summaryrefslogtreecommitdiff
path: root/arch/m68k/fpsp040/round.S
blob: 00f98068783f32bdcaa373d04c212b54683fab2a (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
|
|	round.sa 3.4 7/29/91
|
|	handle rounding and normalization tasks
|
|
|
|		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.

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

	|section	8

#include "fpsp.h"

|
|	round --- round result according to precision/mode
|
|	a0 points to the input operand in the internal extended format
|	d1(high word) contains rounding precision:
|		ext = $0000xxxx
|		sgl = $0001xxxx
|		dbl = $0002xxxx
|	d1(low word) contains rounding mode:
|		RN  = $xxxx0000
|		RZ  = $xxxx0001
|		RM  = $xxxx0010
|		RP  = $xxxx0011
|	d0{31:29} contains the g,r,s bits (extended)
|
|	On return the value pointed to by a0 is correctly rounded,
|	a0 is preserved and the g-r-s bits in d0 are cleared.
|	The result is not typed - the tag field is invalid.  The
|	result is still in the internal extended format.
|
|	The INEX bit of USER_FPSR will be set if the rounded result was
|	inexact (i.e. if any of the g-r-s bits were set).
|

	.global	round
round:
| If g=r=s=0 then result is exact and round is done, else set
| the inex flag in status reg and continue.
|
	bsrs	ext_grs			|this subroutine looks at the
|					:rounding precision and sets
|					;the appropriate g-r-s bits.
	tstl	%d0			|if grs are zero, go force
	bne	rnd_cont		|lower bits to zero for size

	swap	%d1			|set up d1.w for round prec.
	bra	truncate

rnd_cont:
|
| Use rounding mode as an index into a jump table for these modes.
|
	orl	#inx2a_mask,USER_FPSR(%a6) |set inex2/ainex
	lea	mode_tab,%a1
	movel	(%a1,%d1.w*4),%a1
	jmp	(%a1)
|
| Jump table indexed by rounding mode in d1.w.  All following assumes
| grs != 0.
|
mode_tab:
	.long	rnd_near
	.long	rnd_zero
	.long	rnd_mnus
	.long	rnd_plus
|
|	ROUND PLUS INFINITY
|
|	If sign of fp number = 0 (positive), then add 1 to l.
|
rnd_plus:
	swap	%d1			|set up d1 for round prec.
	tstb	LOCAL_SGN(%a0)		|check for sign
	bmi	truncate		|if positive then truncate
	movel	#0xffffffff,%d0		|force g,r,s to be all f's
	lea	add_to_l,%a1
	movel	(%a1,%d1.w*4),%a1
	jmp	(%a1)
|
|	ROUND MINUS INFINITY
|
|	If sign of fp number = 1 (negative), then add 1 to l.
|
rnd_mnus:
	swap	%d1			|set up d1 for round prec.
	tstb	LOCAL_SGN(%a0)		|check for sign
	bpl	truncate		|if negative then truncate
	movel	#0xffffffff,%d0		|force g,r,s to be all f's
	lea	add_to_l,%a1
	movel	(%a1,%d1.w*4),%a1
	jmp	(%a1)
|
|	ROUND ZERO
|
|	Always truncate.
rnd_zero:
	swap	%d1			|set up d1 for round prec.
	bra	truncate
|
|
|	ROUND NEAREST
|
|	If (g=1), then add 1 to l and if (r=s=0), then clear l
|	Note that this will round to even in case of a tie.
|
rnd_near:
	swap	%d1			|set up d1 for round prec.
	asll	#1,%d0			|shift g-bit to c-bit
	bcc	truncate		|if (g=1) then
	lea	add_to_l,%a1
	movel	(%a1,%d1.w*4),%a1
	jmp	(%a1)

|
|	ext_grs --- extract guard, round and sticky bits
|
| Input:	d1 =		PREC:ROUND
| Output:	d0{31:29}=	guard, round, sticky
|
| The ext_grs extract the guard/round/sticky bits according to the
| selected rounding precision. It is called by the round subroutine
| only.  All registers except d0 are kept intact. d0 becomes an
| updated guard,round,sticky in d0{31:29}
|
| Notes: the ext_grs uses the round PREC, and therefore has to swap d1
|	 prior to usage, and needs to restore d1 to original.
|
ext_grs:
	swap	%d1			|have d1.w point to round precision
	cmpiw	#0,%d1
	bnes	sgl_or_dbl
	bras	end_ext_grs

