Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1 3078~9
APPARAT~IS FQR~XTENDING WIN~QW~ l~INQZ B~F~R M~MORY
This invention r~lates to logic circuitry and, more particularly, to logic
5 circuitry which rnay be utiliz~d to increase the number of windows which may be
displaysd by a comput~r system.
is~of th~ Prior Ar~
One common interface used for oomputer operation utilizes multiple
10 ~windows" display~d on a cathode-ray tube to repres~nt individual computer
applications. In a system using windows, mor0 than one program at a tirne is
plac~d in a portion of memory available for instant call. Th~ texl and graphics
output o~ ~ach sueh program is made to app~ar in a window, a paRicular s~t o~
defined bourldari~s on the screen. Usually, the computer opera~or is operating a15 sin~le one of ~hese programs but may switch (often by a single k~ystroke~ to
anothar program in anoth~r window ~o work with that program, ~o call data Srom
that pro~ram, to plac0 data in that program, or for any numb~r of other r~asons.Each window may overlap other windows with th~ "~ront window" constituting th0
current aotive work llil~. Th~ user may add or delete information from th~ current
20 window, add n~w itams to th~ window, refile th~ window in anoth~r location, and,
~anerally, per~orm any other operations on the program in the winclow as he
mi~ht were ther~ no o1h~r window~.
Windowin~ systems hav~ b~en found to b~ quita use~ or advanced
¢omputer operation~. For exampl~, a ~killed computer operator flnds ~ndowing
:25 syst~ms to be quite useful for providing rapid shifting betwaen different programs
and docunn~nts. In a sys~m which do~s not use windowing, ~hs op~rator usually
has to close: on~ pro~ram before h~ may call up a n~w prograrn in order to work
with the n~w program. Thi~ tak~s a substan~ial amount of time. Moroov~r, a
primary reason for switchin~ b~tw33n programs is t9 transfer data and ~raphic
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images between programs. A syst~m which does no~ utilize windowing does not
usually allow the ~asy transfer of information be~wesn programs.
It was, among other things, to make the op~ration of comput~rs more rapid
and to facilitate th~ transfer of data between documen~s and pragrams that
5 windowin0 system were devised.
For complica~d tasks, it is oRen desirable to have running at the same
time any numb~r of windows, ~ach with its diff~rent individual program or
document, just as ons might have many individual documents on on~'s dssk for
use in complcting a parlicular task. However, most windowing systems are
10 incapable of providing more than a limited number of windows which may be
acc~ss~d at ona time. For example, a system disclosed in cop~nding patent
application Serial Number 599,864 , ~ntitled ~Apparatus tor Rapidly
Clearing 1he C)~nput Display of a Computer Syst~m", William Joy, et al., filed
May 16,1989 and assi~nad to th~ Assign~e of the present inv3ntion has circuitry
15 which allows a total of sixteen windows to be u~ilized at a time. Cons~quently,
such syslems still r~quire, although to a lesser d~gr~e, that th~ oparator switch
betwaen pro~rams by closing ona program befor~ opening anoth~r wherc more
~han six~a~n programs or documents ar~ involved.
I~ is, ther~fore, an object of ~he present invention to provide a comput~r
20 syst~m which includes logic circuitry defining a windowing system whioh allows
th~ seiec~ion of an essentially unlimited numbar of windows.
It is anoth~r object of this inv~ntion to provide a comput~r systam capable
of handlin~ ~ lar~e number of programs or docum~nts at on~ tima.
An additional obj~c~ of tha pr~scnt inv~ntion is ~o provide lo~ic circuitry for
ZS a computer systam which may be sclectiv~ly utilized for increasin~ the number of
windows available at ona tim~.
