include "register.h"

procedure expxvw (input, dim, wndo, rcentr, rwidth,x, y, status)

#       expxvw -- Extracts locations and values of good pixels from data window
# 
#    Description:
#    ------------
#    This subroutine accepts the input vector and window mask,
#    and will, for a specified subvector size, return the locations
#    and the values of pixels within the data window. This version
#    assumes that there IS a data window mask present.
#                       ^^
#
#        Version    Date        Author     Description
#                27-JAN-1993 R. Williamson Converted to SPP
#       13     7-DEC-1983  Pat Murphy   Submitted for inspection
#           3    30-AUG-1983  PAT MURPHY   Cleverer way of scanning mask
#           2    22-AUG-1983  PAT MURPHY   add PDL and fortran
#           1    22-AUG-1983  PAT MURPHY   Prolog Generation
#
#
#

int dim	    	    	    	    	#  Size of input vector
int rwidth  	    	    	    	#  Size of output vectors
int x[rwidth]	    	    	    	#  Output positions vector
int total, i, halfsize	    	    	#  Local variables
int nn, leftmost
int status  	    	    	    	#  Returned status
real input[dim]	    	    	    	#  Input vector
real wndo[dim]   	    	    	#  Mask, assumed same size as input
real rcentr 	    	    	    	#  Location of center of range
real y[rwidth]	    	    	    	#  Output values vector

  

begin

	#  Assume all is ok
	status = OK

	#  If size of input array is exceeded
        if (rwidth > dim) {
	#  Then user is asking too much of this
	#  poor under-rated subroutine, so
	#  quit now on the unscrupulous cretin
	status = FATAL
	return
        }

	#  Store half the width of the range
        halfsize = rwidth/2
	#Init the total number of good points
        total = 0
	#  Get the location of nearest point
        nn = int (rcentr + .5)
	#  Init the loop pointer to this
        i = nn

#  Scan left of NN

        while (i >= 1 &&  total <= halfsize) {
#  If pixel is in the window mask
          if(wndo[i] == 0.0) {
#  Bump total number of valid pixels
            total = total + 1
#  and construct map of their locations
            x[total] = i
          }
#  bump pointer down till we hit one or
          i = i - 1
#  until we have enough points
        }
#  store point left of leftmost point
        leftmost = x[total] - 1
#  Start searching beyond nearest point
        i = nn + 1

#  Scan right of NN
        while (i <= dim && total < rwidth) {
#  If pixel is in the window mask
          if(wndo[i] == 0.0) {
#  Bump total number of valid pixels
            total = total + 1
#  and construct map of their locations
            x[total] = i
          }
#  bump pointer up till we hit top of
          i = i + 1
#  array or we have enough points
        }

#       One more step to do. If we have not got enough points, there may
#       be more on the left side beyond the leftmost point. If so, get them

        if (total < rwidth && leftmost > 0) {
#  Start scan at next pt
          i = leftmost
#  Scan left again
          while (i > 0 &&  total < rwidth) {
#  If pixel is in window
            if (wndo[i] == 0.0) {
#  Bump total #points
              total = total + 1
#  record point position
              x[total] = i
            }
#  bump pointer down to next pt
            i = i - 1
#  continue till we hit bottom or get
	    }

#  enough points, whichever comes first
        }

#  If this is less than the width given
        if (total != rwidth) {
#  then we can't possibly extract that
#  many points so abort now
	status = FATAL
	return
        }

#       Need to call a sorting routine here

#  Sort this array in ascending order
        call asrti (x, x, total)    	    	    	# VOPS Sort routine

#  For each location in output subvectrs
#  the y value in the sub-vector
        do i = 1, rwidth {
          y[i] = input[x[i]]
        }


end