sgl_or_dbl:
	moveml	%d2/%d3,-(%a7)		|make some temp registers
	cmpiw	#1,%d1
	bnes	grs_dbl
grs_sgl:
	bfextu	LOCAL_HI(%a0){#24:#2},%d3	|sgl prec. g-r are 2 bits right
	movel	#30,%d2			|of the sgl prec. limits
	lsll	%d2,%d3			|shift g-r bits to MSB of d3
	movel	LOCAL_HI(%a0),%d2		|get word 2 for s-bit test
	andil	#0x0000003f,%d2		|s bit is the or of all other
	bnes	st_stky			|bits to the right of g-r
	tstl	LOCAL_LO(%a0)		|test lower mantissa
	bnes	st_stky			|if any are set, set sticky
	tstl	%d0			|test original g,r,s
	bnes	st_stky			|if any are set, set sticky
	bras	end_sd			|if words 3 and 4 are clr, exit
grs_dbl:
	bfextu	LOCAL_LO(%a0){#21:#2},%d3	|dbl-prec. g-r are 2 bits right
	movel	#30,%d2			|of the dbl prec. limits
	lsll	%d2,%d3			|shift g-r bits to the MSB of d3
	movel	LOCAL_LO(%a0),%d2		|get lower mantissa  for s-bit test
	andil	#0x000001ff,%d2		|s bit is the or-ing of all
	bnes	st_stky			|other bits to the right of g-r
	tstl	%d0			|test word original g,r,s
	bnes	st_stky			|if any are set, set sticky
	bras	end_sd			|if clear, exit
st_stky:
	bset	#rnd_stky_bit,%d3
end_sd:
	movel	%d3,%d0			|return grs to d0
	moveml	(%a7)+,%d2/%d3		|restore scratch registers
end_ext_grs:
	swap	%d1			|restore d1 to original
	rts

|*******************  Local Equates
	.set	ad_1_sgl,0x00000100	|  constant to add 1 to l-bit in sgl prec
	.set	ad_1_dbl,0x00000800	|  constant to add 1 to l-bit in dbl prec


|Jump table for adding 1 to the l-bit indexed by rnd prec

add_to_l:
	.long	add_ext
	.long	add_sgl
	.long	add_dbl
	.long	add_dbl
|
|	ADD SINGLE
|
add_sgl:
	addl	#ad_1_sgl,LOCAL_HI(%a0)
	bccs	scc_clr			|no mantissa overflow
	roxrw  LOCAL_HI(%a0)		|shift v-bit back in
	roxrw  LOCAL_HI+2(%a0)		|shift v-bit back in
	addw	#0x1,LOCAL_EX(%a0)	|and incr exponent
scc_clr:
	tstl	%d0			|test for rs = 0
	bnes	sgl_done
	andiw  #0xfe00,LOCAL_HI+2(%a0)	|clear the l-bit
sgl_done:
	andil	#0xffffff00,LOCAL_HI(%a0) |truncate bits beyond sgl limit
	clrl	LOCAL_LO(%a0)		|clear d2
	rts

|
|	ADD EXTENDED
|
add_ext:
	addql  #1,LOCAL_LO(%a0)		|add 1 to l-bit
	bccs	xcc_clr			|test for carry out
	addql  #1,LOCAL_HI(%a0)		|propagate carry
	bccs	xcc_clr
	roxrw  LOCAL_HI(%a0)		|mant is 0 so restore v-bit
	roxrw  LOCAL_HI+2(%a0)		|mant is 0 so restore v-bit
	roxrw	LOCAL_LO(%a0)
	roxrw	LOCAL_LO+2(%a0)
	addw	#0x1,LOCAL_EX(%a0)	|and inc exp
xcc_clr:
	tstl	%d0			|test rs = 0
	bnes	add_ext_done
	andib	#0xfe,LOCAL_LO+3(%a0)	|clear the l bit
add_ext_done:
	rts
|
|	ADD DOUBLE
|
add_dbl:
	addl	#ad_1_dbl,LOCAL_LO(%a0)
	bccs	dcc_clr
	addql	#1,LOCAL_HI(%a0)		|propagate carry
	bccs	dcc_clr
	roxrw	LOCAL_HI(%a0)		|mant is 0 so restore v-bit
	roxrw	LOCAL_HI+2(%a0)		|mant is 0 so restore v-bit
	roxrw	LOCAL_LO(%a0)
	roxrw	LOCAL_LO+2(%a0)
	addw	#0x1,LOCAL_EX(%a0)	|incr exponent
dcc_clr:
	tstl	%d0			|test for rs = 0
	bnes	dbl_done
	andiw	#0xf000,LOCAL_LO+2(%a0)	|clear the l-bit

