add what-is-to-be-achieved preamble to visual steps bug #672

diff --git a/openpower/sv/cookbook/pospopcnt.mdwn b/openpower/sv/cookbook/pospopcnt.mdwn
index 2d04961d33bfa0dbb1e8721f911f0bcf02fc38f8..0bd79e47887fe725b90425d94bd7cbf4025050e4 100644 (file)
--- a/openpower/sv/cookbook/pospopcnt.mdwn
+++ b/openpower/sv/cookbook/pospopcnt.mdwn
@@ -77,6 +77,11 @@ bit-position, of an array of input values. Refer to Fig.2
 # Visual representation of the pospopcount algorithm
 In order to perform positional popcount we need to go 
 through series of steps shown below in figures 3, 4, 5 & 6.
+The limitation to overcome is that the CPU can only work
+on registers (horizontally) but the requirement of pospopcount
+is to add *vertically*.  Part of the challenge is therefore
+to perform an appropriate transpose of the data, in blocks
+that suit the processor and the ISA capacity.
  
 
 <img src="/openpower/sv/cookbook/BlockDivision.drawio.svg"