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=~!Q~
Thase and o~her objects of the invention ars accomplishad in a compu~er
system which includes a display memory for storin~ information to be presented
on an output display, a window identification mernory for storing infornation ~'
5 regardin~ window position on an output display, a window identifieation register
~or storing window identification numbers indica~ive of the window in which a
particular piace of data is ~o appear, a window id~ntification comparator for
determining if a number in the window iden~ification register is equal to a window
identification mJmber at a particular pixel in the window identification register, a Z
10 buffer memory for storing information indicative of tha depth of inform~tion to
appear on an output display, a Z buffer r~gister for storing inforrnation indicative
of the depth of each piece of information, a Z buffer comparator for determiningwhather the informativ~ in the Z buffer register is at a de,~h equal to or less than
the depth of the information storéd in the Z buffer memory, a window extension
15 re~is~er for storing a window numb~r great0r than is capable of storage in the
window identification ragister, a control r~gister for causin~ the storags of
window identification numbers in ths Z buff0r memory, a window extension
comparator for companng numbers storad in ~he window extsnsion register with
numb0rs stored in ~he Z buffer m0mory, and write enabie circuitry responsive to
20 the window identifioation comparator, the Z buffer comparator, and the windowextansion eompar~tor ~or causing inform~tion to be written to the window
; ~ identification mamory, ~he Z buff~r memory, and the display memory.
Thase and other ~eatures and advantages of ~ha present inYention will
become apparQnt to thos~ skillGd in the arl up~n reading ths Sollowin~ detailed
ZS d3scnption in conjunction with the several 7iglJras of ths drawin~.
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In the l)rawln~
Fi~ure 1 is a block diagram illustrative of an arrangement for provid~ a
plurality of windows disclos~d in a copendin~ patant application.
Fl~ure 2 is a block diagram illustrating an arrangament in accordance
5 with ~hs invention for increasing the number of windows available for display at
the output of a computer system.
Fi~ure 3 is a pictorial illustration of the areas mapped out by storage of
window numbers in ~ha window identification memory where a window e)dension
system is utilized in accordance with the present inv~ntion.
Fl~ure 4 is a pictorial illustration of th~ areas mapped out by storage of
window numbcrs in ths Z buffer memory where a window ~xtension system is
utilkad in accordanca with the prasant invention.
Figure 5 is a truth table which may b0 utilized in understanding the
operation of the circuitry of Figur~ 2.
1 S Fi~ure S is a diagram illustrating tha bit siz~ of ths windows and depthindications which may ba stored together in the Z buffer mcmory in one sp~cific
embodiment of ~he InvenSion.
.
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Referrin~ now to Fi~ure 1 thare is shown a windowing system for use in a
computar syst~m such as that illustrat~d in the copending patent application
refer~ed to above assigned ~o the assignee of the pr~sen~ patent application.
Fl~ure 1 illustrates a window identific~tion output syst~m 10 which is utilized to
provido output signals to a c~hode ray tube (CRT) 12 which displays the
differ~nt windows.
To produce an output on a computer output display, ~h~ screen full of
images or tex~ is r~pr~s~nt~d in a block of memory known as a "bitmap~. In its
sirnplest form, each picture el~mant ~pixel~ on the screen must be r~presented by
a memory bit. For example, if the display scre~n has 1024 by 1 û24 pix~ls, then
slightly more than on0 million bits of memory are n~c~ssary to rspresent ~ach
scre~n. In order to produce a color output, it is usual to have a number of bits of
l 5 m~mory for cach pixel of the display memory. In a preferred embodim~nt, ~ach
display memory may include twenty-four bits o~ storage for storin~ ~olor
information at ~ach pixsl. This is r~ferred to as a ~4 bit RGB color value. To store ?
these 24 bit RGB color values, the system 10 includes a pair of double-buffered
display memories 14 and 16, each of which includes a full bitmapped memory
and ar~ ~f~rrad to as m~mori~s A and ~. Th~ syst~m 10 also includes a window
identification (WID) register 18 which in a preferred embodim~nt storss four bits of
In~ormation and a window identific~tion ~NID) mernory 20 which in tho pref~ned
embodirn~nt comprises a liull s~r~en bitmapp0d m~mory which Iso stor8s ~our
~ bits of information for aach pixel.
A window id~ntification (WID) comparator 22 receives 9utput signals from
tha WID r~ister 18 and the WID mernory 20. Th~ system 10 also includ~s a
multiplexor 24, the cathsde ray tlub~ 12, writ~ enable !o~ic 26 for ~el~ctive~
enablin~ the w~itin~ of information to each o~ the display memonies A and B and
~: the window Tdentification mamory 20" and a control re~i~ter 2B for controlrlng the
3 0 op~ration o~ th0 system 10.
