[gegl] negative-darkroom: speed up operation

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

commit 680b8718829dd89f610b13a3d4fd6cbe7a74d64c
Author: Richard Kreckel <kreckel ginac de>
Date:   Sun Jul 11 16:53:40 2021 +0200

    negative-darkroom: speed up operation
    
    When getting the CIEXYZ tranmittance back, use these two
    mathematical identities:
    * pow(10, a) + pow(10, b) == pow(10, a*b)
    * 1/pow(10, x) == pow(10, -x)
    
    While at it, fix the reference hash, which was broken in
    commit 3d5e9bc8be06. (This patch does not alter the hash.)

 operations/common/negative-darkroom.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)
---
diff --git a/operations/common/negative-darkroom.c b/operations/common/negative-darkroom.c
index 3677f2642..b8bbe328f 100644
--- a/operations/common/negative-darkroom.c
+++ b/operations/common/negative-darkroom.c
@@ -347,16 +347,16 @@ process (GeglOperation       *operation,
                b = (b - bMid) * o->contrast + bMid;
 
                // Simulate dye density with exponentiation to get
-               // the CIEXYZ tramsmittance back
-               out[0] = (1 / pow(10, r * curves[o->curve].cdens.X)) *
-                        (1 / pow(10, g * curves[o->curve].mdens.X)) *
-                        (1 / pow(10, b * curves[o->curve].ydens.X)) * o->illumX;
-               out[1] = (1 / pow(10, r * curves[o->curve].cdens.Y)) *
-                        (1 / pow(10, g * curves[o->curve].mdens.Y)) *
-                        (1 / pow(10, b * curves[o->curve].ydens.Y));
-               out[2] = (1 / pow(10, r * curves[o->curve].cdens.Z)) *
-                        (1 / pow(10, g * curves[o->curve].mdens.Z)) *
-                        (1 / pow(10, b * curves[o->curve].ydens.Z)) * o->illumZ;
+               // the CIEXYZ transmittance back
+               out[0] = pow(10, -(r * curves[o->curve].cdens.X +
+                                  g * curves[o->curve].mdens.X +
+                                  b * curves[o->curve].ydens.X)) * o->illumX;
+               out[1] = pow(10, -(r * curves[o->curve].cdens.Y +
+                                  g * curves[o->curve].mdens.Y +
+                                  b * curves[o->curve].ydens.Y));
+               out[2] = pow(10, -(r * curves[o->curve].cdens.Z +
+                                  g * curves[o->curve].mdens.Z +
+                                  b * curves[o->curve].ydens.Z)) * o->illumZ;
                /*printf("XYZ output %f %f %f\n", out[0], out[1], out[2]);*/
 
                in   += 3;
@@ -385,7 +385,7 @@ gegl_op_class_init (GeglOpClass *klass)
                "name",           "gegl:negative-darkroom",
                "title",          _("Negative Darkroom"),
                "categories",     "color",
-               "reference-hash", "d492ac8ef38c336aa79e63b7f39f6139",
+               "reference-hash", "2c048959d4827d580d1ab1b6635bc40b",
                "description",    _("Simulate a negative film enlargement in "
                                  "an analog darkroom."),
                NULL);