[babl] tests: add a xyz to lab test

[Øyvind "pippin" Kolås <ok src gnome org>]

commit 2c9843f481579e6f9ce3a02b70c543ed4846aca6
Author: Øyvind Kolås <pippin gimp org>
Date:   Sat Oct 30 04:55:05 2021 +0200

    tests: add a xyz to lab test
    
    This is testing D50 XYZ to D50 CIE Lab the use of D50 for all XYZ and
    Lab is currently implicit in all babl code.

 tests/meson.build  |  1 +
 tests/xyz_to_lab.c | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+)
---
diff --git a/tests/meson.build b/tests/meson.build
index 5c68a78dd..eee88956e 100644
--- a/tests/meson.build
+++ b/tests/meson.build
@@ -25,6 +25,7 @@ test_names = [
   'transparent',
   'alpha_symmetric_transform',
   'types',
+  'xyz_to_lab'
 ]
 if platform_unix
   test_names += [
diff --git a/tests/xyz_to_lab.c b/tests/xyz_to_lab.c
new file mode 100644
index 000000000..dd86281c4
--- /dev/null
+++ b/tests/xyz_to_lab.c
@@ -0,0 +1,75 @@
+/* babl - dynamically extendable universal pixel conversion library.
+ * Copyright (C) 2005, Øyvind Kolås.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General
+ * Public License along with this library; if not, see
+ * <https://www.gnu.org/licenses/>.
+ */
+
+#include <math.h>
+#include <babl/babl.h>
+#include <stdio.h>
+
+#define PIXELS       4
+#define TOLERANCE    0.05
+
+float source_buf [PIXELS * 3] =
+{ 0.950, 1.000, 1.089,
+  1.000, 0.000, 0.000,
+  0.000, 1.000, 0.000,
+  0.000, 0.000, 1.000
+};
+
+float reference_buf [PIXELS * 3] =
+{ 100.00, -2.467186, -19.400648,
+  0.0, 437.147125, 0.0,
+  100.0, -431.034485, 172.4137,
+  0.0, 0.0, -185.6406,
+};
+
+float destination_buf [PIXELS * 3];
+
+static int
+test (void)
+{
+  int i;
+  int OK = 1;
+
+  babl_process (babl_fish ("CIE XYZ float", "CIE Lab float"),
+                source_buf, destination_buf,
+                PIXELS);
+
+  for (i = 0; i < PIXELS * 3; i++)
+    {
+      if (fabs (1.0 * destination_buf[i] - reference_buf[i]) > TOLERANCE)
+        {
+          fprintf (stderr, "%2i (component: %2i%%3=%i, test no: %2i/3=%i) is %f should be %f\n",
+                    i, i, i % 3, i, i / 3, destination_buf[i], reference_buf[i]);
+          OK = 0;
+        }
+    }
+  if (!OK)
+    return -1;
+  return 0;
+}
+
+int
+main (int    argc,
+      char **argv)
+{
+  babl_init ();
+  if (test ())
+    return -1;
+  babl_exit ();
+  return 0;
+}