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In operation, windows are first sal~ct~d by values providad from a central
processin~ unit (CPU). These values include both a pixel addrcss and a window
idsntification number for each pixel to be included within ths window. The
window id~ntification numb~r is writt~n to each corresponding pix~l Iyin~ wi~hin5 the boundaries of thc particular window in th~ window identification m~mory.
Whsn a first window is written to th~ window identification memory, each memory
position within that wind~w carries th~ window identification numb~r for tha~
window. When a next windew which lies in front of the first window is writ~en to~he window identificatien memory, the portions of the second window which
10 overlay the first are wrilten on top of tha overlapped memory pesition ef the first
and, therefore, automatically cover and clip the first. After all of th~ windowsdesirad hav~ be~n stored in the window id~ntification memory, the window
identification memory has stored indications as shown in the ~isplay of the CRT
in Fi~ure 1. For example, the first window to be defined in the window
15 id~ntification memery is shown as window 0 on the CRT, the second window
(whlch overlays the first) as window 1, and the third window (which is in the
foreground) as window 2.
Wh~n it is desired te write information to ths display memory for particular
windows, thc information is wrinen inlo thc selact~d display memory A or B from
20 the CPU through ths data bus. The information includes a pixel addr~ss, an RGB
celor value as discvss~d above, and a window identification number. The
window identiflcation numb~r is stored in the window identification re~ister 18
and compared to the window id~ntification numbar previously storad for th~t pixel
in the window iden~ification memory 20. If th~ windew id~n~ification numbar
2S ~tored in the window id~ntification memory 20 is ghe sam~ as that in the window
~: idcntification r~ister 18, the compara1or circuit 22 causes the wri~e enable logic
26 to allow the FtGB in~ormation to be writ~cn to the addr~ssed pixal of the
8alsct~d display m~mory A or B. If 1he c~mparator Ci~Uitly 22 d~t~rmines that
the wîndow Id~ntifica1îon number is not th~ sam~ as th~ number stored fsr that
30 pîxeî in the window id~n~ification m~mory 20, then the RGB in~rrnatîon is nst
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1 307849
~tored in th3 display memory. Cons~quently, only at thos0 addr~ss~s of the
sel~cted display memory which are within each particular window to which the
information is addressed will signals for tha~ window be written. The si~nal written
to th~ display memory is ultimat~ly transferred frorn ths parRcular display memory
5 via a mul~iplexor controlled by the oontrol register 28 to the cathods ray tube 12
shown in Figure 1.
B0caus~ it utiiiz~s only four bits for storag~ of the window identification
number, the system 10 illustrated in Fi~ure 1 is oapable of storing information
r~lated only to sixteen windows, the total of unique binary numbers which may be10 represerlt~d in four bits. Obviously such a system cannot be utilized to prsvidP
more than sixteen windows at one time without modification. Moreover, it is avenmore obvious that the provision of a significantly larger nurnber of availabl~
window~ would render computer systams much more us~ful in many si~uations.
Th~ copending patent application referr~d to abovs also disclos~s an
l 5 arran~ement for incorporating thre~ dimensional outpu~ displays on th~ system
output devics. Th~ system incorporates apparatus for storing information
indicativ~ of the depth of each pixel to b~ provided as ou~put for a particular
display on the cathode ray tub~. Th~ particular system adds a Z buffer m~mory
whiçh stores Z or depth information valu~s and a Z buffer comparator oircuit
20 which: compares Z buffer values stored in th~ Z buffer m~mory to n~w Z valucs: for each particular pixel. Th~ Z buffer compara~or looks at the old Z value a~ ~hat
pixel position in th~ Z bu~er memory and compares it ~o the new Z valu~. If the Z
: ~ buffer comparison ~hows that ~he new Z number is less than or aqual to that
which is stor~d in m~mory, than the n~w pix~l is in a position at ~he same plane or
25~ in tront of the pixol praviously wri1tsn; and tha write enable lo~ic is activated to
: ~ writ~ th~ in~ormation r~arding that pixal to the appropriat~ dlsplay mamory snd
the Z buffer memory.
