C----------------------------------------------------------------------
        subroutine ftswi4(buffer,npix)
C
C       swap 4 successive bytes in values to convert to/from IEEE.
C               if the original byte order is: 1 2 3 4
C               the output order is:           4 3 2 1
C
C       buffer  i  input buffer of bytes to be swapped
C       npix    i  number of 4 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        integer buffer(npix)
C        integer*4 temp1,temp2
C        logical*1 l1(4), l2(4)
C        equivalence (temp1,l1)
C        equivalence (temp2,l2)
C
C        do 10 i=1,npix
C            temp1=buffer(i)
C            l2(4)=l1(1)
C            l2(3)=l1(2)
C            l2(2)=l1(3)
C            l2(1)=l1(4)
C            buffer(i)=temp2
C10      continue

C       alternate swapping algorithm, Wm Pence, April 97
        integer npix,i4
        logical*1 buffer(npix*4),temp

        do 10 i4=4,npix*4,4

C          swap 1st and 4th bytes
           temp=buffer(i4-3)
           buffer(i4-3)=buffer(i4)
           buffer(i4)=temp
 
C          swap 2nd and 3rd bytes
           temp=buffer(i4-2)
           buffer(i4-2)=buffer(i4-1)
           buffer(i4-1)=temp

10      continue

        end