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C----------------------------------------------------------------------
subroutine ftgcxi(iunit,colnum,frow,nrow,fbit,nbit,
& ivalue,status)
C read any consecutive bits from an 'X' or 'B' column as an unsigned
C n-bit integer, unless nbits=16 in which case the 16 bits
C are interpreted as a 16-bit signed 2s complement word
C iunit i fortran unit number
C colnum i number of the column to read
C frow i first row to read
C nrow i number of rows to read
C fbit i first bit within the row to read
C nbit i number of bits to read
C ivalue i*2 returned integer value(s)
C status i output error status
C
C written by Wm Pence, HEASARC/GSFC, Nov 1994
C COMMON BLOCK DEFINITIONS:--------------------------------------------
integer nf,nb,ne
parameter (nb = 20)
parameter (nf = 3000)
parameter (ne = 200)
integer bufnum,chdu,hdutyp,maxhdu,hdstrt,hdend,nxthdr,dtstrt
integer nxtfld
logical wrmode
common/ft0001/bufnum(199),chdu(nb),hdutyp(nb),maxhdu(nb),
& wrmode(nb),hdstrt(nb,ne),hdend(nb),nxthdr(nb),dtstrt(nb),nxtfld
integer tfield,tstart,tbcol,rowlen,tdtype,trept,tnull,scount
integer theap,nxheap
double precision tscale,tzero
common/ft0002/tfield(nb),tstart(nb),tbcol(nf),rowlen(nb),
& tdtype(nf),trept(nf),tscale(nf),tzero(nf),tnull(nf),scount(nb)
& ,theap(nb),nxheap(nb)
C END OF COMMON BLOCK DEFINITIONS-----------------------------------
integer iunit,colnum,fbit,nbit,frow,nrow,status,i,j,k,row,ibuff
integer*2 ivalue(*),ival,power2(16)
logical lray(16)
save power2
data power2/1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,
& 16384,0/
if (status .gt. 0)return
ibuff=bufnum(iunit)
if (nbit .gt. 16)then
call ftpmsg('Cannot read more than 16 bits (ftgcxi)')
status=308
return
else if ((fbit+nbit+6)/8 .gt. trept(colnum+tstart(ibuff)))then
call ftpmsg('Asked to read more bits than exist in'//
& ' the column (ftgcxi)')
status=308
return
end if
row=frow-1
do 30 k=1,nrow
row=row+1
C get the individual bits
call ftgcx(iunit,colnum,row,fbit,nbit,lray,status)
if (status .gt. 0)return
ival=0
j=0
if (nbit .eq. 16 .and. lray(1))then
C interprete this as a 16 bit negative integer
do 10 i=16,2,-1
j=j+1
if (.not. lray(i))ival=ival+power2(j)
10 continue
C make 2's complement
ivalue(k)=-ival-1
else
C reconstruct the positive integer value
do 20 i=nbit,1,-1
j=j+1
if (lray(i))ival=ival+power2(j)
20 continue
ivalue(k)=ival
end if
30 continue
end
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