From 5ad647c4637e80341574ee6631ead49bf13e0299 Mon Sep 17 00:00:00 2001
From: Anton Khirnov <anton@khirnov.net>
Date: Wed, 6 Feb 2019 14:01:21 +0100
Subject: boundary: add public functions for querying boundary information

Should allow treating boundaries in a generic manner.

API bump
---
 boundary.c      | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 libmg2d.v       |  2 +-
 mg2d_boundary.h | 28 +++++++++++++++++++++++++++
 3 files changed, 88 insertions(+), 1 deletion(-)

diff --git a/boundary.c b/boundary.c
index 86803fc..419a310 100644
--- a/boundary.c
+++ b/boundary.c
@@ -16,6 +16,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include <errno.h>
 #include <stddef.h>
 #include <stdlib.h>
 
@@ -73,3 +74,61 @@ void mg2di_bc_free(MG2DBoundary **pbnd)
     free(bnd);
     *pbnd = NULL;
 }
+
+static const struct {
+    unsigned int coord_idx;
+    unsigned int is_upper;
+} boundary_def[] = {
+    [MG2D_BOUNDARY_0L] = {
+        .coord_idx = 0,
+        .is_upper  = 0,
+    },
+    [MG2D_BOUNDARY_0U] = {
+        .coord_idx = 0,
+        .is_upper  = 1,
+    },
+    [MG2D_BOUNDARY_1L] = {
+        .coord_idx = 1,
+        .is_upper  = 0
+    },
+    [MG2D_BOUNDARY_1U] = {
+        .coord_idx = 1,
+        .is_upper  = 1,
+    },
+};
+
+int mg2d_bnd_coord_idx(enum MG2DBoundaryLoc loc)
+{
+    if (loc < 0 || loc >= ARRAY_ELEMS(boundary_def))
+        return -EINVAL;
+
+    return boundary_def[loc].coord_idx;
+}
+
+int mg2d_bnd_is_upper(enum MG2DBoundaryLoc loc)
+{
+    if (loc < 0 || loc >= ARRAY_ELEMS(boundary_def))
+        return -EINVAL;
+
+    return boundary_def[loc].is_upper;
+}
+
+int mg2d_bnd_out_dir(enum MG2DBoundaryLoc loc)
+{
+    int ret = mg2d_bnd_is_upper(loc);
+
+    if (ret < 0)
+        return 0;
+
+    return ret ? 1 : -1;
+}
+
+enum MG2DBoundaryLoc mg2d_bnd_id(int coord_idx, int is_upper)
+{
+    for (int i = 0; i < ARRAY_ELEMS(boundary_def); i++) {
+        if (boundary_def[i].coord_idx == coord_idx &&
+            boundary_def[i].is_upper  == is_upper)
+            return i;
+    }
+    return MG2D_BOUNDARY_NONE;
+}
diff --git a/libmg2d.v b/libmg2d.v
index 400c46f..7fb72b7 100644
--- a/libmg2d.v
+++ b/libmg2d.v
@@ -1,4 +1,4 @@
-LIBMG2D_7 {
+LIBMG2D_8 {
     global: mg2d_*;
     local: *;
 };
diff --git a/mg2d_boundary.h b/mg2d_boundary.h
index 4a7dcee..12c897f 100644
--- a/mg2d_boundary.h
+++ b/mg2d_boundary.h
@@ -44,6 +44,10 @@ enum MG2DBCType {
  * Location of the boundary.
  */
 enum MG2DBoundaryLoc {
+    /**
+     * Undefined boundary location.
+     */
+    MG2D_BOUNDARY_NONE = -1,
     /**
      * coord0 lower
      */
@@ -94,4 +98,28 @@ typedef struct MG2DBoundary {
     MG2DBoundaryInternal *priv;
 } MG2DBoundary;
 
+/**
+ * @return index of the coordinate that is kept constant along this boundary
+ * (x: 0, y: 1)
+ */
+int mg2d_bnd_coord_idx(enum MG2DBoundaryLoc loc);
+
+/**
+ * @return 1 if this is the upper boundary, 0 for the lower one
+ */
+int mg2d_bnd_is_upper(enum MG2DBoundaryLoc loc);
+
+/**
+ * @return 1 if the corresponding variable increases in the direction from the
+ * computational domain across the boundary, -1 if it decreases.
+ *
+ * @note this is equivalent to (mg2d_bnd_is_upper(loc) ? 1 : -1)
+ */
+int mg2d_bnd_out_dir(enum MG2DBoundaryLoc loc);
+
+/**
+ * Construct the boundary id from coordinate and upper/lower specification.
+ */
+enum MG2DBoundaryLoc mg2d_bnd_id(int coord_idx, int is_upper);
+
 #endif // MG2D_BOUNDARY_H
-- 
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