.4n arran~sment has now b~en dcvised for lnilizing the Z buffar memory
confi~uration as an ~x~ension of ~he window id~ntification m~mory to allow an
30 essentially unlimit~d numb~r of windows to be utiliz~d at one time so that
1 307849
switchin3 b0tw~en diff~rent pregrams and documents may be greatly enhanced
and the time to aceomplish th0 switching ~reatly r~duoed.
Th~ normal Z buffer memory is a full screen display memory which, iike the
~isplay memories and the window memory previously disoussed, stores at each
position r~pr~senting 2ach pixel an indic~ion of th~ par~icular position that pixel
is to tak~ alon~ the Z-a~tis. In ~he pref~rred embodim~nt of this inv~ntion, ths Z
buffer memory stores twenty-four bits for each pixel. It will be apprecia~ed that
this size of memory can stor~ individual numbers which total substantially greater
than the sixteen uniqu~ numbers which can be stcred in the window identificationmemory.` It will also be appreciated th~t any particular pro~ram or document maynot be operating in the three-dimensional domain and, eons~quently, lior that
operation the Z buffer memory circuitry v~ll be unused.
The arran~ement illustrated in Fi~ure 2 may b~ utiliz~d to 0xploit the
unused ~ buffar memory circuitry for expanding the ranye of windows which may
l 5 be used with the system. Fi~ure 2 illustrates a sys~ern 40 which includes the
display mamories 14 and 16, the WID me~nory 20, the WID re~ister 18, the WID
companson circuitry 22, the eontrol regis~er 28, and ~he write enable circuitry 26
which were used in th~ system 10 refarre~ to above in Fi~ure 1. The system 20
also includes a Z buff0r memory 42 and a Z buffer eomparision circuit 44.
In operation the circuitry of system ~0 functions as follows. Tha foli~wing
discussion presumes that both th~ windcw identifioation 20 and tha Z buff~r
func~ions have ba~n enabl~d and ~ith~r display memory A or B has becn
seleeted by ~he CPU through setting of appropriate bi~s in tho control register 28.
The system 40 operat~s to first determin~ wheth~r data are within a p~rticular
window and then to dstermine wheth~r tha data to be stored for that window lie in
froht of data already stored for that window. The first step in any operation is to
store th~ window idan~ifica~ion valu~s of ~e windows to be utiliz~d in the window
identification m~mory. This i~ acoomplish~d by writin3 to th~ window
identification m~mory 20 values from ths CPU whioh define the area of each of
the windows to b~ utiliz~d.
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When it is desir~d to write a pa~icular pixel to a display memory after the
windows to be utiliz~d have bacn dafined, the CPU provides the pix~i address
and color values alon~ with the Z (depth) valu~. In ths window idcntification
comparator circuitry 22, th~ window number of that data is compar~d wlth the
5 window identification numbQr stor0d in the window identification memory 20 andif they ar~ equal (that is, th~ information at that pixel is in that window), then an
enable signal is trans~erred to the write enable logic 26.
Presuming that the window comparison has provided an enable signal, it
is n~cessary to mak~ a Z buffer comparison in ord0r to determine whether the
10 present pixel is in front of any pixel already stored. The Z buff~r comparison
circuitry 44 compar~s th~ Z valu2 furnish~d by tll~ CPU with the Z value
previously storad in the Z buffer memory 42 for that pixel. If the Z valuQ ~urnished
by the CPU is ~qual to or less than that stored in th~ Z buffer memory 42, then the
new si~nal is in the sam~ plane or in front of the data r~pres~nting the pixel
l S pr~sently s~ored, and a signal is provided to c~use the writ~ enable lo~ic 26 to
write the Z valua to th~ Z buffer mamory 42, and the color P~t3B value to the
sel~cted display m~mory 14 or 16.
In situa~ions in which ~ha Z buffer memory 42 is not used because the
informa~ion in a particular program is not three dimensional, the Z buffer mernory
ZO 42 may ba utilized to ~xtend the number of windows which may be utilizsd in the
~ystem. This is aocomplished by th~ CPU writir~g an appropriate valu0 to the
control ~e~ister 28 which indic~t~s that a window numb~r sxtension is d~sir~d.