dbl_done:
	andil	#0xfffff800,LOCAL_LO(%a0) |truncate bits beyond dbl limit
	rts

error:
	rts
|
| Truncate all other bits
|
trunct:
	.long	end_rnd
	.long	sgl_done
	.long	dbl_done
	.long	dbl_done

truncate:
	lea	trunct,%a1
	movel	(%a1,%d1.w*4),%a1
	jmp	(%a1)

end_rnd:
	rts

|
|	NORMALIZE
|
| These routines (nrm_zero & nrm_set) normalize the unnorm.  This
| is done by shifting the mantissa left while decrementing the
| exponent.
|
| NRM_SET shifts and decrements until there is a 1 set in the integer
| bit of the mantissa (msb in d1).
|
| NRM_ZERO shifts and decrements until there is a 1 set in the integer
| bit of the mantissa (msb in d1) unless this would mean the exponent
| would go less than 0.  In that case the number becomes a denorm - the
| exponent (d0) is set to 0 and the mantissa (d1 & d2) is not
| normalized.
|
| Note that both routines have been optimized (for the worst case) and
| therefore do not have the easy to follow decrement/shift loop.
|
|	NRM_ZERO
|
|	Distance to first 1 bit in mantissa = X
|	Distance to 0 from exponent = Y
|	If X < Y
|	Then
|	  nrm_set
|	Else
|	  shift mantissa by Y
|	  set exponent = 0
|
|input:
|	FP_SCR1 = exponent, ms mantissa part, ls mantissa part
|output:
|	L_SCR1{4} = fpte15 or ete15 bit
|
	.global	nrm_zero
nrm_zero:
	movew	LOCAL_EX(%a0),%d0
	cmpw   #64,%d0          |see if exp > 64
	bmis	d0_less
	bsr	nrm_set		|exp > 64 so exp won't exceed 0
	rts
d0_less:
	moveml	%d2/%d3/%d5/%d6,-(%a7)
	movel	LOCAL_HI(%a0),%d1
	movel	LOCAL_LO(%a0),%d2

	bfffo	%d1{#0:#32},%d3	|get the distance to the first 1
|				;in ms mant
	beqs	ms_clr		|branch if no bits were set
	cmpw	%d3,%d0		|of X>Y
	bmis	greater		|then exp will go past 0 (neg) if
|				;it is just shifted
	bsr	nrm_set		|else exp won't go past 0
	moveml	(%a7)+,%d2/%d3/%d5/%d6
	rts
greater:
	movel	%d2,%d6		|save ls mant in d6
	lsll	%d0,%d2		|shift ls mant by count
	lsll	%d0,%d1		|shift ms mant by count
	movel	#32,%d5
	subl	%d0,%d5		|make op a denorm by shifting bits
	lsrl	%d5,%d6		|by the number in the exp, then
|				;set exp = 0.
	orl	%d6,%d1		|shift the ls mant bits into the ms mant
	movel	#0,%d0		|same as if decremented exp to 0
|				;while shifting
	movew	%d0,LOCAL_EX(%a0)
	movel	%d1,LOCAL_HI(%a0)
	movel	%d2,LOCAL_LO(%a0)
	moveml	(%a7)+,%d2/%d3/%d5/%d6
	rts
ms_clr:
	bfffo	%d2{#0:#32},%d3	|check if any bits set in ls mant
	beqs	all_clr		|branch if none set
	addw	#32,%d3
	cmpw	%d3,%d0		|if X>Y
	bmis	greater		|then branch
	bsr	nrm_set		|else exp won't go past 0
	moveml	(%a7)+,%d2/%d3/%d5/%d6
	rts
all_clr:
	movew	#0,LOCAL_EX(%a0)	|no mantissa bits set. Set exp = 0.
	moveml	(%a7)+,%d2/%d3/%d5/%d6
	rts
|
|	NRM_SET
|
	.global	nrm_set
nrm_set:
	movel	%d7,-(%a7)
	bfffo	LOCAL_HI(%a0){#0:#32},%d7 |find first 1 in ms mant to d7)
	beqs	lower		|branch if ms mant is all 0's

