Fix some math overflows in rgb2hsv_approximate

1 files changed, 15 insertions, 5 deletions

diff --git a/hsv2rgb.cpp b/hsv2rgb.cpp
index 9806565d..f16472fc 100644
--- a/hsv2rgb.cpp
+++ b/hsv2rgb.cpp
@@ -538,7 +538,17 @@ CHSV rgb2hsv_approximate( const CRGB& rgb)
 
     // saturation is opposite of desaturation
     s = 255 - desat;
-    if( v != 255) s = (s * 256) / v;
+    if( v != 255) {
+        // this part could probably use refinement/rethinking,
+        // (but it doesn't overflow & wrap anymore)
+        uint16_t s16;
+        s16 = (s * 256) / v;
+        if( s16 < 256) {
+            s = s16;
+        } else {
+            s = 255; // clamp to prevent overflow
+        }
+    }
 
     // undo 'dimming' of saturation
     if( s != 255 ) s = 255 - sqrt16( (255-s) * 256);
@@ -557,7 +567,7 @@ CHSV rgb2hsv_approximate( const CRGB& rgb)
         if( g == 0 ) {
             // if green is zero, we're in Purple/Pink-Red
             h = (HUE_PURPLE + HUE_PINK) / 2;
-            h += scale8( r - 128, FIXFRAC8(48,128));
+            h += scale8( qsub8(r, 128), FIXFRAC8(48,128));
         } else if ( (r - g) > g) {
             // if R-G > G then we're in Red-Orange
             h = HUE_RED;
@@ -582,7 +592,7 @@ CHSV rgb2hsv_approximate( const CRGB& rgb)
                 h += scale8( b, FIXFRAC8(32,85));
             } else {
                 h = HUE_AQUA;
-                h += scale8( b - 85, FIXFRAC8(8,42));
+                h += scale8( qsub8(b, 85), FIXFRAC8(8,42));
             }
         }
 
@@ -592,7 +602,7 @@ CHSV rgb2hsv_approximate( const CRGB& rgb)
         if( r == 0) {
             // if red is zero, we're in Aqua/Blue-Blue
             h = HUE_AQUA + ((HUE_BLUE - HUE_AQUA) / 4);
-            h += scale8( b - 128, FIXFRAC8(24,128));
+            h += scale8( qsub8(b, 128), FIXFRAC8(24,128));
         } else if ( (b-r) > r) {
             // B-R > R, we're in Blue-Purple
             h = HUE_BLUE;
@@ -600,7 +610,7 @@ CHSV rgb2hsv_approximate( const CRGB& rgb)
         } else {
             // B-R < R, we're in Purple-Pink
             h = HUE_PURPLE;
-            h += scale8( r - 85, FIXFRAC8(32,85));
+            h += scale8( qsub8(r, 85), FIXFRAC8(32,85));
         }
     }