*** ./src/backend/utils/mmgr/aset.c.orig	2009-06-01 23:12:10.000000000 +0900
--- ./src/backend/utils/mmgr/aset.c	2009-06-02 08:47:30.000000000 +0900
***************
*** 263,268 ****
--- 263,287 ----
   *		that size <= ALLOC_CHUNK_LIMIT.
   * ----------
   */
+ #if defined(__i386__) && defined(__GNUC__)
+ /*
+  * faster version of AllocSetFreeIndex for x86 architecure.
+  * this function runs in O(1).
+  */
+ static inline int
+ AllocSetFreeIndex(Size size)
+ {
+ 	int idx;
+ 
+ 	if (__builtin_expect(size < (1 << ALLOC_MINBITS), 0))
+ 		size = (1 << ALLOC_MINBITS);
+ 
+ 	/* bsr(Bit Scan Reverse): Search the most significant set bit */
+ 	__asm__ ("bsr %1, %0" :"=r"(idx) :"g"(size - 1));
+ 
+ 	return idx - (ALLOC_MINBITS - 1);
+ }
+ #else
  static inline int
  AllocSetFreeIndex(Size size)
  {
***************
*** 281,286 ****
--- 300,306 ----
  
  	return idx;
  }
+ #endif /* defined(__i386__) && defined(__GNUC__) */
  
  #ifdef RANDOMIZE_ALLOCATED_MEMORY