	movel	%d6,-(%a7)

	subw	%d7,LOCAL_EX(%a0)	|sub exponent by count
	movel	LOCAL_HI(%a0),%d0	|d0 has ms mant
	movel	LOCAL_LO(%a0),%d1 |d1 has ls mant

	lsll	%d7,%d0		|shift first 1 to j bit position
	movel	%d1,%d6		|copy ls mant into d6
	lsll	%d7,%d6		|shift ls mant by count
	movel	%d6,LOCAL_LO(%a0)	|store ls mant into memory
	moveql	#32,%d6
	subl	%d7,%d6		|continue shift
	lsrl	%d6,%d1		|shift off all bits but those that will
|				;be shifted into ms mant
	orl	%d1,%d0		|shift the ls mant bits into the ms mant
	movel	%d0,LOCAL_HI(%a0)	|store ms mant into memory
	moveml	(%a7)+,%d7/%d6	|restore registers
	rts

|
| We get here if ms mant was = 0, and we assume ls mant has bits
| set (otherwise this would have been tagged a zero not a denorm).
|
lower:
	movew	LOCAL_EX(%a0),%d0	|d0 has exponent
	movel	LOCAL_LO(%a0),%d1	|d1 has ls mant
	subw	#32,%d0		|account for ms mant being all zeros
	bfffo	%d1{#0:#32},%d7	|find first 1 in ls mant to d7)
	subw	%d7,%d0		|subtract shift count from exp
	lsll	%d7,%d1		|shift first 1 to integer bit in ms mant
	movew	%d0,LOCAL_EX(%a0)	|store ms mant
	movel	%d1,LOCAL_HI(%a0)	|store exp
	clrl	LOCAL_LO(%a0)	|clear ls mant
	movel	(%a7)+,%d7
	rts
|
|	denorm --- denormalize an intermediate result
|
|	Used by underflow.
|
| Input:
|	a0	 points to the operand to be denormalized
|		 (in the internal extended format)
|
|	d0:	 rounding precision
| Output:
|	a0	 points to the denormalized result
|		 (in the internal extended format)
|
|	d0	is guard,round,sticky
|
| d0 comes into this routine with the rounding precision. It
| is then loaded with the denormalized exponent threshold for the
| rounding precision.
|

	.global	denorm
denorm:
	btstb	#6,LOCAL_EX(%a0)	|check for exponents between $7fff-$4000
	beqs	no_sgn_ext
	bsetb	#7,LOCAL_EX(%a0)	|sign extend if it is so
no_sgn_ext:

	cmpib	#0,%d0		|if 0 then extended precision
	bnes	not_ext		|else branch

	clrl	%d1		|load d1 with ext threshold
	clrl	%d0		|clear the sticky flag
	bsr	dnrm_lp		|denormalize the number
	tstb	%d1		|check for inex
	beq	no_inex		|if clr, no inex
	bras	dnrm_inex	|if set, set inex

not_ext:
	cmpil	#1,%d0		|if 1 then single precision
	beqs	load_sgl	|else must be 2, double prec

load_dbl:
	movew	#dbl_thresh,%d1	|put copy of threshold in d1
	movel	%d1,%d0		|copy d1 into d0
	subw	LOCAL_EX(%a0),%d0	|diff = threshold - exp
	cmpw	#67,%d0		|if diff > 67 (mant + grs bits)
	bpls	chk_stky	|then branch (all bits would be
|				; shifted off in denorm routine)
	clrl	%d0		|else clear the sticky flag
	bsr	dnrm_lp		|denormalize the number
	tstb	%d1		|check flag
	beqs	no_inex		|if clr, no inex
	bras	dnrm_inex	|if set, set inex

