reg_u_div.S 12.1 KB
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/* SPDX-License-Identifier: GPL-2.0 */
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	.file	"reg_u_div.S"
/*---------------------------------------------------------------------------+
 |  reg_u_div.S                                                              |
 |                                                                           |
 | Divide one FPU_REG by another and put the result in a destination FPU_REG.|
 |                                                                           |
 | Copyright (C) 1992,1993,1995,1997                                         |
 |                  W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
 |                  E-mail   billm@suburbia.net                              |
 |                                                                           |
 |                                                                           |
 +---------------------------------------------------------------------------*/

/*---------------------------------------------------------------------------+
 | Call from C as:                                                           |
 |    int FPU_u_div(FPU_REG *a, FPU_REG *b, FPU_REG *dest,                   |
 |                unsigned int control_word, char *sign)                     |
 |                                                                           |
 |  Does not compute the destination exponent, but does adjust it.           |
 |                                                                           |
 |    Return value is the tag of the answer, or-ed with FPU_Exception if     |
 |    one was raised, or -1 on internal error.                               |
 +---------------------------------------------------------------------------*/

#include "exception.h"
#include "fpu_emu.h"
#include "control_w.h"


/* #define	dSIGL(x)	(x) */
/* #define	dSIGH(x)	4(x) */


#ifndef NON_REENTRANT_FPU
/*
	Local storage on the stack:
	Result:		FPU_accum_3:FPU_accum_2:FPU_accum_1:FPU_accum_0
	Overflow flag:	ovfl_flag
 */
#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_1	-20(%ebp)
#define FPU_result_2	-24(%ebp)
#define FPU_ovfl_flag	-28(%ebp)

#else
.data
/*
	Local storage in a static area:
	Result:		FPU_accum_3:FPU_accum_2:FPU_accum_1:FPU_accum_0
	Overflow flag:	ovfl_flag
 */
	.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_1:
	.long	0
FPU_result_2:
	.long	0
FPU_ovfl_flag:
	.byte	0
#endif /* NON_REENTRANT_FPU */

#define REGA	PARAM1
#define REGB	PARAM2
#define DEST	PARAM3

.text
ENTRY(FPU_u_div)
	pushl	%ebp
	movl	%esp,%ebp
#ifndef NON_REENTRANT_FPU
	subl	$28,%esp
#endif /* NON_REENTRANT_FPU */

	pushl	%esi
	pushl	%edi
	pushl	%ebx

	movl	REGA,%esi
	movl	REGB,%ebx
	movl	DEST,%edi

	movswl	EXP(%esi),%edx
	movswl	EXP(%ebx),%eax
	subl	%eax,%edx
	addl	EXP_BIAS,%edx

	/* A denormal and a large number can cause an exponent underflow */
	cmpl	EXP_WAY_UNDER,%edx
	jg	xExp_not_underflow

	/* Set to a really low value allow correct handling */
	movl	EXP_WAY_UNDER,%edx

xExp_not_underflow:

	movw    %dx,EXP(%edi)

#ifdef PARANOID
/*	testl	$0x80000000, SIGH(%esi)	// Dividend */
/*	je	L_bugged */
	testl	$0x80000000, SIGH(%ebx)	/* Divisor */
	je	L_bugged
#endif /* PARANOID */ 

/* Check if the divisor can be treated as having just 32 bits */
	cmpl	$0,SIGL(%ebx)
	jnz	L_Full_Division	/* Can't do a quick divide */

/* We should be able to zip through the division here */
	movl	SIGH(%ebx),%ecx	/* The divisor */
	movl	SIGH(%esi),%edx	/* Dividend */
	movl	SIGL(%esi),%eax	/* Dividend */

	cmpl	%ecx,%edx
	setaeb	FPU_ovfl_flag	/* Keep a record */
	jb	L_no_adjust

	subl	%ecx,%edx	/* Prevent the overflow */

L_no_adjust:
	/* Divide the 64 bit number by the 32 bit denominator */
	divl	%ecx
	movl	%eax,FPU_result_2

	/* Work on the remainder of the first division */
	xorl	%eax,%eax
	divl	%ecx
	movl	%eax,FPU_result_1

	/* Work on the remainder of the 64 bit division */
	xorl	%eax,%eax
	divl	%ecx

	testb	$255,FPU_ovfl_flag	/* was the num > denom ? */
	je	L_no_overflow

	/* Do the shifting here */
	/* increase the exponent */
	incw	EXP(%edi)

	/* shift the mantissa right one bit */
	stc			/* To set the ms bit */
	rcrl	FPU_result_2
	rcrl	FPU_result_1
	rcrl	%eax

L_no_overflow:
	jmp	LRound_precision	/* Do the rounding as required */


/*---------------------------------------------------------------------------+
 |  Divide:   Return  arg1/arg2 to arg3.                                     |
 |                                                                           |
 |  This routine does not use the exponents of arg1 and arg2, but does       |
 |  adjust the exponent of 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                                          |
 |                                                                           |
 +---------------------------------------------------------------------------*/


