finish listing bit uses

diff --git a/layout/segcmapassign b/layout/segcmapassign
index 1fa5bdb5c6eb363fd17549090f07cb6bd2a546d2..3de3fd3e388e84d8b20c41f4ecf73adbfe26ea6a 100755 (executable)
--- a/layout/segcmapassign
+++ b/layout/segcmapassign
@@ -1,5 +1,5 @@
 #!/usr/bin/perl
-# input:
+# input file:
 #   lines, with one canonical subsegment specification (csss) each
 #   (need not be unique)
 # output:
@@ -11,16 +11,21 @@
 #         ...code to compute and stack red in range [0,1>...
 #          <green> <blue> setrgbcolor
 #
-# Encoding is as follows:
+# Encoding is as follows (bits from MSbit to LSbit):
 #
 #  RED
-#     6 bits angle
-#     1 bit `edge or core' (currently 0 meaning `core')
 #     1 bit reserved (0)
+#     1 bit `edge or core' (currently 0 meaning `core')
+#     6 bits angle
 #
 #  GREEN
 #     2 bits segment overflow
-#     6 bits moveable feature
+#     6 bits moveable feature and position
+#          each moveable feature has an unambiguous prefix
+#          the remainder of the bits are the position of that feature
+#       the feature all-bits-1 (0b1111111) is for fixed track
+#       (so every moveable feature prefix must contain at least one 0)
 #
-#  
-#  10 bits 
+#  BLUE
+#     8 bits segment main
+