diff --git a/th01/math/subpixel.hpp b/th01/math/subpixel.hpp
index c0363cbd..468a3987 100644
--- a/th01/math/subpixel.hpp
+++ b/th01/math/subpixel.hpp
@@ -7,18 +7,21 @@
 
 typedef int subpixel_t;
 
+static const subpixel_t SUBPIXEL_FACTOR = 16;
+static const char SUBPIXEL_BITS = 4;
+
 #define TO_SP(v) \
-	(v << 4)
+	(v << SUBPIXEL_BITS)
 
 #define TO_PIXEL(v) \
-	(v >> 4)
+	(v >> SUBPIXEL_BITS)
 
 // In-place conversion to a pixel. Ugly, and should not exist.
 #define TO_PIXEL_INPLACE(v) \
-	(v >>= 4)
+	(v >>= SUBPIXEL_BITS)
 
 inline subpixel_t to_sp(float pixel_v) {
-	return static_cast<subpixel_t>(pixel_v * 16.0f);
+	return static_cast<subpixel_t>(pixel_v * SUBPIXEL_FACTOR);
 }
 
 inline unsigned char to_sp8(float pixel_v) {
diff --git a/th01/math/subpixel.inc b/th01/math/subpixel.inc
index c51c152f..e11a5ca1 100644
--- a/th01/math/subpixel.inc
+++ b/th01/math/subpixel.inc
@@ -1,2 +1,5 @@
 PIXEL_NONE = -999
 SUBPIXEL_NONE = (PIXEL_NONE shl 4)
+
+SUBPIXEL_FACTOR = 16
+SUBPIXEL_BITS = 4