C----------------------------------------------------------------------
        subroutine ftswi8(buffer,npix)
C
C       swap 8 successive bytes in values to convert to/from IEEE.
C               if the original byte order is: 1 2 3 4 5 6 7 8
C               the output order is:           8 7 6 5 4 3 2 1
C
C       buffer  i  input buffer of bytes to be swapped
C       npix    i  number of 8 bytes-words to be swapped
C
C       written by Wm Pence, HEASARC/GSFC, Dec 1996

C  The equivalence statements in this algorithm cause errors with
C  the Linux NAG F90 compiler.
C        integer npix, i
C        double precision buffer(npix),temp1,temp2
C        logical*1 l1(8), l2(8)
C        equivalence (temp1,l1)
C        equivalence (temp2,l2)
C
C        do 10 i=1,npix
C            temp1=buffer(i)
C            l2(8)=l1(1)
C            l2(7)=l1(2)
C            l2(6)=l1(3)
C            l2(5)=l1(4)
C            l2(4)=l1(5)
C            l2(3)=l1(6)
C            l2(2)=l1(7)
C            l2(1)=l1(8)
C            buffer(i)=temp2
C10      continue

C       alternate swapping algorithm, Wm Pence, April 97
        integer npix,i8
        logical*1 buffer(npix*8),temp

        do 10 i8=8,npix*8,8

C          swap 1st and 8th bytes
           temp=buffer(i8-7)
           buffer(i8-7)=buffer(i8)
           buffer(i8)=temp
 
C          swap 2nd and 7th bytes
           temp=buffer(i8-6)
           buffer(i8-6)=buffer(i8-1)
           buffer(i8-1)=temp

C          swap 3rd and 6th bytes
           temp=buffer(i8-5)
           buffer(i8-5)=buffer(i8-2)
           buffer(i8-2)=temp

C          swap 4th and 5th bytes
           temp=buffer(i8-4)
           buffer(i8-4)=buffer(i8-3)
           buffer(i8-3)=temp
10      continue
        end