Reviewers: Mads Ager,
Description:
Modify FastD2I to use static_cast instead of lrint(). Benchmarks show that
it's
much faster this way.
Please review this at http://codereview.chromium.org/1128010
SVN Base: http://v8.googlecode.com/svn/branches/bleeding_edge/
Affected files:
M src/conversions-inl.h
M src/conversions.h
Index: src/conversions-inl.h
===================================================================
--- src/conversions-inl.h (revision 4210)
+++ src/conversions-inl.h (working copy)
@@ -41,24 +41,6 @@
namespace v8 {
namespace internal {
-// The fast double-to-int conversion routine does not guarantee
-// rounding towards zero.
-static inline int FastD2I(double x) {
-#ifdef __USE_ISOC99
- // The ISO C99 standard defines the lrint() function which rounds a
- // double to an integer according to the current rounding direction.
- return lrint(x);
-#else
- // This is incredibly slow on Intel x86. The reason is that rounding
- // towards zero is implied by the C standard. This means that the
- // status register of the FPU has to be changed with the 'fldcw'
- // instruction. This completely stalls the pipeline and takes many
- // hundreds of clock cycles.
- return static_cast<int>(x);
-#endif
-}
-
-
// The fast double-to-unsigned-int conversion routine does not guarantee
// rounding towards zero, or any reasonable value if the argument is larger
// than what fits in an unsigned 32-bit integer.
Index: src/conversions.h
===================================================================
--- src/conversions.h (revision 4210)
+++ src/conversions.h (working copy)
@@ -36,7 +36,12 @@
// rounding towards zero.
// The result is unspecified if x is infinite or NaN, or if the rounded
// integer value is outside the range of type int.
-static inline int FastD2I(double x);
+static inline int FastD2I(double x) {
+ // The static_cast convertion from double to int used to be slow, but
+ // as new benchmarks show, now it is much faster than lrint().
+ return static_cast<int>(x);
+}
+
static inline unsigned int FastD2UI(double x);
--
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