|
  |	scale.sa 3.3 7/30/91
  |
  |	The entry point sSCALE computes the destination operand
  |	scaled by the source operand.  If the absolute value of
  |	the source operand is (>= 2^14) an overflow or underflow
  |	is returned.
  |
  |	The entry point sscale is called from do_func to emulate
  |	the fscale unimplemented instruction.
  |
  |	Input: Double-extended destination operand in FPTEMP,
  |		double-extended source operand in ETEMP.
  |
  |	Output: The function returns scale(X,Y) to fp0.
  |
  |	Modifies: fp0.
  |
  |	Algorithm:
  |
  |		Copyright (C) Motorola, Inc. 1990
  |			All Rights Reserved
  |
  |       For details on the license for this file, please see the
  |       file, README, in this same directory.
  
  |SCALE    idnt    2,1 | Motorola 040 Floating Point Software Package
  
  	|section	8
  
  #include "fpsp.h"
  
  	|xref	t_ovfl2
  	|xref	t_unfl
  	|xref	round
  	|xref	t_resdnrm
  
  SRC_BNDS: .short	0x3fff,0x400c
  
  |
  | This entry point is used by the unimplemented instruction exception
  | handler.
  |
  |
  |
  |	FSCALE
  |
  	.global	sscale
  sscale:
  	fmovel		#0,%fpcr		|clr user enabled exc
  	clrl		%d1
  	movew		FPTEMP(%a6),%d1	|get dest exponent
  	smi		L_SCR1(%a6)	|use L_SCR1 to hold sign
  	andil		#0x7fff,%d1	|strip sign
  	movew		ETEMP(%a6),%d0	|check src bounds
  	andiw		#0x7fff,%d0	|clr sign bit
  	cmp2w		SRC_BNDS,%d0
  	bccs		src_in
  	cmpiw		#0x400c,%d0	|test for too large
  	bge		src_out
  |
  | The source input is below 1, so we check for denormalized numbers
  | and set unfl.
  |
  src_small:
  	moveb		DTAG(%a6),%d0
  	andib		#0xe0,%d0
  	tstb		%d0
  	beqs		no_denorm
  	st		STORE_FLG(%a6)	|dest already contains result
  	orl		#unfl_mask,USER_FPSR(%a6) |set UNFL
  den_done:
  	leal		FPTEMP(%a6),%a0
  	bra		t_resdnrm
  no_denorm:
  	fmovel		USER_FPCR(%a6),%FPCR
  	fmovex		FPTEMP(%a6),%fp0	|simply return dest
  	rts
  
  
  |
  | Source is within 2^14 range.  To perform the int operation,
  | move it to d0.
  |
  src_in:
  	fmovex		ETEMP(%a6),%fp0	|move in src for int
  	fmovel		#rz_mode,%fpcr	|force rz for src conversion
  	fmovel		%fp0,%d0		|int src to d0
  	fmovel		#0,%FPSR		|clr status from above
  	tstw		ETEMP(%a6)	|check src sign
  	blt		src_neg
  |
  | Source is positive.  Add the src to the dest exponent.
  | The result can be denormalized, if src = 0, or overflow,
  | if the result of the add sets a bit in the upper word.
  |
  src_pos:
  	tstw		%d1		|check for denorm
  	beq		dst_dnrm
  	addl		%d0,%d1		|add src to dest exp
  	beqs		denorm		|if zero, result is denorm
  	cmpil		#0x7fff,%d1	|test for overflow
  	bges		ovfl
  	tstb		L_SCR1(%a6)
  	beqs		spos_pos
  	orw		#0x8000,%d1
  spos_pos:
  	movew		%d1,FPTEMP(%a6)	|result in FPTEMP
  	fmovel		USER_FPCR(%a6),%FPCR
  	fmovex		FPTEMP(%a6),%fp0	|write result to fp0
  	rts
  ovfl:
  	tstb		L_SCR1(%a6)
  	beqs		sovl_pos
  	orw		#0x8000,%d1
  sovl_pos:
  	movew		FPTEMP(%a6),ETEMP(%a6)	|result in ETEMP
  	movel		FPTEMP_HI(%a6),ETEMP_HI(%a6)
  	movel		FPTEMP_LO(%a6),ETEMP_LO(%a6)
  	bra		t_ovfl2
  
  denorm:
  	tstb		L_SCR1(%a6)
  	beqs		den_pos
  	orw		#0x8000,%d1
  den_pos:
  	tstl		FPTEMP_HI(%a6)	|check j bit
  	blts		nden_exit	|if set, not denorm
  	movew		%d1,ETEMP(%a6)	|input expected in ETEMP
  	movel		FPTEMP_HI(%a6),ETEMP_HI(%a6)
  	movel		FPTEMP_LO(%a6),ETEMP_LO(%a6)
  	orl		#unfl_bit,USER_FPSR(%a6)	|set unfl
  	leal		ETEMP(%a6),%a0
  	bra		t_resdnrm
  nden_exit:
  	movew		%d1,FPTEMP(%a6)	|result in FPTEMP
  	fmovel		USER_FPCR(%a6),%FPCR
  	fmovex		FPTEMP(%a6),%fp0	|write result to fp0
  	rts
  
