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C----------------------------------------------------------------------
subroutine ftgext(iunit,extno,xtend,status)
C 'Get Extension'
C move i/o pointer to another extension (or the primary HDU) and
C initialize all the common block parameters which describe the
C extension
C iunit i fortran unit number
C extno i number of the extension to point to.
C xtend i type of extension: 0 = the primary HDU
C 1 = an ASCII table
C 2 = a binary table
C status i output error status
C
C written by Wm Pence, HEASARC/GSFC, June, 1991
integer iunit,extno,xtend,status
C COMMON BLOCK DEFINITIONS:--------------------------------------------
integer nb,ne
parameter (nb = 20)
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
C END OF COMMON BLOCK DEFINITIONS-----------------------------------
integer ibuff,xchdu,xhdend,xmaxhd
if (status .gt. 0)return
ibuff=bufnum(iunit)
C move to the beginning of the desired extension
call ftmbyt(iunit,hdstrt(ibuff,extno),.false.,status)
if (status .le. 0)then
C temporarily save parameters
xchdu=chdu(ibuff)
xmaxhd=maxhdu(ibuff)
xhdend=hdend(ibuff)
C initialize various parameters about the CHDU
chdu(ibuff)=extno
maxhdu(ibuff)=max(extno,maxhdu(ibuff))
C the location of the END record is currently unknown, so
C temporarily just set it to a very large number
hdend(ibuff)=2000000000
C determine the structure of the CHDU
call ftrhdu(iunit,xtend,status)
if (status .gt. 0)then
C couldn't read the extension so restore previous state
chdu(ibuff)= xchdu
maxhdu(ibuff)=xmaxhd
hdend(ibuff)= xhdend
end if
end if
end
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