fp_util.s

讲述linux的初始化过程

	tst.b	(-3,%a0)		| to -inf
	jne	1b
	jra	5f
4:	tst.b	(-3,%a0)		| to +inf
	jeq	1b
5:	move.w	#0x407e,(-2,%a0)
	move.l	#0xffffff00,(%a0)+
	clr.l	(%a0)
	jra	2b
	| zero and denormalized
fp_ns_zero:
	tst.l	(%a0)+
	jne	1f
	tst.l	(%a0)
	jne	1f
	subq.l	#8,%a0
	printf	PNORM,"%p(",1,%a0
	printx	PNORM,%a0@
	printf	PNORM,")\n"
	rts				| zero.  nothing to do.
	| These are not merely subnormal numbers, but true denormals,
	| i.e. pathologically small (exponent is 2**-16383) numbers.
	| It is clearly impossible for even a normal extended number
	| with that exponent to fit into single precision, so just
	| write these ones off as "too darn small".
1:	fp_set_sr FPSR_EXC_UNFL		| Set UNFL bit
	clr.l	(%a0)
	clr.l	-(%a0)
	move.w	#0x3f81,-(%a0)		| i.e. 2**-126
	addq.l	#6,%a0
	moveq	#1,%d0
	jra	fp_ns_round		| round.
	| Infinities or NaNs
fp_ns_huge:
	subq.l	#4,%a0
	printf	PNORM,"%p(",1,%a0
	printx	PNORM,%a0@
	printf	PNORM,")\n"
	rts

	| fp_normalize_single_fast:
	| normalize an extended with single (23-bit) precision
	| this is only used by fsgldiv/fsgdlmul, where the
	| operand is not completly normalized.
	| args:	 %a0 (struct fp_ext *)

fp_normalize_single_fast:
	printf	PNORM,"nsf: %p(",1,%a0
	printx	PNORM,%a0@
	printf	PNORM,") "
	addq.l	#2,%a0
	move.w	(%a0)+,%d2
	cmp.w	#0x7fff,%d2
	jeq	fp_nsf_huge		| NaN / infinitive.
	move.l	(%a0)+,%d0		| get high lword of mantissa
fp_nsf_round:
	tst.l	(%a0)			| check the low lword
	jeq	1f
	| Set a sticky bit if it is non-zero.  This should only
	| affect the rounding in what would otherwise be equal-
	| distance situations, which is what we want it to do.
	bset	#0,%d0
1:	clr.l	(%a0)			| zap it from memory.
	| now, round off the low 8 bits of the hi lword.
	tst.b	%d0			| 8 low bits.
	jne	fp_nsf_checkround	| Are they non-zero?
	| nothing to do here
	subq.l	#8,%a0
	printf	PNORM,"%p(",1,%a0
	printx	PNORM,%a0@
	printf	PNORM,")\n"
	rts
fp_nsf_checkround:
	fp_set_sr FPSR_EXC_INEX2	| INEX2 bit
	clr.b	-(%a0)			| clear low byte of high lword
	subq.l	#3,%a0
	move.w	(FPD_RND,FPDATA),%d2	| rounding mode
	jne	2f			| %d2 == 0, round to nearest
	tst.b	%d0			| test guard bit
	jpl	9f			| zero is closer
	btst	#8,%d0			| test lsb bit
	| round to even behaviour, see above.
	jne	fp_nsf_doroundup		| round to infinity
	lsl.b	#1,%d0			| check low bits
	jeq	9f			| round to zero
fp_nsf_doroundup:
	| round (the mantissa, that is) towards infinity
	add.l	#0x100,(%a0)
	jcc	9f			| no overflow, good.
	| Overflow.  This means that the %d1 was 0xffffff00, so it
	| is now zero.  We will set the mantissa to reflect this, and
	| increment the exponent (checking for overflow there too)
	move.w	#0x8000,(%a0)
	addq.w	#1,-(%a0)
	cmp.w	#0x407f,(%a0)+		| exponent now overflown?
	jeq	fp_nsf_large		| yes, so make it infinity.
9:	subq.l	#4,%a0
	printf	PNORM,"%p(",1,%a0
	printx	PNORM,%a0@
	printf	PNORM,")\n"
	rts
	| check nondefault rounding modes
2:	subq.w	#2,%d2
	jcs	9b			| %d2 < 2, round to zero
	jhi	3f			| %d2 > 2, round to +infinity
	tst.b	(-3,%a0)		| to -inf
	jne	fp_nsf_doroundup	| negative, round to infinity
	jra	9b			| positive, round to zero
3:	tst.b	(-3,%a0)		| to +inf
	jeq	fp_nsf_doroundup		| positive, round to infinity
	jra	9b			| negative, round to zero
	| Exponent overflow.  Just call it infinity.
fp_nsf_large:
	tst.b	(3,%a0)
	jeq	1f
	fp_set_sr FPSR_EXC_INEX2
1:	fp_set_sr FPSR_EXC_OVFL
	move.w	(FPD_RND,FPDATA),%d2
	jne	3f			| %d2 = 0 round to nearest
1:	move.w	#0x7fff,(-2,%a0)
	clr.l	(%a0)+
	clr.l	(%a0)
2:	subq.l	#8,%a0
	printf	PNORM,"%p(",1,%a0
	printx	PNORM,%a0@
	printf	PNORM,")\n"
	rts
3:	subq.w	#2,%d2
	jcs	5f			| %d2 < 2, round to zero
	jhi	4f			| %d2 > 2, round to +infinity
	tst.b	(-3,%a0)		| to -inf
	jne	1b
	jra	5f
4:	tst.b	(-3,%a0)		| to +inf
	jeq	1b
5:	move.w	#0x407e,(-2,%a0)
	move.l	#0xffffff00,(%a0)+
	clr.l	(%a0)
	jra	2b
	| Infinities or NaNs
fp_nsf_huge:
	subq.l	#4,%a0
	printf	PNORM,"%p(",1,%a0
	printx	PNORM,%a0@
	printf	PNORM,")\n"
	rts

