argred.s

<B>Digital的Unix操作系统VAX 4.2源码</B>

signoff1:
	subl2	$4,r3
	ashq	r2,(r3),r8
	bgeq	signoff2
	incl	r10
signoff2:
	subl2	$4,r3
	ashq	r2,(r3),r7
	bgeq	signoff3
	incl	r9
signoff3:
#						p.5
#
#  Multiply the contents of  r0/r1  by the 
#  slice of  2/pi  in  r11 - r8 .
#
	emul	r0,r8,$0,r4
	emul	r0,r9,r5,r5
	emul	r0,r10,r6,r6

	emul	r1,r8,$0,r7
	emul	r1,r9,r8,r8
	emul	r1,r10,r9,r9
	emul	r1,r11,r10,r10

	addl2	r4,r8
	adwc	r5,r9
	adwc	r6,r10
#						p.6
#
#  If there are more than five leading zeros
#  after the first two quotient bits or if there
#  are more than five leading ones after the first
#  two quotient bits, generate more fraction bits.
#  Otherwise, branch to code to produce the result.
#
	bicl3	$0xc1ffffff,r10,r4
	beql	more1
	cmpl	$0x3e000000,r4
	bneq	result
more1:
#						p.7
#
#  generate another  32  result bits.
#
	subl2	$4,r3
	ashq	r2,(r3),r5
	bgeq	signoff4

	emul	r1,r6,$0,r4
	addl2	r1,r5
	emul	r0,r6,r5,r5
	addl2	r0,r6
	brb	addbits1

signoff4:
	emul	r1,r6,$0,r4
	emul	r0,r6,r5,r5

addbits1:
	addl2	r5,r7
	adwc	r6,r8
	adwc	$0,r9
	adwc	$0,r10
#						p.8
#
#  Check for massive cancellation.
#
	bicl3	$0xc0000000,r10,r6
#	bneq	more2			-S.McD  Test was backwards
	beql	more2
	cmpl	$0x3fffffff,r6
	bneq	result
more2:
#						p.9
#
#  If massive cancellation has occurred,
#  generate another  24  result bits.
#  Testing has shown there will always be 
#  enough bits after this point.
#
	subl2	$4,r3
	ashq	r2,(r3),r5
	bgeq	signoff5

