From b0c753681b67213741db6355930bf4a6881170df Mon Sep 17 00:00:00 2001
From: Cristy <urban-warrior@imagemagick.org>
Date: Wed, 12 Aug 2015 07:42:13 -0400
Subject: [PATCH] 
 http://www.imagemagick.org/discourse-server/viewtopic.php?f=3&t=28186

---
 MagickCore/composite.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/MagickCore/composite.c b/MagickCore/composite.c
index a68cd8e22..3fe3295c6 100644
--- a/MagickCore/composite.c
+++ b/MagickCore/composite.c
@@ -2127,15 +2127,19 @@ MagickExport MagickBooleanType CompositeImage(Image *image,
           case ModulusAddCompositeOp:
           {
             pixel=Sc+Dc;
-            if (pixel > QuantumRange)
+            while (pixel > QuantumRange)
               pixel-=QuantumRange;
+            while (pixel < 0.0)
+              pixel+=QuantumRange;
             pixel=(Sa*Da*pixel+Sa*Sc*(1.0-Da)+Da*Dc*(1.0-Sa));
             break;
           }
           case ModulusSubtractCompositeOp:
           {
             pixel=Sc-Dc;
-            if (pixel < 0.0)
+            while (pixel > QuantumRange)
+              pixel-=QuantumRange;
+            while (pixel < 0.0)
               pixel+=QuantumRange;
             pixel=(Sa*Da*pixel+Sa*Sc*(1.0-Da)+Da*Dc*(1.0-Sa));
             break;
-- 
2.40.0