This causes th0 control rs~ister 28 ~o enable the Z buffer memory 42 for use as a
m0mory tor ~ ndin~ th~ numb~r o~ available w;indows. In such a cas~, the
2S unused menlory avaiiabl~ in the Z buffer memory 42 is utilizad to ~tor~ window
numbers instead. Since the pr~ferred Z buffer memory 42 includas 24 bits of
~tora~e a~ each pixal, substantially lar~er numbers of windows may be storHd.
In ord~r to allow the Z buffer m~mofy 42 ~ hJnc~ion as a window memory,
a window identi~ication extension eomparaior 46 and a window iden~ification
30 ex~ension ra~ist~r 48 ar~ add~d to ~ha systam 2û. Thas~ function in a mann~r
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I 3078~9
similar to the WID re~ist~r 18 and the WID comparator 22 to compar~ th~ window
numbar stored in tha Z buffer m~mory with the extendad window numb0r of the
incomin~ value to determine whsther the incoming Yalue is in the window to be
written. If th~ incoming and th~ storsd window number are ~qual, th~n the value
5 is written to the display m~mory. If the values do not compare, ~hen the pixel is
not in that window and is not writt~n to th~3 display memory. This arrangement
allows very large window numbers to be ~ored and a consequently large
numb~r of windows to be available without increasing thc size of the window
memory 20.
In a preferred embodim~nt of the arrangement, when~ver it is desired to
increasa the number of windows b~yond th~ normal number which may be stored
in tha window identification memory 20, the CPU writes an appropriate value intothe control registar 28 indicating that windows ar~ to be provided b~yond the
number whioh the window id~ntification m0mory 20 is capabls of handlin3.
15 Thereafter, window id~ntification valucs are represented by the contonts of the
Wl :) memory 20 and ~he Z buffer memory 42, and the WID 0xtension register 48.
Each window identification value includes ~wenty~eight bits of information and is
used for d~fining the r~gions occupied by the ~xlsnded windows in both the
window identifieation memory 20 and the Z buffar mamory 42. Each such value
20 includ~s four bits of infom~ation ~or storag~ in th~3 window id0ntifica~ion memory
20 and twenty-foL3r b-~s of information for storaga in th~ Z buff~r m~mory 42. The
portion o~ the value ~torad in the r~gion dafined for that window in ~he window
iderltifcation memory 20 d~fines thl3 r~gion as a zero numbered window whil~ thetw~nty-four bit por~ion of the ~i~nal stored in the Z buffer indicates in ~he same
25 re~ion the ~c~ual window number. In this manner, the areas wi~h a ~our bi~ ~YID
value of 0 ar~ mapp0d by the system as those desi~nat~d for th0 ext3nded
window numbers.
Thareafl~3r, wh~n it is d~sir0d to write to a window carryin~ an axtended
number, th~ inform~tion includes with Tt ~w~r,~ ht bits ~or deflnin~ the wlndow
30 numbar. In ordsr to d~t~rmin~ whsth~r the is to be writt~n ~o ~he display memory,
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the twenty-eight bit extended window identification number for the pix01 (with the
four MSB's and zeroes is sent to the WID sxtension register. The window number
in thc WID extension register 48 is compared by the WID extension comparator
46 with the number stored in the WID memory 20 and the Z buffar rnemory 42 for
5 the particular pixei. lf the WID m~mory 20 indioates that a zero is stored for that
pixel and ths Z buffar number is equal to the ramainder of tha extended window
number in the WID exiension r~gister 48, th~n the information is written to
selected display memory. In this manner the Z buffer memory 42 is utilized to
ext~nd the number of windows which may be used with the system to an
10 extremely lar~e number.
Fi~ur~ 3 illustrates the areas mapped by storage of window numbers in
the window identification mamory 20 where such a window ~xt~nsion system is
utilized. Those areas indioated with zeroes are areaà ~or which ex~end~d window
numbers are stored in the Z buffer memory 42. Fi~ure 4 illustrat~s the areas
15 mapped for th~ extended windows in the Z buffer memory 42. 1~ should be notedthat windows having window numbers 634, 653, and 712 fall in preoisely the
areas definad for z~ro windows in the window identification memory.
