From 1b6c14691b6437bec5522300a4cbb31d8037d441 Mon Sep 17 00:00:00 2001
From: Godzil <godzil@godzil.net>
Date: Wed, 4 Mar 2020 16:15:49 +0000
Subject: [PATCH] fmod is not mathematically valid. Replace it by a correct
 one.

---
 source/include/math_helper.h     | 5 +++++
 source/pattern/checkerspattern.h | 2 +-
 source/pattern/ringpattern.h     | 2 +-
 source/pattern/strippattern.h    | 2 +-
 source/uvpattern/uv_checkers.h   | 2 +-
 5 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/source/include/math_helper.h b/source/include/math_helper.h
index 7318233..cde096c 100644
--- a/source/include/math_helper.h
+++ b/source/include/math_helper.h
@@ -23,4 +23,9 @@ double max3(double a, double b, double c);
 
 double frand();
 
+static double modulo(double a, double b)
+{
+    return a - floor(a/b) * b;
+}
+
 #endif /* DORAYME_MATH_HELPER_H */
diff --git a/source/pattern/checkerspattern.h b/source/pattern/checkerspattern.h
index 1556fe3..d04f9e7 100644
--- a/source/pattern/checkerspattern.h
+++ b/source/pattern/checkerspattern.h
@@ -20,7 +20,7 @@ public:
     {
         double value = floor(point.x) + floor(point.y) + floor(point.z);
 
-        return (fmod(value, 2) == 0)?this->a:this->b;
+        return (modulo(value, 2) == 0)?this->a:this->b;
     }
 
     void dumpMe(FILE *fp) {
diff --git a/source/pattern/ringpattern.h b/source/pattern/ringpattern.h
index 79fc913..402b87c 100644
--- a/source/pattern/ringpattern.h
+++ b/source/pattern/ringpattern.h
@@ -22,7 +22,7 @@ public:
 
         double value = floor(sqrt(squared));
 
-        return (fmod(value, 2) == 0)?this->a:this->b;
+        return (modulo(value, 2) == 0)?this->a:this->b;
     }
 
     void dumpMe(FILE *fp) {
diff --git a/source/pattern/strippattern.h b/source/pattern/strippattern.h
index f7732e9..e705790 100644
--- a/source/pattern/strippattern.h
+++ b/source/pattern/strippattern.h
@@ -21,7 +21,7 @@ public:
 
     Colour patternAt(Tuple point)
     {
-        if (fmod(floor(point.x), 2) == 0)
+        if (modulo(floor(point.x), 2) == 0)
         {
             return this->a;
         }
diff --git a/source/uvpattern/uv_checkers.h b/source/uvpattern/uv_checkers.h
index c03d686..44bd96a 100644
--- a/source/uvpattern/uv_checkers.h
+++ b/source/uvpattern/uv_checkers.h
@@ -21,7 +21,7 @@ public:
         double u2 = floor(u * this->width);
         double v2 = floor(v * this->height);
 
-        if (fmod((u2 + v2), 2) == 0)
+        if (modulo((u2 + v2), 2) == 0)
         {
             return this->a;
         }