From 1bbca16e3fa0f2cf8e001ae6b7ff359628b06178 Mon Sep 17 00:00:00 2001
From: shahramn <shahram.najm@ecmwf.int>
Date: Tue, 12 Mar 2024 11:59:49 +0000
Subject: [PATCH] ECC-1784: Add support for N=1 nested

---
 src/grib_iterator_class_healpix.cc | 12 ++++++------
 tests/grib_grid_healpix.sh         | 26 ++++++++++++--------------
 2 files changed, 18 insertions(+), 20 deletions(-)

diff --git a/src/grib_iterator_class_healpix.cc b/src/grib_iterator_class_healpix.cc
index 0b5c09da0..7befaf894 100644
--- a/src/grib_iterator_class_healpix.cc
+++ b/src/grib_iterator_class_healpix.cc
@@ -265,8 +265,8 @@ static int iterate_healpix(grib_iterator_healpix* self, long N)
                 p -= 8 * Nside;
             }
 
-            int i = (r + p) >> 1;
-            int j = (r - p) >> 1;
+            int i = std::max(0, (r + p)) >> 1;
+            int j = std::max(0, (r - p)) >> 1;
 
             Assert(f < 12 && i < Nside && j < Nside);
             return CodecFijNest::fij_to_nest(f, i, j, k);
@@ -362,10 +362,10 @@ static int init(grib_iterator* iter, grib_handle* h, grib_arguments* args)
         grib_context_log(h->context, GRIB_LOG_ERROR, "%s: Only orderingConvention=(ring|nested) are supported", ITER);
         return GRIB_GEOCALCULUS_PROBLEM;
     }
-    if (self->nested && N == 1) {
-        grib_context_log(h->context, GRIB_LOG_ERROR, "%s: For orderingConvention=nested, N must be greater than 1", ITER);
-        return GRIB_GEOCALCULUS_PROBLEM;
-    }
+    // if (self->nested && N == 1) {
+    //     grib_context_log(h->context, GRIB_LOG_ERROR, "%s: For orderingConvention=nested, N must be greater than 1", ITER);
+    //     return GRIB_GEOCALCULUS_PROBLEM;
+    // }
 
     if (grib_is_earth_oblate(h)) {
         grib_context_log(h->context, GRIB_LOG_ERROR, "%s: Only spherical earth is supported", ITER);
diff --git a/tests/grib_grid_healpix.sh b/tests/grib_grid_healpix.sh
index 1557a84a7..7ff56382c 100755
--- a/tests/grib_grid_healpix.sh
+++ b/tests/grib_grid_healpix.sh
@@ -19,7 +19,8 @@ input=$ECCODES_SAMPLES_PATH/GRIB2.tmpl
 
 latest=`${tools_dir}/grib_get -p tablesVersionLatest $input`
 
-# Create a filter
+# Check basic keys and grid template
+# -----------------------------------
 cat > $tempFilt <<EOF
   set tablesVersion = $latest;
   set gridType = "healpix";
@@ -45,8 +46,8 @@ ${tools_dir}/grib_dump -O -p section_3 $tempGrib
 ${tools_dir}/grib_ls -jn geography $tempGrib > $tempLog
 grep -q "orderingConvention.*ring" $tempLog
 
-# Geoiterator
-# -------------
+# Geoiterator ring-ordering
+# --------------------------
 rm -f $tempGrib
 cat > $tempFilt <<EOF
   set tablesVersion = $latest;
@@ -73,8 +74,8 @@ EOF
 ${tools_dir}/grib_filter $tempFilt $tempGrib
 
 
-# Nested ordering
-# ---------------
+# Geoiterator Nested ordering
+# ---------------------------
 rm -f $tempGrib
 cat > $tempFilt <<EOF
   set tablesVersion = $latest;
@@ -105,16 +106,13 @@ set -e
 grep -q "Nside must be a power of 2" $tempLog
 
 
-# Nested. Bad N
-${tools_dir}/grib_set -s gridType=healpix,Nside=1,orderingConvention=nested $input $tempGrib
-set +e
-${tools_dir}/grib_get_data $tempGrib > $tempLog 2>&1
-status=$?
-set -e
-[ $status -ne 0 ]
-cat $tempLog
-grep -q "N must be greater than 1" $tempLog
+# Nested N=1
+input=$ECCODES_SAMPLES_PATH/GRIB2.tmpl
+${tools_dir}/grib_set -s gridType=healpix,Nside=1,orderingConvention=nested,numberOfDataPoints=12,numberOfValues=12 $input $tempGrib
+${tools_dir}/grib_get_data $tempGrib > $tempLog
 
+# Invalid cases
+# ------------------
 # Bad ordering
 ${tools_dir}/grib_set -s gridType=healpix,Nside=1,ordering=6 $input $tempGrib
 set +e