	| conv_ext2int (macro):
	| Generates a subroutine that converts an extended value to an
	| integer of a given size, again, with the appropriate type of
	| rounding.

	| Macro arguments:
	| s:	size, as given in an assembly instruction.
	| b:	number of bits in that size.

	| Subroutine arguments:
	| %a0:	source (struct fp_ext *)

	| Returns the integer in %d0 (like it should)

.macro conv_ext2int s,b
	.set	inf,(1<<(\b-1))-1	| i.e. MAXINT
	printf	PCONV,"e2i%d: %p(",2,#\b,%a0
	printx	PCONV,%a0@
	printf	PCONV,") "
	addq.l	#2,%a0
	move.w	(%a0)+,%d2		| exponent
	jeq	fp_e2i_zero\b		| zero / denorm (== 0, here)
	cmp.w	#0x7fff,%d2
	jeq	fp_e2i_huge\b		| Inf / NaN
	sub.w	#0x3ffe,%d2
	jcs	fp_e2i_small\b
	cmp.w	#\b,%d2
	jhi	fp_e2i_large\b
	move.l	(%a0),%d0
	move.l	%d0,%d1
	lsl.l	%d2,%d1
	jne	fp_e2i_round\b
	tst.l	(4,%a0)
	jne	fp_e2i_round\b
	neg.w	%d2
	add.w	#32,%d2
	lsr.l	%d2,%d0
9:	tst.w	(-4,%a0)
	jne	1f
	tst.\s	%d0
	jmi	fp_e2i_large\b
	printf	PCONV,"-> %p\n",1,%d0
	rts
1:	neg.\s	%d0
	jeq	1f
	jpl	fp_e2i_large\b
1:	printf	PCONV,"-> %p\n",1,%d0
	rts
fp_e2i_round\b:
	fp_set_sr FPSR_EXC_INEX2	| INEX2 bit
	neg.w	%d2
	add.w	#32,%d2
	.if	\b>16
	jeq	5f
	.endif
	lsr.l	%d2,%d0
	move.w	(FPD_RND,FPDATA),%d2	| rounding mode
	jne	2f			| %d2 == 0, round to nearest
	tst.l	%d1			| test guard bit
	jpl	9b			| zero is closer
	btst	%d2,%d0			| test lsb bit (%d2 still 0)
	jne	fp_e2i_doroundup\b
	lsl.l	#1,%d1			| check low bits
	jne	fp_e2i_doroundup\b
	tst.l	(4,%a0)
	jeq	9b
fp_e2i_doroundup\b:
	addq.l	#1,%d0
	jra	9b
	| check nondefault rounding modes
2:	subq.w	#2,%d2
	jcs	9b			| %d2 < 2, round to zero
	jhi	3f			| %d2 > 2, round to +infinity
	tst.w	(-4,%a0)		| to -inf
	jne	fp_e2i_doroundup\b	| negative, round to infinity
	jra	9b			| positive, round to zero
3:	tst.w	(-4,%a0)		| to +inf
	jeq	fp_e2i_doroundup\b	| positive, round to infinity
	jra	9b	| negative, round to zero
	| we are only want -2**127 get correctly rounded here,
	| since the guard bit is in the lower lword.
	| everything else ends up anyway as overflow.
	.if	\b>16
5:	move.w	(FPD_RND,FPDATA),%d2	| rounding mode
	jne	2b			| %d2 == 0, round to nearest
	move.l	(4,%a0),%d1		| test guard bit
	jpl	9b			| zero is closer
	lsl.l	#1,%d1			| check low bits
	jne	fp_e2i_doroundup\b
	jra	9b
	.endif
fp_e2i_zero\b:
	clr.l	%d0
	tst.l	(%a0)+
	jne	1f
	tst.l	(%a0)
	jeq	3f
1:	subq.l	#4,%a0
	fp_clr_sr FPSR_EXC_UNFL		| fp_normalize_ext has set this bit
fp_e2i_small\b:
	fp_set_sr FPSR_EXC_INEX2
	clr.l	%d0
	move.w	(FPD_RND,FPDATA),%d2	| rounding mode
	subq.w	#2,%d2
	jcs	3f			| %d2 < 2, round to nearest/zero
	jhi	2f			| %d2 > 2, round to +infinity
	tst.w	(-4,%a0)		| to -inf
	jeq	3f
	subq.\s	#1,%d0
	jra	3f
2:	tst.w	(-4,%a0)		| to +inf
	jne	3f
	addq.\s	#1,%d0
3:	printf	PCONV,"-> %p\n",1,%d0
	rts
fp_e2i_large\b:
	fp_set_sr FPSR_EXC_OPERR
	move.\s	#inf,%d0
	tst.w	(-4,%a0)
	jeq	1f
	addq.\s	#1,%d0
1:	printf	PCONV,"-> %p\n",1,%d0
	rts
fp_e2i_huge\b:
	move.\s	(%a0),%d0
	tst.l	(%a0)
	jne	1f
	tst.l	(%a0)
	jeq	fp_e2i_large\b
	| fp_normalize_ext has set this bit already
	| and made the number nonsignaling
1:	fp_tst_sr FPSR_EXC_SNAN
	jne	1f
	fp_set_sr FPSR_EXC_OPERR
1:	printf	PCONV,"-> %p\n",1,%d0
	rts
.endm

