m68k/fpsp040/round.S

21 |	round --- round result according to precision/mode
36 |	a0 is preserved and the g-r-s bits in d0 are cleared.
37 |	The result is not typed - the tag field is invalid.  The
40 |	The INEX bit of USER_FPSR will be set if the rounded result was
41 |	inexact (i.e. if any of the g-r-s bits were set).
51 |					;the appropriate g-r-s bits.
112 |	If (g=1), then add 1 to l and if (r=s=0), then clear l
117 	asll	#1,%d0			|shift g-bit to c-bit
124 |	ext_grs --- extract guard, round and sticky bits
144 	moveml	%d2/%d3,-(%a7)		|make some temp registers
148 	bfextu	LOCAL_HI(%a0){#24:#2},%d3	|sgl prec. g-r are 2 bits right
150 	lsll	%d2,%d3			|shift g-r bits to MSB of d3
151 	movel	LOCAL_HI(%a0),%d2		|get word 2 for s-bit test
152 	andil	#0x0000003f,%d2		|s bit is the or of all other
153 	bnes	st_stky			|bits to the right of g-r
160 	bfextu	LOCAL_LO(%a0){#21:#2},%d3	|dbl-prec. g-r are 2 bits right
162 	lsll	%d2,%d3			|shift g-r bits to the MSB of d3
163 	movel	LOCAL_LO(%a0),%d2		|get lower mantissa  for s-bit test
164 	andil	#0x000001ff,%d2		|s bit is the or-ing of all
165 	bnes	st_stky			|other bits to the right of g-r
168 	bras	end_sd			|if clear, exit
179 	.set	ad_1_sgl,0x00000100	|  constant to add 1 to l-bit in sgl prec
180 	.set	ad_1_dbl,0x00000800	|  constant to add 1 to l-bit in dbl prec
183 |Jump table for adding 1 to the l-bit indexed by rnd prec
196 	roxrw  LOCAL_HI(%a0)		|shift v-bit back in
197 	roxrw  LOCAL_HI+2(%a0)		|shift v-bit back in
202 	andiw  #0xfe00,LOCAL_HI+2(%a0)	|clear the l-bit
205 	clrl	LOCAL_LO(%a0)		|clear d2
212 	addql  #1,LOCAL_LO(%a0)		|add 1 to l-bit
216 	roxrw  LOCAL_HI(%a0)		|mant is 0 so restore v-bit
217 	roxrw  LOCAL_HI+2(%a0)		|mant is 0 so restore v-bit
224 	andib	#0xfe,LOCAL_LO+3(%a0)	|clear the l bit
235 	roxrw	LOCAL_HI(%a0)		|mant is 0 so restore v-bit
236 	roxrw	LOCAL_HI+2(%a0)		|mant is 0 so restore v-bit
243 	andiw	#0xf000,LOCAL_LO+2(%a0)	|clear the l-bit
276 | bit of the mantissa (msb in d1).
279 | bit of the mantissa (msb in d1) unless this would mean the exponent
280 | would go less than 0.  In that case the number becomes a denorm - the
289 |	Distance to first 1 bit in mantissa = X
301 |	L_SCR1{4} = fpte15 or ete15 bit
311 	moveml	%d2/%d3/%d5/%d6,-(%a7)
358 	movel	%d7,-(%a7)
362 	movel	%d6,-(%a7)
368 	lsll	%d7,%d0		|shift first 1 to j bit position
391 	lsll	%d7,%d1		|shift first 1 to integer bit in ms mant
394 	clrl	LOCAL_LO(%a0)	|clear ls mant
398 |	denorm --- denormalize an intermediate result
420 	btstb	#6,LOCAL_EX(%a0)	|check for exponents between $7fff-$4000
429 	clrl	%d0		|clear the sticky flag
442 	subw	LOCAL_EX(%a0),%d0	|diff = threshold - exp
446 	clrl	%d0		|else clear the sticky flag
455 	subw	LOCAL_EX(%a0),%d0	|diff = threshold - exp
459 	clrl	%d0		|else clear the sticky flag
473 	movel	#0x20000000,%d0	|set sticky bit in return value
485 |	dnrm_lp --- normalize exponent/mantissa to specified threshold
503 	movel	%d2,-(%sp)		|save d2 for temp use
506 	bfextu	WBTEMP_GRS(%a6){#6:#3},%d2	|extract guard,round, sticky  bit
515 	subw	LOCAL_EX(%a0),%d1		|d1 = threshold - uns exponent
533 	movel	%d2,-(%sp)
536 	subw	%d1,%d0			|d0 = 32 - d1
550 	andil	#0xe0000000,%d2		|clear all but G,R,S
551 	tstl	%d2			|test if original G,R,S are clear
553 	orl	#0x20000000,%d0		|set sticky bit in d0
555 	andil	#0xe0000000,%d0		|clear all but G,R,S
562 	movel	%d2,-(%sp)
566 	subw	%d1,%d0			|d0 = 32 - d1
571 	bnes	c2_sstky		|bra if sticky bit to be set
573 	bnes	c2_sstky		|bra if sticky bit to be set
585 	andil	#0xe0000000,%d2		|clear all but G,R,S
586 	tstl	%d2			|test if original G,R,S are clear
588 	orl	#0x20000000,%d0		|set sticky bit in d0
628 	lsrl	#1,%d0			|shift high bit into R bit