An sxtension of th3 system 40 utilizes a window ext~nsion mask 50. This
cirouitry receivas information from the CPU indicating the amount of th~ Z buffer
20 memoty 42 which is to be us0d for the windows exten~ion memory so that the
remainin~ portion of th~ Z buffer memory 42 may b~ us~d for d~pth information.
Th~ window ~xtension mask 50 is a register which ~n~rols ~h~ cornparator 46 by
determining which bits of the twen~y-ei~ht available should be used in ~he WID
extensiQn compara~or 46. Th~ cornplement of this mask, or th~ r~mainin~ bits of
25 the total twenty~ ht, defines lhe bits to use for the Z buffer comparatot 44. For
example, it may be d~sirabls to have some numbet of windows ~reat~r 1han
~ixtesn but less than ~he total which can b~ s~ored in hNenty-four bi~s. The
window ~xtension mask 50 may be utilized to selec:l ei~ht, twelYe, sixtaen. or
tw~nty bits, for axampl~, of the Z buffer memoly 42 for us~ as ex~0nd~d window
30 memory. IF~r example, since aight bits of memory will store window numbers
1 307849
sufficient for ~wo hundred and fifty-six windows, the window extension mask 50
may be u~ilized ~o select eight bits frorn each pixel o~ the Z buffer memory 42 for
window ext~nsion numbers leaving the remaining sixts~n bits for th~ storage of
depth information.
Ftgure 6 illustrates various options which might be utilized using the
window extension mask 50 in the systern of iFl~ure 2. In the first option, no
window number extension is used. In the second, ~ight bits are us~d for the
window number sxtension and sixte~n remain ~or the depth indication storage. In
the third ~xample, sixteen bits are used for the window number extension while
~ight bits remain for depth indications. In the last example, all of the bi~s ar~ used
to store depth in~ormation.
Fi~ure 5 is a tnJth table illustrating tho signals which may be present in
the systsm 40 shown in Fi~ure 2 and the responses of the system 40 to those
signals. The first oolumn indicates the signal provided by ~he CPU to the con~rol
register. In the first row, ~his signal is a zero indicating no window ext~nsion is
desir~d; in this cas~, if the numbers in the window id~ntification memory 20 andthe window comparator 22 are not equal, then regardless of the reelJlt of ~he
window extension comparison and the ~ buMer comparison, nothing will be
written ~o the sel~ct~d display memory and th~ Z buffer memory 42. In the n6xt
~- 20 two rows of the tabl~ where the ~ero si~nal indicates no window number
extension but 1he WID c~mparator 22 indica~es that the window indicated by the
incomin~ pix~l is aqual to tl~e window number stored at the position, the Z buffer
m~mory 42 and the display memory 20 ar~ written in accordancs ~,vith the recultsdetermined by th~ ~ buffsr comparator 44.
In the next ~hre~ rows o~ th~ tabi~ of Fl~ure 5, the control re~ister ~8
receives a si~nal indicatin~ that ths window numb~r is to ba extend~d. In sueh asiltuation, the results provid~d by ths window id~ntification comparator 22 haveno effect on ~he infonnation to be writt~n. If th~ window ex~ension compa~ison
shows unequal window numbets, th~n nothing is writtan to the Z buff~r memory
;~0 42 and ths display memory 20. If the window ex~nsion comparison shows that
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the window number of the incoming signai and that stored in th0 WID memory 20
and the Z buffer memory 42 are equal, then the result of th~ Z buffer comparisondatermin~s what is written. Jf the Z buffer comparison shows th~ Z buffer memoryto hold the window ~x!ension number of the incoming signal, th0n the information5 is written to the display memory. If the numbers are different, the information
signal is not written to the display memory.
Although the present invention has been describ~d in terms of a preferred
embodimant, it will be appreciatQd that various modifications and alterations
might be mads by those skilled in the art without departing from the spirit and
10 scop0 of th~ invention. The invention should therefora be measured in terms of
~he clairns which follow.
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