[gimp] Fix the linear light layer mode formula

[Alexandre Prokoudine <aprokoudine src gnome org>]

commit e69924b4eb2c1d13c03616fa5fd9bdc2eae2a4aa
Author: Alexandre Prokoudine <alexandre prokoudine gmail com>
Date:   Sun Feb 5 01:17:33 2017 +0300

    Fix the linear light layer mode formula
    
    This simpler version provides the rendering that matches
    Photoshop's one.

 .../layer-modes/gimpoperationlayermode.c           |   11 ++---------
 1 files changed, 2 insertions(+), 9 deletions(-)
---
diff --git a/app/operations/layer-modes/gimpoperationlayermode.c 
b/app/operations/layer-modes/gimpoperationlayermode.c
index 01b1297..9b11bcf 100644
--- a/app/operations/layer-modes/gimpoperationlayermode.c
+++ b/app/operations/layer-modes/gimpoperationlayermode.c
@@ -1766,7 +1766,7 @@ blendfun_vivid_light (const float *dest,
 
 
 /* added according to:
-    http://www.deepskycolors.com/archivo/2010/04/21/formulas-for-Photoshop-blending-modes.html */
+    http://www.simplefilter.de/en/basics/mixmods.html */
 static inline void
 blendfun_linear_light (const float *dest,
                        const float *src,
@@ -1782,14 +1782,7 @@ blendfun_linear_light (const float *dest,
           for (c = 0; c < 3; c++)
             {
               gfloat comp;
-              if (src[c] > 0.5f)
-                {
-                  comp = dest[c] + 2.0 * (src[c] - 0.5);
-                }
-              else
-                {
-                  comp = dest[c] + 2.0 * src[c] - 1.0;
-                }
+              comp = dest[c] + 2.0f * src[c] - 1.0f;
               out[c] = comp;
             }
         }