sgetem.s

RTEMS (Real-Time Executive for Multiprocessor Systems) is a free open source real-time operating sys

//
//      $Id: sgetem.S,v 1.1 1998/12/14 23:15:27 joel Exp $
//
//	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//	THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF MOTOROLA 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.defs"

	|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