Cache the results of slow math operations on machines that don't...

src/heap.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 10 matching lines @@
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #ifndef V8_HEAP_H_
 #define V8_HEAP_H_
 
+#include <math.h>
+
 #include "zone-inl.h"
 
+
 namespace v8 {
 namespace internal {
 
 // Defines all the roots in Heap.
 #define UNCONDITIONAL_STRONG_ROOT_LIST(V)                                      \
   /* Cluster the most popular ones in a few cache lines here at the top. */    \
   V(Smi, stack_limit, StackLimit)                                              \
   V(Object, undefined_value, UndefinedValue)                                   \
   V(Object, the_hole_value, TheHoleValue)                                      \
   V(Object, null_value, NullValue)                                             \
@@ skipping 1469 matching lines @@
   // On a full GC, a count of the number of marked objects.  Incremented
   // when an object is marked and decremented when an object's mark bit is
   // cleared.  Will be zero on a scavenge collection.
   int marked_count_;
 
   // The count from the end of the previous full GC.  Will be zero if there
   // was no previous full GC.
   int previous_marked_count_;
 };
 
+
+class TranscendentalCache {
+ public:
+  enum Type {ACOS, ASIN, ATAN, COS, EXP, LOG, SIN, TAN, kNumberOfCaches};
+
+  TranscendentalCache(Type t);
+
+  static inline Object* Get(Type type, double input) {

[Søren Thygesen Gjesse, 2009/09/01 08:40:31]

Please add a (short) comment on this public Get function.

+    TranscendentalCache* cache = caches_[type];

[Søren Thygesen Gjesse, 2009/09/01 08:40:31]

The description says "Cache the results of slow math operations on machines that
don't have hardware fpu instructions to execute them.", however it looks as if
the cache is always enabled. Is that intentional?

[Erik Corry, 2009/09/01 09:02:28]

The cache only works in the runtime system.  If we have an instruction for the
transcendental then we generate it inline and never normally enter the runtime
system.

+    if (cache == NULL) {
+      caches_[type] = cache = new TranscendentalCache(type);
+    }
+    return cache->Get(input);
+  }
+
+  // The cache contains raw Object pointers.  This method disposes of
+  // them before a garbage collection.
+  static void Clear();
+
+ private:
+  inline Object* Get(double input) {
+    Converter c;
+    c.dbl = input;
+    int hash = Hash(c);
+    Element e = elements_[hash];
+    if (e.in[0] == c.integers[0] &&
+        e.in[1] == c.integers[1]) {
+      ASSERT(e.output != NULL);
+      return e.output;
+    }
+    double answer = Calculate(input);
+    Object* heap_number = Heap::AllocateHeapNumber(answer);
+    if (!heap_number->IsFailure()) {
+      elements_[hash].in[0] = c.integers[0];
+      elements_[hash].in[1] = c.integers[1];
+      elements_[hash].output = heap_number;
+    }
+    return heap_number;
+  }
+
+  inline double Calculate(double input) {
+    switch(type_) {
+      case ACOS:
+        return acos(input);
+      case ASIN:
+        return asin(input);
+      case ATAN:
+        return atan(input);
+      case COS:
+        return cos(input);
+      case EXP:
+        return exp(input);
+      case LOG:
+        return log(input);
+      case SIN:
+        return sin(input);
+      case TAN:
+        return tan(input);
+      default:
+        return 0.0;  // Never happens.
+    }
+  }
+  static const int kCacheSize = 512;
+  struct Element {
+    uint32_t in[2];
+    Object* output;
+  };
+  union Converter {
+    double dbl;
+    uint32_t integers[2];
+  };
+  inline static int Hash(const Converter& c) {
+    uint32_t hash = (c.integers[0] ^ c.integers[1]);
+    hash ^= hash >> 16;
+    hash ^= hash >> 8;
+    return (hash & (kCacheSize - 1));
+  }
+  static TranscendentalCache* caches_[kNumberOfCaches];
+  Element elements_[kCacheSize];
+  Type type_;
+};
+
+
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_