1 files changed, 12 insertions, 0 deletions
diff --git a/include/core/SkScalarCompare.h b/include/core/SkScalarCompare.h
index fee554cd2b..537d6d6dce 100644
--- a/include/core/SkScalarCompare.h
+++ b/include/core/SkScalarCompare.h
@@ -20,6 +20,18 @@
 #include "SkFloatBits.h"
 #include "SkRect.h"
 
+/** Skia can spend a lot of time just comparing scalars (e.g. quickReject).
+    When scalar==fixed, this is very fast, and when scalar==hardware-float, this
+    is also reasonable, but if scalar==software-float, then each compare can be
+    a function call and take real time. To account for that, we have the flag
+    SK_SCALAR_SLOW_COMPARES.
+ 
+    If this is defined, we have a special trick where we quickly convert floats
+    to a 2's compliment form, and then treat them as signed 32bit integers. In
+    this form we lose a few subtlties (e.g. NaNs always comparing false) but
+    we gain the speed of integer compares.
+ */
+
 #ifdef SK_SCALAR_SLOW_COMPARES
     typedef int32_t SkScalarCompareType;
     typedef SkIRect SkRectCompareType;