load_sgl:
	movew	#sgl_thresh,%d1	|put copy of threshold in d1
	movel	%d1,%d0		|copy d1 into d0
	subw	LOCAL_EX(%a0),%d0	|diff = threshold - exp
	cmpw	#67,%d0		|if diff > 67 (mant + grs bits)
	bpls	chk_stky	|then branch (all bits would be
|				; shifted off in denorm routine)
	clrl	%d0		|else clear the sticky flag
	bsr	dnrm_lp		|denormalize the number
	tstb	%d1		|check flag
	beqs	no_inex		|if clr, no inex
	bras	dnrm_inex	|if set, set inex

chk_stky:
	tstl	LOCAL_HI(%a0)	|check for any bits set
	bnes	set_stky
	tstl	LOCAL_LO(%a0)	|check for any bits set
	bnes	set_stky
	bras	clr_mant
set_stky:
	orl	#inx2a_mask,USER_FPSR(%a6) |set inex2/ainex
	movel	#0x20000000,%d0	|set sticky bit in return value
clr_mant:
	movew	%d1,LOCAL_EX(%a0)		|load exp with threshold
	movel	#0,LOCAL_HI(%a0)	|set d1 = 0 (ms mantissa)
	movel	#0,LOCAL_LO(%a0)		|set d2 = 0 (ms mantissa)
	rts
dnrm_inex:
	orl	#inx2a_mask,USER_FPSR(%a6) |set inex2/ainex
no_inex:
	rts

