Modify FastD2I to use static_cast instead of lrint(). Benchmarks show that it...

src/conversions-inl.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 23 matching lines @@
 
 // ----------------------------------------------------------------------------
 // Extra POSIX/ANSI functions for Win32/MSVC.
 
 #include "conversions.h"
 #include "platform.h"
 
 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.
 static inline unsigned int FastD2UI(double x) {
   // There is no unsigned version of lrint, so there is no fast path
   // in this function as there is in FastD2I. Using lrint doesn't work
   // for values of 2^31 and above.
 
   // Convert "small enough" doubles to uint32_t by fixing the 32
   // least significant non-fractional bits in the low 32 bits of the
@@ skipping 47 matching lines @@
   if (!isfinite(x) || x == 0) return 0;
   if (x < 0 || x >= two32) x = modulo(x, two32);
   x = (x >= 0) ? floor(x) : ceil(x) + two32;
   return (int32_t) ((x >= two31) ? x - two32 : x);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_CONVERSIONS_INL_H_