  |
  | Source is negative.  Add the src to the dest exponent.
  | (The result exponent will be reduced).  The result can be
  | denormalized.
  |
  src_neg:
  	addl		%d0,%d1		|add src to dest
  	beqs		denorm		|if zero, result is denorm
  	blts		fix_dnrm	|if negative, result is
  |					;needing denormalization
  	tstb		L_SCR1(%a6)
  	beqs		sneg_pos
  	orw		#0x8000,%d1
  sneg_pos:
  	movew		%d1,FPTEMP(%a6)	|result in FPTEMP
  	fmovel		USER_FPCR(%a6),%FPCR
  	fmovex		FPTEMP(%a6),%fp0	|write result to fp0
  	rts
  
  
  |
  | The result exponent is below denorm value.  Test for catastrophic
  | underflow and force zero if true.  If not, try to shift the
  | mantissa right until a zero exponent exists.
  |
  fix_dnrm:
  	cmpiw		#0xffc0,%d1	|lower bound for normalization
  	blt		fix_unfl	|if lower, catastrophic unfl
  	movew		%d1,%d0		|use d0 for exp
  	movel		%d2,-(%a7)	|free d2 for norm
  	movel		FPTEMP_HI(%a6),%d1
  	movel		FPTEMP_LO(%a6),%d2
  	clrl		L_SCR2(%a6)
  fix_loop:
  	addw		#1,%d0		|drive d0 to 0
  	lsrl		#1,%d1		|while shifting the
  	roxrl		#1,%d2		|mantissa to the right
  	bccs		no_carry
  	st		L_SCR2(%a6)	|use L_SCR2 to capture inex
  no_carry:
  	tstw		%d0		|it is finished when
  	blts		fix_loop	|d0 is zero or the mantissa
  	tstb		L_SCR2(%a6)
  	beqs		tst_zero
  	orl		#unfl_inx_mask,USER_FPSR(%a6)
  |					;set unfl, aunfl, ainex
  |
  | Test for zero. If zero, simply use fmove to return +/- zero
  | to the fpu.
  |
  tst_zero:
  	clrw		FPTEMP_EX(%a6)
  	tstb		L_SCR1(%a6)	|test for sign
  	beqs		tst_con
  	orw		#0x8000,FPTEMP_EX(%a6) |set sign bit
  tst_con:
  	movel		%d1,FPTEMP_HI(%a6)
  	movel		%d2,FPTEMP_LO(%a6)
  	movel		(%a7)+,%d2
  	tstl		%d1
  	bnes		not_zero
  	tstl		FPTEMP_LO(%a6)
  	bnes		not_zero
  |
  | Result is zero.  Check for rounding mode to set lsb.  If the
  | mode is rp, and the zero is positive, return smallest denorm.
  | If the mode is rm, and the zero is negative, return smallest
  | negative denorm.
  |
  	btstb		#5,FPCR_MODE(%a6) |test if rm or rp
  	beqs		no_dir
  	btstb		#4,FPCR_MODE(%a6) |check which one
  	beqs		zer_rm
  zer_rp:
  	tstb		L_SCR1(%a6)	|check sign
  	bnes		no_dir		|if set, neg op, no inc
  	movel		#1,FPTEMP_LO(%a6) |set lsb
  	bras		sm_dnrm
  zer_rm:
  	tstb		L_SCR1(%a6)	|check sign
  	beqs		no_dir		|if clr, neg op, no inc
  	movel		#1,FPTEMP_LO(%a6) |set lsb
  	orl		#neg_mask,USER_FPSR(%a6) |set N
  	bras		sm_dnrm
  no_dir:
  	fmovel		USER_FPCR(%a6),%FPCR
  	fmovex		FPTEMP(%a6),%fp0	|use fmove to set cc's
  	rts
  
  |
  | The rounding mode changed the zero to a smallest denorm. Call
  | t_resdnrm with exceptional operand in ETEMP.
  |
  sm_dnrm:
  	movel		FPTEMP_EX(%a6),ETEMP_EX(%a6)
  	movel		FPTEMP_HI(%a6),ETEMP_HI(%a6)
  	movel		FPTEMP_LO(%a6),ETEMP_LO(%a6)
  	leal		ETEMP(%a6),%a0
  	bra		t_resdnrm
  
  |
  | Result is still denormalized.
  |
  not_zero:
  	orl		#unfl_mask,USER_FPSR(%a6) |set unfl
  	tstb		L_SCR1(%a6)	|check for sign
  	beqs		fix_exit
  	orl		#neg_mask,USER_FPSR(%a6) |set N
  fix_exit:
  	bras		sm_dnrm
  
