reg_norm.s

LINUX 1.0 内核c源代码

/*---------------------------------------------------------------------------+
 |  reg_norm.S                                                               |
 |                                                                           |
 | Copyright (C) 1992,1993,1994                                              |
 |                       W. Metzenthen, 22 Parker St, Ormond, Vic 3163,      |
 |                       Australia.  E-mail   [e-mail]    |
 |                                                                           |
 | Normalize the value in a FPU_REG.                                         |
 |                                                                           |
 | Call from C as:                                                           |
 |   void normalize(FPU_REG *n)                                              |
 |                                                                           |
 |   void normalize_nuo(FPU_REG *n)                                          |
 |                                                                           |
 +---------------------------------------------------------------------------*/

#include "fpu_asm.h"


.text

	.align 2,144
.globl _normalize

_normalize:
	pushl	%ebp
	movl	%esp,%ebp
	pushl	%ebx

	movl	PARAM1,%ebx

#ifdef PARANOID
	cmpb	TW_Valid,TAG(%ebx)
	je	L_ok

	pushl	$0x220
	call	_exception
	addl	$4,%esp

L_ok:
#endif PARANOID

	movl	SIGH(%ebx),%edx
	movl	SIGL(%ebx),%eax

	orl	%edx,%edx	/* ms bits */
	js	L_done		/* Already normalized */
	jnz	L_shift_1	/* Shift left 1 - 31 bits */

	orl	%eax,%eax
	jz	L_zero		/* The contents are zero */

	movl	%eax,%edx
	xorl	%eax,%eax
	subl	$32,EXP(%ebx)	/* This can cause an underflow */

/* We need to shift left by 1 - 31 bits */
L_shift_1:
	bsrl	%edx,%ecx	/* get the required shift in %ecx */
	subl	$31,%ecx
	negl	%ecx
	shld	%cl,%eax,%edx
	shl	%cl,%eax
	subl	%ecx,EXP(%ebx)	/* This can cause an underflow */

	movl	%edx,SIGH(%ebx)
	movl	%eax,SIGL(%ebx)

L_done:
	cmpl	EXP_OVER,EXP(%ebx)
	jge	L_overflow

	cmpl	EXP_UNDER,EXP(%ebx)
	jle	L_underflow

L_exit:
	popl	%ebx
	leave
	ret


L_zero:
	movl	EXP_UNDER,EXP(%ebx)
	movb	TW_Zero,TAG(%ebx)
	jmp	L_exit

L_underflow:
	push	%ebx
	call	_arith_underflow
	pop	%ebx
	jmp	L_exit

L_overflow:
	push	%ebx
	call	_arith_overflow
	pop	%ebx
	jmp	L_exit



/* Normalise without reporting underflow or overflow */
	.align 2,144
.globl _normalize_nuo

_normalize_nuo:
	pushl	%ebp
	movl	%esp,%ebp
	pushl	%ebx

	movl	PARAM1,%ebx

#ifdef PARANOID
	cmpb	TW_Valid,TAG(%ebx)
	je	L_ok_nuo

	pushl	$0x221
	call	_exception
	addl	$4,%esp

L_ok_nuo:
#endif PARANOID

	movl	SIGH(%ebx),%edx
	movl	SIGL(%ebx),%eax

	orl	%edx,%edx	/* ms bits */
	js	L_exit		/* Already normalized */
	jnz	L_nuo_shift_1	/* Shift left 1 - 31 bits */

	orl	%eax,%eax
	jz	L_zero		/* The contents are zero */

	movl	%eax,%edx
	xorl	%eax,%eax
	subl	$32,EXP(%ebx)	/* This can cause an underflow */

/* We need to shift left by 1 - 31 bits */
L_nuo_shift_1:
	bsrl	%edx,%ecx	/* get the required shift in %ecx */
	subl	$31,%ecx
	negl	%ecx
	shld	%cl,%eax,%edx
	shl	%cl,%eax
	subl	%ecx,EXP(%ebx)	/* This can cause an underflow */

	movl	%edx,SIGH(%ebx)
	movl	%eax,SIGL(%ebx)
	jmp	L_exit