L_Full_Division:
	/* Save extended dividend in local register */
	movl	SIGL(%esi),%eax
	movl	%eax,FPU_accum_2
	movl	SIGH(%esi),%eax
	movl	%eax,FPU_accum_3
	xorl	%eax,%eax
	movl	%eax,FPU_accum_1	/* zero the extension */
	movl	%eax,FPU_accum_0	/* zero the extension */

	movl	SIGL(%esi),%eax	/* Get the current num */
	movl	SIGH(%esi),%edx

/*----------------------------------------------------------------------*/
/* Initialization done.
   Do the first 32 bits. */

	movb	$0,FPU_ovfl_flag
	cmpl	SIGH(%ebx),%edx	/* Test for imminent overflow */
	jb	LLess_than_1
	ja	LGreater_than_1

	cmpl	SIGL(%ebx),%eax
	jb	LLess_than_1

LGreater_than_1:
/* The dividend is greater or equal, would cause overflow */
	setaeb	FPU_ovfl_flag		/* Keep a record */

	subl	SIGL(%ebx),%eax
	sbbl	SIGH(%ebx),%edx	/* Prevent the overflow */
	movl	%eax,FPU_accum_2
	movl	%edx,FPU_accum_3

LLess_than_1:
/* At this point, we have a dividend < divisor, with a record of
   adjustment in FPU_ovfl_flag */

	/* We will divide by a number which is too large */
	movl	SIGH(%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_2	/* Put the result in the answer */

	mull	SIGH(%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_2,%eax	/* Get the result back */
	mull	SIGL(%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_2	/* Correct the answer */

	movl	SIGL(%ebx),%eax
	movl	SIGH(%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	SIGH(%ebx),%edx
	jb	LDo_2nd_div
	ja	LPrevent_2nd_overflow

	cmpl	SIGL(%ebx),%eax
	jb	LDo_2nd_div

LPrevent_2nd_overflow:
/* The numerator is greater or equal, would cause overflow */
	/* prevent overflow */
	subl	SIGL(%ebx),%eax
	sbbl	SIGH(%ebx),%edx
	movl	%edx,FPU_accum_2
	movl	%eax,FPU_accum_1

	incl	FPU_result_2	/* 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_1	/* Put the result in the answer */

	mull	SIGH(%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_1,%eax	/* Get the result back */
	mull	SIGL(%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	SIGL(%ebx),%eax
	movl	SIGH(%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_1	/* Correct the answer */
	adcl	$0,FPU_result_2

#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:
	movl	FPU_accum_1,%edx		/* get the reduced num */
	movl	FPU_accum_0,%eax

	/* need to check for possible subsequent overflow */
	cmpl	SIGH(%ebx),%edx	/* denom */
	jb	LRound_prep
	ja	LPrevent_3rd_overflow

	cmpl	SIGL(%ebx),%eax	/* denom */
	jb	LRound_prep

LPrevent_3rd_overflow:
	/* prevent overflow */
	subl	SIGL(%ebx),%eax
	sbbl	SIGH(%ebx),%edx
	movl	%edx,FPU_accum_1
	movl	%eax,FPU_accum_0

	addl	$1,FPU_result_1	/* Reflect the subtraction in the answer */
	adcl	$0,FPU_result_2
	jne	LRound_prep
	jnc	LRound_prep

	/* This is a tricky spot, there is an overflow of the answer */
	movb	$255,FPU_ovfl_flag		/* Overflow -> 1.000 */

LRound_prep:
/*
 * Prepare for rounding.
 * To test for rounding, we just need to compare 2*accum with the
 * denom.
 */
	movl	FPU_accum_0,%ecx
	movl	FPU_accum_1,%edx
	movl	%ecx,%eax
	orl	%edx,%eax
	jz	LRound_ovfl		/* The accumulator contains zero. */

	/* Multiply by 2 */
	clc
	rcll	$1,%ecx
	rcll	$1,%edx
	jc	LRound_large		/* No need to compare, denom smaller */

	subl	SIGL(%ebx),%ecx
	sbbl	SIGH(%ebx),%edx
	jnc	LRound_not_small

	movl	$0x70000000,%eax	/* Denom was larger */
	jmp	LRound_ovfl

LRound_not_small:
	jnz	LRound_large

	movl	$0x80000000,%eax	/* Remainder was exactly 1/2 denom */
	jmp	LRound_ovfl

LRound_large:
	movl	$0xff000000,%eax	/* Denom was smaller */

LRound_ovfl:
/* We are now ready to deal with rounding, but first we must get
   the bits properly aligned */
	testb	$255,FPU_ovfl_flag	/* was the num > denom ? */
	je	LRound_precision

	incw	EXP(%edi)

	/* shift the mantissa right one bit */
	stc			/* Will set the ms bit */
	rcrl	FPU_result_2
	rcrl	FPU_result_1
	rcrl	%eax

/* Round the result as required */
LRound_precision:
	decw	EXP(%edi)	/* binary point between 1st & 2nd bits */

	movl	%eax,%edx
	movl	FPU_result_1,%ebx
	movl	FPU_result_2,%eax
	jmp	fpu_reg_round


#ifdef PARANOID
/* The logic is wrong if we got here */
L_bugged:
	pushl	EX_INTERNAL|0x202
	call	EXCEPTION
	pop	%ebx
	jmp	L_exit

L_bugged_1:
	pushl	EX_INTERNAL|0x203
	call	EXCEPTION
	pop	%ebx
	jmp	L_exit

L_bugged_2:
	pushl	EX_INTERNAL|0x204
	call	EXCEPTION
	pop	%ebx
	jmp	L_exit

L_exit:
	movl	$-1,%eax
	popl	%ebx
	popl	%edi
	popl	%esi

	leave
	ret
#endif /* PARANOID */ 
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ENDPROC(FPU_u_div)