  
  |
  | The result has underflowed to zero. Return zero and set
  | unfl, aunfl, and ainex.
  |
  fix_unfl:
  	orl		#unfl_inx_mask,USER_FPSR(%a6)
  	btstb		#5,FPCR_MODE(%a6) |test if rm or rp
  	beqs		no_dir2
  	btstb		#4,FPCR_MODE(%a6) |check which one
  	beqs		zer_rm2
  zer_rp2:
  	tstb		L_SCR1(%a6)	|check sign
  	bnes		no_dir2		|if set, neg op, no inc
  	clrl		FPTEMP_EX(%a6)
  	clrl		FPTEMP_HI(%a6)
  	movel		#1,FPTEMP_LO(%a6) |set lsb
  	bras		sm_dnrm		|return smallest denorm
  zer_rm2:
  	tstb		L_SCR1(%a6)	|check sign
  	beqs		no_dir2		|if clr, neg op, no inc
  	movew		#0x8000,FPTEMP_EX(%a6)
  	clrl		FPTEMP_HI(%a6)
  	movel		#1,FPTEMP_LO(%a6) |set lsb
  	orl		#neg_mask,USER_FPSR(%a6) |set N
  	bra		sm_dnrm		|return smallest denorm
  
  no_dir2:
  	tstb		L_SCR1(%a6)
  	bges		pos_zero
  neg_zero:
  	clrl		FP_SCR1(%a6)	|clear the exceptional operand
  	clrl		FP_SCR1+4(%a6)	|for gen_except.
  	clrl		FP_SCR1+8(%a6)
  	fmoves		#0x80000000,%fp0
  	rts
  pos_zero:
  	clrl		FP_SCR1(%a6)	|clear the exceptional operand
  	clrl		FP_SCR1+4(%a6)	|for gen_except.
  	clrl		FP_SCR1+8(%a6)
  	fmoves		#0x00000000,%fp0
  	rts
  
  |
  | The destination is a denormalized number.  It must be handled
  | by first shifting the bits in the mantissa until it is normalized,
  | then adding the remainder of the source to the exponent.
  |
  dst_dnrm:
  	moveml		%d2/%d3,-(%a7)
  	movew		FPTEMP_EX(%a6),%d1
  	movel		FPTEMP_HI(%a6),%d2
  	movel		FPTEMP_LO(%a6),%d3
  dst_loop:
  	tstl		%d2		|test for normalized result
  	blts		dst_norm	|exit loop if so
  	tstl		%d0		|otherwise, test shift count
  	beqs		dst_fin		|if zero, shifting is done
  	subil		#1,%d0		|dec src
  	lsll		#1,%d3
  	roxll		#1,%d2
  	bras		dst_loop
  |
  | Destination became normalized.  Simply add the remaining
  | portion of the src to the exponent.
  |
  dst_norm:
  	addw		%d0,%d1		|dst is normalized; add src
  	tstb		L_SCR1(%a6)
  	beqs		dnrm_pos
  	orl		#0x8000,%d1
  dnrm_pos:
  	movemw		%d1,FPTEMP_EX(%a6)
  	moveml		%d2,FPTEMP_HI(%a6)
  	moveml		%d3,FPTEMP_LO(%a6)
  	fmovel		USER_FPCR(%a6),%FPCR
  	fmovex		FPTEMP(%a6),%fp0
  	moveml		(%a7)+,%d2/%d3
  	rts
  
  |
  | Destination remained denormalized.  Call t_excdnrm with
  | exceptional operand in ETEMP.
  |
  dst_fin:
  	tstb		L_SCR1(%a6)	|check for sign
  	beqs		dst_exit
  	orl		#neg_mask,USER_FPSR(%a6) |set N
  	orl		#0x8000,%d1
  dst_exit:
  	movemw		%d1,ETEMP_EX(%a6)
  	moveml		%d2,ETEMP_HI(%a6)
  	moveml		%d3,ETEMP_LO(%a6)
  	orl		#unfl_mask,USER_FPSR(%a6) |set unfl
  	moveml		(%a7)+,%d2/%d3
  	leal		ETEMP(%a6),%a0
  	bra		t_resdnrm
  
  |
  | Source is outside of 2^14 range.  Test the sign and branch
  | to the appropriate exception handler.
  |
  src_out:
  	tstb		L_SCR1(%a6)
  	beqs		scro_pos
  	orl		#0x8000,%d1
  scro_pos:
  	movel		FPTEMP_HI(%a6),ETEMP_HI(%a6)
  	movel		FPTEMP_LO(%a6),ETEMP_LO(%a6)
  	tstw		ETEMP(%a6)
  	blts		res_neg
  res_pos:
  	movew		%d1,ETEMP(%a6)	|result in ETEMP
  	bra		t_ovfl2
  res_neg:
  	movew		%d1,ETEMP(%a6)	|result in ETEMP
  	leal		ETEMP(%a6),%a0
  	bra		t_unfl
  	|end