From b462f455cbaa1d716ff6d7b83ae4e1092ba3092a Mon Sep 17 00:00:00 2001
From: Ian Jackson <ian@davenant.relativity.greenend.org.uk>
Date: Tue, 1 Jan 2008 20:30:26 +0000
Subject: [PATCH] comments etc. fixed up for new topology

---
 Makefile |  2 +-
 mgraph.h | 29 ++++++++++++-----------------
 primer.c |  4 +++-
 3 files changed, 16 insertions(+), 19 deletions(-)

diff --git a/Makefile b/Makefile
index bec227e..c40fb32 100644
--- a/Makefile
+++ b/Makefile
@@ -25,7 +25,7 @@ initial:	generator primer sgtatham/z.typescript
 		./$^ -o$@
 
 clean:
-		rm -f *.o $(TARGETS) *.new *.tmp
+		rm -f *.o $(TARGETS) *.new *.tmp *.rej *.orig
 		rm -f initial
 		rm -f *.d
 
diff --git a/mgraph.h b/mgraph.h
index de26852..22f5d92 100644
--- a/mgraph.h
+++ b/mgraph.h
@@ -33,33 +33,28 @@
  *  -3 ___ X-2 ___ X-1 ___| 0  ___  1  ___  2  ___  3  ___  4 ___
  *  0      0       0      |Y-1     Y-1     Y-1     Y-1     Y-1
  *			  |
+ *                        ^ join, where there is
+ *                           a discontinuity in numbering
+ *
  * Node x,y for
- *   0 <= x < X     x = distance along
- *   0 <= y < Y     y = distance across
+ *   0 <= x < X = 2^XBITS     x = distance along
+ *   0 <= y < Y = 2^YBITS-1     y = distance across
  *
  * Vertices are in reading order from diagram above ie x varies fastest.
  *
- * Y must be even.  The actual location opposite (0,0) is (X-(Y-1)/2,0),
- * and likewise opposite (0,Y-1) is ((Y-1)/2,0).
- *
  * Note that though presentation above is equilateral triangles, this
  * is not the case.  It's actually a square lattice with half of the
  * diagonals added.  We can't straighten it out because at the join
  * the diagonals point the other way!
  *
- * We label edges as follows:        Or in the square view:
- *
- *		    \2   /1                 2  1
- *		     \  /	            | /
- *		  ___ 0   __	            |/
- *		  3    1   0	         3--*--0
- *		     /  \	           /|
- *		   4/   5\	          / |
- *				         4  5
+ * We label edges as follows:
  *
- *                                   (This makes the numbering
- *                                   discontinuity, at the join,
- *                                   vertical and thus tractable.)
+ *		    \2   /1
+ *		     \  /
+ *		  ___ 0   __
+ *		  3    1   0
+ *		     /  \
+ *		   4/   5\
  */
 
 #ifndef MGRAPH_H
diff --git a/primer.c b/primer.c
index 3d9244a..f023b10 100644
--- a/primer.c
+++ b/primer.c
@@ -21,7 +21,9 @@ int main(int argc, const char **argv) {
     double u= y * 1.0 / (Y-1); /* SGT's u runs 0..1 across the strip */
 
     /* SGT's v runs 0..pi along the strip, where the join is at 0==pi.
-     * So that corresponds to 0..X (since 0==X in our scheme). */
+     * So that corresponds to 0..X (since 0==X in our scheme).
+     * Vertices with odd y coordinate are halfway to the next x coordinate.
+     */
     double v= (x*2 + (y&1)) * M_PI / (X*2);
 
     K printf("print %c%c( %-*.*g, %-*.*g);  # %03x %2d %2d\n",
-- 
2.30.2