the main problem is done, there is just a reduced numerator
to handle now.
Work with the second 32 bits, FPU_accum_0 not used from now on */
LDo_2nd_32_bits:
movl FPU_accum_2,%edx /* get the reduced num */
movl FPU_accum_1,%eax
/* need to check for possible subsequent overflow */
cmpl XsigH(%ebx),%edx
jb LDo_2nd_div
ja LPrevent_2nd_overflow
cmpl XsigL(%ebx),%eax
jb LDo_2nd_div
LPrevent_2nd_overflow:
/* The numerator is greater or equal, would cause overflow */
/* prevent overflow */
subl XsigL(%ebx),%eax
sbbl XsigH(%ebx),%edx
movl %edx,FPU_accum_2
movl %eax,FPU_accum_1
incl FPU_result_3 /* Reflect the subtraction in the answer */
#ifdef PARANOID
je L_bugged_2 /* Can't bump the result to 1.0 */
#endif /* PARANOID */
LDo_2nd_div:
cmpl $0,%ecx /* augmented denom msw */
jnz LSecond_div_not_1
/* %ecx == 0, we are dividing by 1.0 */
mov %edx,%eax
jmp LSecond_div_done
LSecond_div_not_1:
divl %ecx /* Divide the numerator by the denom ms dw */
LSecond_div_done:
movl %eax,FPU_result_2 /* Put the result in the answer */
mull XsigH(%ebx) /* mul by the ms dw of the denom */
subl %eax,FPU_accum_1 /* Subtract from the num local reg */
sbbl %edx,FPU_accum_2
#ifdef PARANOID
jc L_bugged_2
#endif /* PARANOID */
movl FPU_result_2,%eax /* Get the result back */
mull XsigL(%ebx) /* now mul the ls dw of the denom */
subl %eax,FPU_accum_0 /* Subtract from the num local reg */
sbbl %edx,FPU_accum_1 /* Subtract from the num local reg */
sbbl $0,FPU_accum_2
#ifdef PARANOID
jc L_bugged_2
#endif /* PARANOID */
jz LDo_3rd_32_bits
#ifdef PARANOID
cmpl $1,FPU_accum_2
jne L_bugged_2
#endif /* PARANOID */
/* need to subtract another once of the denom */
movl XsigL(%ebx),%eax
movl XsigH(%ebx),%edx
subl %eax,FPU_accum_0 /* Subtract from the num local reg */
sbbl %edx,FPU_accum_1
sbbl $0,FPU_accum_2
#ifdef PARANOID
jc L_bugged_2
jne L_bugged_2
#endif /* PARANOID */
addl $1,FPU_result_2 /* Correct the answer */
adcl $0,FPU_result_3
#ifdef PARANOID
jc L_bugged_2 /* Must check for non-zero result here */
#endif /* PARANOID */
/*----------------------------------------------------------------------*/
/* The division is essentially finished here, we just need to perform
tidying operations.
Deal with the 3rd 32 bits */
LDo_3rd_32_bits:
/* We use an approximation for the third 32 bits.
To take account of the 3rd 32 bits of the divisor
(call them del), we subtract del * (a/b) */
movl FPU_result_3,%eax /* a/b */
mull XsigLL(%ebx) /* del */
subl %edx,FPU_accum_1
/* A borrow indicates that the result is negative */
jnb LTest_over
movl XsigH(%ebx),%edx
addl %edx,FPU_accum_1
subl $1,FPU_result_2 /* Adjust the answer */
sbbl $0,FPU_result_3
/* The above addition might not have been enough, check again. */
movl FPU_accum_1,%edx /* get the reduced num */
cmpl XsigH(%ebx),%edx /* denom */
jb LDo_3rd_div
movl XsigH(%ebx),%edx
addl %edx,FPU_accum_1
subl $1,FPU_result_2 /* Adjust the answer */
sbbl $0,FPU_result_3
jmp LDo_3rd_div
LTest_over:
movl FPU_accum_1,%edx /* get the reduced num */
/* need to check for possible subsequent overflow */
cmpl XsigH(%ebx),%edx /* denom */
jb LDo_3rd_div
/* prevent overflow */
subl XsigH(%ebx),%edx
movl %edx,FPU_accum_1
addl $1,FPU_result_2 /* Reflect the subtraction in the answer */
adcl $0,FPU_result_3
LDo_3rd_div:
movl FPU_accum_0,%eax
movl FPU_accum_1,%edx
divl XsigH(%ebx)
movl %eax,FPU_result_1 /* Rough estimate of third word */
movl PARAM3,%esi /* pointer to answer */
movl FPU_result_1,%eax
movl %eax,XsigLL(%esi)
movl FPU_result_2,%eax
movl %eax,XsigL(%esi)
movl FPU_result_3,%eax
movl %eax,XsigH(%esi)
L_exit:
popl %ebx
popl %edi
popl %esi
leave
ret
#ifdef PARANOID
/* The logic is wrong if we got here */
L_bugged:
pushl EX_INTERNAL|0x240
call EXCEPTION
pop %ebx
jmp L_exit
L_bugged_1:
pushl EX_INTERNAL|0x241
call EXCEPTION
pop %ebx
jmp L_exit
L_bugged_2:
pushl EX_INTERNAL|0x242
call EXCEPTION
pop %ebx
jmp L_exit
#endif /* PARANOID */
ENDPROC(div_Xsig)
|