fp_conv_ext2long:
	conv_ext2int l,32

fp_conv_ext2short:
	conv_ext2int w,16

fp_conv_ext2byte:
	conv_ext2int b,8

fp_conv_ext2double:
	jsr	fp_normalize_double
	printf	PCONV,"e2d: %p(",1,%a0
	printx	PCONV,%a0@
	printf	PCONV,"), "
	move.l	(%a0)+,%d2
	cmp.w	#0x7fff,%d2
	jne	1f
	move.w	#0x7ff,%d2
	move.l	(%a0)+,%d0
	jra	2f
1:	sub.w	#0x3fff-0x3ff,%d2
	move.l	(%a0)+,%d0
	jmi	2f
	clr.w	%d2
2:	lsl.w	#5,%d2
	lsl.l	#7,%d2
	lsl.l	#8,%d2
	move.l	%d0,%d1
	lsl.l	#1,%d0
	lsr.l	#4,%d0
	lsr.l	#8,%d0
	or.l	%d2,%d0
	putuser.l %d0,(%a1)+,fp_err_ua2,%a1
	moveq	#21,%d0
	lsl.l	%d0,%d1
	move.l	(%a0),%d0
	lsr.l	#4,%d0
	lsr.l	#7,%d0
	or.l	%d1,%d0
	putuser.l %d0,(%a1),fp_err_ua2,%a1
#ifdef FPU_EMU_DEBUG
	getuser.l %a1@(-4),%d0,fp_err_ua2,%a1
	getuser.l %a1@(0),%d1,fp_err_ua2,%a1
	printf	PCONV,"%p(%08x%08x)\n",3,%a1,%d0,%d1
#endif
	rts

fp_conv_ext2single:
	jsr	fp_normalize_single
	printf	PCONV,"e2s: %p(",1,%a0
	printx	PCONV,%a0@
	printf	PCONV,"), "
	move.l	(%a0)+,%d1
	cmp.w	#0x7fff,%d1
	jne	1f
	move.w	#0xff,%d1
	move.l	(%a0)+,%d0
	jra	2f
1:	sub.w	#0x3fff-0x7f,%d1
	move.l	(%a0)+,%d0
	jmi	2f
	clr.w	%d1
2:	lsl.w	#8,%d1
	lsl.l	#7,%d1
	lsl.l	#8,%d1
	bclr	#31,%d0
	lsr.l	#8,%d0
	or.l	%d1,%d0
	printf	PCONV,"%08x\n",1,%d0
	rts

	| special return addresses for instr that
	| encode the rounding precision in the opcode
	| (e.g. fsmove,fdmove)

fp_finalrounding_single:
	addq.l	#8,%sp
	jsr	fp_normalize_ext
	jsr	fp_normalize_single
	jra	fp_finaltest

fp_finalrounding_single_fast:
	addq.l	#8,%sp 
	jsr	fp_normalize_ext
	jsr	fp_normalize_single_fast
	jra	fp_finaltest

fp_finalrounding_double:
	addq.l	#8,%sp
	jsr	fp_normalize_ext
	jsr	fp_normalize_double
	jra	fp_finaltest

	| fp_finaltest:
	| set the emulated status register based on the outcome of an
	| emulated instruction.

