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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+# ABSU -- Vector block sum.  Each pixel in the output vector is the
+# sum of the input vector over a block of pixels.  The input vector must
+# be at least (nblocks * npix_per_block) pixels in length.
+
+procedure absud (a, b, nblocks, npix_per_block)
+
+double	a[ARB]			# input vector
+double	b[nblocks]		# output vector
+int	nblocks			# number of blocks (pixels in output vector)
+int	npix_per_block		# number of input pixels per block
+
+double	sum
+
+int	i, j
+int	block_offset, next_block, block_length
+
+begin
+	block_offset = 1
+	block_length = npix_per_block
+
+	if (block_length <= 1)
+	    call amovd (a[block_offset], b, nblocks)
+	else {
+	    do j = 1, nblocks {
+		next_block = block_offset + block_length
+		sum = 0
+		do i = block_offset, next_block - 1
+		    sum = sum + a[i]
+		b[j] = sum
+		block_offset = next_block
+	    }
+	}
+end