Explicitly cast unorms to float during YUV conversion, fixing clang warning

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 44bf57f..b5d1450 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,9 @@
 ### Added
 - Enable still picture mode with rav1e >= 0.3.0 (cryptomilk)
 
+### Changed
+- Explicitly cast unorms to float during YUV conversion, fixing clang warning
+
 ## [0.5.4] - 2020-01-21
 ### Changed
 - Fix monochrome inputs on avifImageCopy. Monochrome still isn't really a first-class citizen in libavif, but this should at least honor the incoming data better.

src/reformat.c

diff --git a/src/reformat.c b/src/reformat.c
index 0278fdf..457abe2 100644
--- a/src/reformat.c
+++ b/src/reformat.c
@@ -220,9 +220,9 @@
             }
 
             // Convert unorm to float
-            const float Y = unormY / maxChannel;
-            const float Cb = (unormU / maxChannel) - 0.5f;
-            const float Cr = (unormV / maxChannel) - 0.5f;
+            const float Y = (float)unormY / maxChannel;
+            const float Cb = ((float)unormU / maxChannel) - 0.5f;
+            const float Cr = ((float)unormV / maxChannel) - 0.5f;
 
             float R = Y + (2 * (1 - kr)) * Cr;
             float B = Y + (2 * (1 - kb)) * Cb;
@@ -264,7 +264,7 @@
             }
 
             // Convert unorm to float
-            const float Y = unormY / maxChannel;
+            const float Y = (float)unormY / maxChannel;
             const float Cb = -0.5f;
             const float Cr = -0.5f;
 
@@ -318,9 +318,9 @@
             }
 
             // Convert unorm to float
-            const float Y = unormY / maxChannel;
-            const float Cb = (unormU / maxChannel) - 0.5f;
-            const float Cr = (unormV / maxChannel) - 0.5f;
+            const float Y = (float)unormY / maxChannel;
+            const float Cb = ((float)unormU / maxChannel) - 0.5f;
+            const float Cr = ((float)unormV / maxChannel) - 0.5f;
 
             float R = Y + (2 * (1 - kr)) * Cr;
             float B = Y + (2 * (1 - kb)) * Cb;
@@ -362,7 +362,7 @@
             }
 
             // Convert unorm to float
-            const float Y = unormY / maxChannel;
+            const float Y = (float)unormY / maxChannel;
             const float Cb = -0.5f;
             const float Cr = -0.5f;