	emul	r0,r6,r4,r5
	addl2	r0,r6
	brb	addbits2

signoff5:
	emul	r0,r6,r4,r5

addbits2:
	addl2	r6,r7
	adwc	$0,r8
	adwc	$0,r9
	adwc	$0,r10
#						p.10
#
#  The following code produces the reduced
#  argument from the product bits contained
#  in  r10 - r7 .
#
result:
#
#  Extract the octant number from  r10 .
#
#	extzv	$29,$3,r10,r0	...used for  pi/4  reduction -S.McD
	extzv	$30,$2,r10,r0
#
#  Clear the octant bits in  r10 .
#
#	bicl2	$0xe0000000,r10	...used for  pi/4  reduction -S.McD
	bicl2	$0xc0000000,r10
#
#  Zero the sign flag.
#
	clrl	r5
#						p.11
#
#  Check to see if the fraction is greater than
#  or equal to one-half.  If it is, add one 
#  to the octant number, set the sign flag
#  on, and replace the fraction with  1 minus
#  the fraction.
#
#	bitl	$0x10000000,r10		...used for  pi/4  reduction -S.McD
	bitl	$0x20000000,r10
	beql	small
	incl	r0
	incl	r5
#	subl3	r10,$0x1fffffff,r10	...used for  pi/4  reduction -S.McD
	subl3	r10,$0x3fffffff,r10
	mcoml	r9,r9
	mcoml	r8,r8
	mcoml	r7,r7
small:
#						p.12
#
##  Test whether the first  29  bits of the ...used for  pi/4  reduction -S.McD
#  Test whether the first  30  bits of the 
#  fraction are zero.
#
	tstl	r10
	beql	tiny
#
#  Find the position of the first one bit in  r10 .
#
	cvtld	r10,r1
	extzv	$7,$7,r1,r1
#
#  Compute the size of the shift needed.
#
	subl3	r1,$32,r6
#
#  Shift up the high order  64  bits of the
#  product.
#
	ashq	r6,r9,r10
	ashq	r6,r8,r9
	brb	mult
#						p.13
#
#  Test to see if the sign bit of  r9  is on.
#
tiny:
	tstl	r9
	bgeq	tinier
#
#  If it is, shift the product bits up  32  bits.
#
	movl	$32,r6
	movq	r8,r10
	tstl	r10
	brb	mult
#						p.14
#
#  Test whether  r9  is zero.  It is probably
#  impossible for both  r10  and  r9  to be
#  zero, but until proven to be so, the test
#  must be made.
#
tinier:
	beql	zero
#
#  Find the position of the first one bit in  r9 .
#
	cvtld	r9,r1
	extzv	$7,$7,r1,r1
#
#  Compute the size of the shift needed.
#
	subl3	r1,$32,r1
	addl3	$32,r1,r6
#
#  Shift up the high order  64  bits of the
#  product.
#
	ashq	r1,r8,r10
	ashq	r1,r7,r9
	brb	mult
#						p.15
#
#  The following code sets the reduced
#  argument to zero.
#
zero:
	clrl	r1
	clrl	r2
	clrl	r3
	brw	return
#						p.16
#
#  At this point,  r0  contains the octant number,
#  r6  indicates the number of bits the fraction
#  has been shifted,  r5  indicates the sign of
#  the fraction,  r11/r10  contain the high order
#  64  bits of the fraction, and the condition
#  codes indicate where the sign bit of  r10
#  is on.  The following code multiplies the
#  fraction by  pi/2 .
#
mult:
#
#  Save  r11/r10  in  r4/r1 .		-S.McD
	movl	r11,r4
	movl	r10,r1
#
#  If the sign bit of  r10  is on, add  1  to  r11 .
#
	bgeq	signoff6
	incl	r11
signoff6:
#						p.17
#
#  Move  pi/2  into  r3/r2 .
#
	movq	$0xc90fdaa22168c235,r2
#
#  Multiply the fraction by the portion of  pi/2
#  in  r2 .
#
	emul	r2,r10,$0,r7
	emul	r2,r11,r8,r7
#
#  Multiply the fraction by the portion of  pi/2 
#  in  r3 .
	emul	r3,r10,$0,r9
	emul	r3,r11,r10,r10
#
#  Add the product bits together.
#
	addl2	r7,r9
	adwc	r8,r10
	adwc	$0,r11
#
#  Compensate for not sign extending  r8  above.-S.McD
#
	tstl	r8
	bgeq	signoff6a
	decl	r11
signoff6a:
#
#  Compensate for  r11/r10  being unsigned.	-S.McD
#
	addl2	r2,r10
	adwc	r3,r11
#
#  Compensate for  r3/r2  being unsigned.	-S.McD
#
	addl2	r1,r10
	adwc	r4,r11
#						p.18
#
#  If the sign bit of  r11  is zero, shift the
#  product bits up one bit and increment  r6 .
#
	blss	signon
	incl	r6
	ashq	$1,r10,r10
	tstl	r9
	bgeq	signoff7
	incl	r10
signoff7:
signon:
#						p.19
#
#  Shift the  56  most significant product
#  bits into  r9/r8 .  The sign extension
#  will be handled later.
#
	ashq	$-8,r10,r8
#
#  Convert the low order  8  bits of  r10
#  into an F-format number.
#
	cvtbf	r10,r3
#
#  If the result of the conversion was
#  negative, add  1  to  r9/r8 .
#
	bgeq	chop
	incl	r8
	adwc	$0,r9
#
#  If  r9  is now zero, branch to special
#  code to handle that possibility.
#
	beql	carryout
chop:
#						p.20
#
#  Convert the number in  r9/r8  into
#  D-format number in  r2/r1 .
#
	rotl	$16,r8,r2
	rotl	$16,r9,r1
#
#  Set the exponent field to the appropriate
#  value.  Note that the extra bits created by
#  sign extension are now eliminated.
#
	subw3	r6,$131,r6
	insv	r6,$7,$9,r1
#
#  Set the exponent field of the F-format
#  number in  r3  to the appropriate value.
#
	tstf	r3
	beql	return
#	extzv	$7,$8,r3,r4	-S.McD
	extzv	$7,$7,r3,r4
	addw2	r4,r6
#	subw2	$217,r6		-S.McD
	subw2	$64,r6
	insv	r6,$7,$8,r3
	brb	return
#						p.21
#
#  The following code generates the appropriate 
#  result for the unlikely possibility that
#  rounding the number in  r9/r8  resulted in 
#  a carry out.
#
carryout:
	clrl	r1
	clrl	r2
	subw3	r6,$132,r6
	insv	r6,$7,$9,r1
	tstf	r3
	beql	return
	extzv	$7,$8,r3,r4
	addw2	r4,r6
	subw2	$218,r6
	insv	r6,$7,$8,r3
#						p.22
#
#  The following code makes an needed
#  adjustments to the signs of the 
#  results or to the octant number, and
#  then returns.
#
return:
#
#  Test if the fraction was greater than or 
#  equal to  1/2 .  If so, negate the reduced
#  argument.
#
	blbc	r5,signoff8
	mnegf	r1,r1
	mnegf	r3,r3
signoff8:
#						p.23
#
#  If the original argument was negative,
#  negate the reduce argument and
#  adjust the octant number.
#
	tstw	(sp)+
	bgeq	signoff9
	mnegf	r1,r1
	mnegf	r3,r3
#	subb3	r0,$8,r0	...used for  pi/4  reduction -S.McD
	subb3	r0,$4,r0
signoff9:
#
#  Clear all unneeded octant bits.
#
#	bicb2	$0xf8,r0	...used for  pi/4  reduction -S.McD
	bicb2	$0xfc,r0
#
#  Return.
#
	rsb