fp_finalrounding:
	addq.l	#8,%sp
|	printf	,"f: %p\n",1,%a0
	jsr	fp_normalize_ext
	move.w	(FPD_PREC,FPDATA),%d0
	subq.w	#1,%d0
	jcs	fp_finaltest
	jne	1f
	jsr	fp_normalize_single
	jra	2f
1:	jsr	fp_normalize_double
2:|	printf	,"f: %p\n",1,%a0
fp_finaltest:
	| First, we do some of the obvious tests for the exception
	| status byte and condition code bytes of fp_sr here, so that
	| they do not have to be handled individually by every
	| emulated instruction.
	clr.l	%d0
	addq.l	#1,%a0
	tst.b	(%a0)+			| sign
	jeq	1f
	bset	#FPSR_CC_NEG-24,%d0	| N bit
1:	cmp.w	#0x7fff,(%a0)+		| exponent
	jeq	2f
	| test for zero
	moveq	#FPSR_CC_Z-24,%d1
	tst.l	(%a0)+
	jne	9f
	tst.l	(%a0)
	jne	9f
	jra	8f
	| infinitiv and NAN
2:	moveq	#FPSR_CC_NAN-24,%d1
	move.l	(%a0)+,%d2
	lsl.l	#1,%d2			| ignore high bit
	jne	8f
	tst.l	(%a0)
	jne	8f
	moveq	#FPSR_CC_INF-24,%d1
8:	bset	%d1,%d0
9:	move.b	%d0,(FPD_FPSR+0,FPDATA)	| set condition test result
	| move instructions enter here
	| Here, we test things in the exception status byte, and set
	| other things in the accrued exception byte accordingly.
	| Emulated instructions can set various things in the former,
	| as defined in fp_emu.h.
fp_final:
	move.l	(FPD_FPSR,FPDATA),%d0
#if 0
	btst	#FPSR_EXC_SNAN,%d0	| EXC_SNAN
	jne	1f
	btst	#FPSR_EXC_OPERR,%d0	| EXC_OPERR
	jeq	2f
1:	bset	#FPSR_AEXC_IOP,%d0	| set IOP bit
2:	btst	#FPSR_EXC_OVFL,%d0	| EXC_OVFL
	jeq	1f
	bset	#FPSR_AEXC_OVFL,%d0	| set OVFL bit
1:	btst	#FPSR_EXC_UNFL,%d0	| EXC_UNFL
	jeq	1f
	btst	#FPSR_EXC_INEX2,%d0	| EXC_INEX2
	jeq	1f
	bset	#FPSR_AEXC_UNFL,%d0	| set UNFL bit
1:	btst	#FPSR_EXC_DZ,%d0	| EXC_INEX1
	jeq	1f
	bset	#FPSR_AEXC_DZ,%d0	| set DZ bit
1:	btst	#FPSR_EXC_OVFL,%d0	| EXC_OVFL
	jne	1f
	btst	#FPSR_EXC_INEX2,%d0	| EXC_INEX2
	jne	1f
	btst	#FPSR_EXC_INEX1,%d0	| EXC_INEX1
	jeq	2f
1:	bset	#FPSR_AEXC_INEX,%d0	| set INEX bit
2:	move.l	%d0,(FPD_FPSR,FPDATA)
#else
	| same as above, greatly optimized, but untested (yet)
	move.l	%d0,%d2
	lsr.l	#5,%d0
	move.l	%d0,%d1
	lsr.l	#4,%d1
	or.l	%d0,%d1
	and.b	#0x08,%d1
	move.l	%d2,%d0
	lsr.l	#6,%d0
	or.l	%d1,%d0
	move.l	%d2,%d1
	lsr.l	#4,%d1
	or.b	#0xdf,%d1
	and.b	%d1,%d0
	move.l	%d2,%d1
	lsr.l	#7,%d1
	and.b	#0x80,%d1
	or.b	%d1,%d0
	and.b	#0xf8,%d0
	or.b	%d0,%d2
	move.l	%d2,(FPD_FPSR,FPDATA)
#endif
	move.b	(FPD_FPSR+2,FPDATA),%d0
	and.b	(FPD_FPCR+2,FPDATA),%d0
	jeq	1f
	printf	,"send signal!!!\n"
1:	jra	fp_end