From e5e980c53990f47440ba4e2e1e2e9dc07548a662 Mon Sep 17 00:00:00 2001
From: Martin Reinecke <martin@mpa-garching.mpg.de>
Date: Wed, 17 Oct 2012 11:47:12 +0200
Subject: [PATCH] make ring sorting more determninistic

---
 libsharp/sharp.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/libsharp/sharp.c b/libsharp/sharp.c
index 6e832c3..c089ecb 100644
--- a/libsharp/sharp.c
+++ b/libsharp/sharp.c
@@ -116,7 +116,9 @@ static int ringpair_compare (const void *xa, const void *xb)
   {
   const sharp_ringpair *a=xa, *b=xb;
   if (a->r1.nph==b->r1.nph)
-    return (a->r1.phi0 < b->r1.phi0) ? -1 : (a->r1.phi0 > b->r1.phi0) ? 1 : 0;
+    return (a->r1.phi0 < b->r1.phi0) ? -1 :
+      ((a->r1.phi0 > b->r1.phi0) ? 1 :
+        (a->r1.cth>b->r1.cth ? -1 : 1));
   return (a->r1.nph<b->r1.nph) ? -1 : 1;
   }
 
@@ -186,7 +188,13 @@ void sharp_make_geom_info (int nrings, const int *nph, const ptrdiff_t *ofs,
     info->pair[info->npairs].r1=infos[pos];
     if ((pos<nrings-1) && FAPPROX(infos[pos].cth,-infos[pos+1].cth,1e-12))
       {
-      info->pair[info->npairs].r2=infos[pos+1];
+      if (infos[pos].cth>0)  // make sure northern ring is in r1
+        info->pair[info->npairs].r2=infos[pos+1];
+      else
+        {
+        info->pair[info->npairs].r1=infos[pos+1];
+        info->pair[info->npairs].r2=infos[pos];
+        }
       ++pos;
       }
     else