|
|	dnrm_lp --- normalize exponent/mantissa to specified threshold
|
| Input:
|	a0		points to the operand to be denormalized
|	d0{31:29}	initial guard,round,sticky
|	d1{15:0}	denormalization threshold
| Output:
|	a0		points to the denormalized operand
|	d0{31:29}	final guard,round,sticky
|	d1.b		inexact flag:  all ones means inexact result
|
| The LOCAL_LO and LOCAL_GRS parts of the value are copied to FP_SCR2
| so that bfext can be used to extract the new low part of the mantissa.
| Dnrm_lp can be called with a0 pointing to ETEMP or WBTEMP and there
| is no LOCAL_GRS scratch word following it on the fsave frame.
|
	.global	dnrm_lp
dnrm_lp:
	movel	%d2,-(%sp)		|save d2 for temp use
	btstb	#E3,E_BYTE(%a6)		|test for type E3 exception
	beqs	not_E3			|not type E3 exception
	bfextu	WBTEMP_GRS(%a6){#6:#3},%d2	|extract guard,round, sticky  bit
	movel	#29,%d0
	lsll	%d0,%d2			|shift g,r,s to their positions
	movel	%d2,%d0
not_E3:
	movel	(%sp)+,%d2		|restore d2
	movel	LOCAL_LO(%a0),FP_SCR2+LOCAL_LO(%a6)
	movel	%d0,FP_SCR2+LOCAL_GRS(%a6)
	movel	%d1,%d0			|copy the denorm threshold
	subw	LOCAL_EX(%a0),%d1		|d1 = threshold - uns exponent
	bles	no_lp			|d1 <= 0
	cmpw	#32,%d1
	blts	case_1			|0 = d1 < 32
	cmpw	#64,%d1
	blts	case_2			|32 <= d1 < 64
	bra	case_3			|d1 >= 64
|
| No normalization necessary
|
no_lp:
	clrb	%d1			|set no inex2 reported
	movel	FP_SCR2+LOCAL_GRS(%a6),%d0	|restore original g,r,s
	rts
|
| case (0<d1<32)
|
case_1:
	movel	%d2,-(%sp)
	movew	%d0,LOCAL_EX(%a0)		|exponent = denorm threshold
	movel	#32,%d0
	subw	%d1,%d0			|d0 = 32 - d1
	bfextu	LOCAL_EX(%a0){%d0:#32},%d2
	bfextu	%d2{%d1:%d0},%d2		|d2 = new LOCAL_HI
	bfextu	LOCAL_HI(%a0){%d0:#32},%d1	|d1 = new LOCAL_LO
	bfextu	FP_SCR2+LOCAL_LO(%a6){%d0:#32},%d0	|d0 = new G,R,S
	movel	%d2,LOCAL_HI(%a0)		|store new LOCAL_HI
	movel	%d1,LOCAL_LO(%a0)		|store new LOCAL_LO
	clrb	%d1
	bftst	%d0{#2:#30}
	beqs	c1nstky
	bsetl	#rnd_stky_bit,%d0
	st	%d1
c1nstky:
	movel	FP_SCR2+LOCAL_GRS(%a6),%d2	|restore original g,r,s
	andil	#0xe0000000,%d2		|clear all but G,R,S
	tstl	%d2			|test if original G,R,S are clear
	beqs	grs_clear
	orl	#0x20000000,%d0		|set sticky bit in d0
grs_clear:
	andil	#0xe0000000,%d0		|clear all but G,R,S
	movel	(%sp)+,%d2
	rts
|
| case (32<=d1<64)
|
case_2:
	movel	%d2,-(%sp)
	movew	%d0,LOCAL_EX(%a0)		|unsigned exponent = threshold
	subw	#32,%d1			|d1 now between 0 and 32
	movel	#32,%d0
	subw	%d1,%d0			|d0 = 32 - d1
	bfextu	LOCAL_EX(%a0){%d0:#32},%d2
	bfextu	%d2{%d1:%d0},%d2		|d2 = new LOCAL_LO
	bfextu	LOCAL_HI(%a0){%d0:#32},%d1	|d1 = new G,R,S
	bftst	%d1{#2:#30}
	bnes	c2_sstky		|bra if sticky bit to be set
	bftst	FP_SCR2+LOCAL_LO(%a6){%d0:#32}
	bnes	c2_sstky		|bra if sticky bit to be set
	movel	%d1,%d0
	clrb	%d1
	bras	end_c2
c2_sstky:
	movel	%d1,%d0
	bsetl	#rnd_stky_bit,%d0
	st	%d1
end_c2:
	clrl	LOCAL_HI(%a0)		|store LOCAL_HI = 0
	movel	%d2,LOCAL_LO(%a0)		|store LOCAL_LO
	movel	FP_SCR2+LOCAL_GRS(%a6),%d2	|restore original g,r,s
	andil	#0xe0000000,%d2		|clear all but G,R,S
	tstl	%d2			|test if original G,R,S are clear
	beqs	clear_grs
	orl	#0x20000000,%d0		|set sticky bit in d0
clear_grs:
	andil	#0xe0000000,%d0		|get rid of all but G,R,S
	movel	(%sp)+,%d2
	rts
|
| d1 >= 64 Force the exponent to be the denorm threshold with the
| correct sign.
|
case_3:
	movew	%d0,LOCAL_EX(%a0)
	tstw	LOCAL_SGN(%a0)
	bges	c3con
c3neg:
	orl	#0x80000000,LOCAL_EX(%a0)
c3con:
	cmpw	#64,%d1
	beqs	sixty_four
	cmpw	#65,%d1
	beqs	sixty_five
|
| Shift value is out of range.  Set d1 for inex2 flag and
| return a zero with the given threshold.
|
	clrl	LOCAL_HI(%a0)
	clrl	LOCAL_LO(%a0)
	movel	#0x20000000,%d0
	st	%d1
	rts

sixty_four:
	movel	LOCAL_HI(%a0),%d0
	bfextu	%d0{#2:#30},%d1
	andil	#0xc0000000,%d0
	bras	c3com

sixty_five:
	movel	LOCAL_HI(%a0),%d0
	bfextu	%d0{#1:#31},%d1
	andil	#0x80000000,%d0
	lsrl	#1,%d0			|shift high bit into R bit

c3com:
	tstl	%d1
	bnes	c3ssticky
	tstl	LOCAL_LO(%a0)
	bnes	c3ssticky
	tstb	FP_SCR2+LOCAL_GRS(%a6)
	bnes	c3ssticky
	clrb	%d1
	bras	c3end

c3ssticky:
	bsetl	#rnd_stky_bit,%d0
	st	%d1
c3end:
	clrl	LOCAL_HI(%a0)
	clrl	LOCAL_LO(%a0)
	rts

	|end