sgetem.s

MIZI Research, Inc.发布的嵌入式Linux内核源码

|
|	sgetem.sa 3.1 12/10/90
|
|	The entry point sGETEXP returns the exponent portion 
|	of the input argument.  The exponent bias is removed
|	and the exponent value is returned as an extended 
|	precision number in fp0.  sGETEXPD handles denormalized
|	numbers.
|
|	The entry point sGETMAN extracts the mantissa of the 
|	input argument.  The mantissa is converted to an 
|	extended precision number and returned in fp0.  The
|	range of the result is [1.0 - 2.0).
|
|
|	Input:  Double-extended number X in the ETEMP space in
|		the floating-point save stack.
|
|	Output:	The functions return exp(X) or man(X) in fp0.
|
|	Modified: fp0.
|
|
|		Copyright (C) Motorola, Inc. 1990
|			All Rights Reserved
|
|	THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF MOTOROLA 
|	The copyright notice above does not evidence any  
|	actual or intended publication of such source code.

|SGETEM	idnt	2,1 | Motorola 040 Floating Point Software Package

	|section 8

	.include "fpsp.h"

	|xref	nrm_set

|
| This entry point is used by the unimplemented instruction exception
| handler.  It points a0 to the input operand.
|
|
|
|	SGETEXP
|

	.global	sgetexp
sgetexp:
	movew	LOCAL_EX(%a0),%d0	|get the exponent
	bclrl	#15,%d0		|clear the sign bit
	subw	#0x3fff,%d0	|subtract off the bias
	fmovew  %d0,%fp0		|move the exp to fp0
	rts

	.global	sgetexpd
sgetexpd:
	bclrb	#sign_bit,LOCAL_EX(%a0)
	bsr	nrm_set		|normalize (exp will go negative)
	movew	LOCAL_EX(%a0),%d0	|load resulting exponent into d0
	subw	#0x3fff,%d0	|subtract off the bias
	fmovew	%d0,%fp0		|move the exp to fp0
	rts
|
|
| This entry point is used by the unimplemented instruction exception
| handler.  It points a0 to the input operand.
|
|
|
|	SGETMAN
|
|
| For normalized numbers, leave the mantissa alone, simply load
| with an exponent of +/- $3fff.
|
	.global	sgetman
sgetman:
	movel	USER_FPCR(%a6),%d0
	andil	#0xffffff00,%d0	|clear rounding precision and mode
	fmovel	%d0,%fpcr		|this fpcr setting is used by the 882
	movew	LOCAL_EX(%a0),%d0	|get the exp (really just want sign bit)
	orw	#0x7fff,%d0	|clear old exp
	bclrl	#14,%d0	 	|make it the new exp +-3fff
	movew	%d0,LOCAL_EX(%a0)	|move the sign & exp back to fsave stack
	fmovex	(%a0),%fp0	|put new value back in fp0
	rts

|
| For denormalized numbers, shift the mantissa until the j-bit = 1,
| then load the exponent with +/1 $3fff.
|
	.global	sgetmand
sgetmand:
	movel	LOCAL_HI(%a0),%d0	|load ms mant in d0
	movel	LOCAL_LO(%a0),%d1	|load ls mant in d1
	bsr	shft		|shift mantissa bits till msbit is set
	movel	%d0,LOCAL_HI(%a0)	|put ms mant back on stack
	movel	%d1,LOCAL_LO(%a0)	|put ls mant back on stack
	bras	sgetman

|
|	SHFT
|
|	Shifts the mantissa bits until msbit is set.
|	input:
|		ms mantissa part in d0
|		ls mantissa part in d1
|	output:
|		shifted bits in d0 and d1
shft:
	tstl	%d0		|if any bits set in ms mant
	bnes	upper		|then branch
|				;else no bits set in ms mant
	tstl	%d1		|test if any bits set in ls mant
	bnes	cont		|if set then continue
	bras	shft_end	|else return
cont:
	movel	%d3,-(%a7)	|save d3
	exg	%d0,%d1		|shift ls mant to ms mant
	bfffo	%d0{#0:#32},%d3	|find first 1 in ls mant to d0
	lsll	%d3,%d0		|shift first 1 to integer bit in ms mant
	movel	(%a7)+,%d3	|restore d3
	bras	shft_end
upper:

	moveml	%d3/%d5/%d6,-(%a7)	|save registers
	bfffo	%d0{#0:#32},%d3	|find first 1 in ls mant to d0
	lsll	%d3,%d0		|shift ms mant until j-bit is set
	movel	%d1,%d6		|save ls mant in d6
	lsll	%d3,%d1		|shift ls mant by count
	movel	#32,%d5
	subl	%d3,%d5		|sub 32 from shift for ls mant
	lsrl	%d5,%d6		|shift off all bits but those that will
|				;be shifted into ms mant
	orl	%d6,%d0		|shift the ls mant bits into the ms mant
	moveml	(%a7)+,%d3/%d5/%d6	|restore registers
shft_end:
	rts

	|end