compiler_opt.h
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 /*
  * $Id$
  * 
  * Copyright (C) 2007 iptelorg GmbH
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
  * copyright notice and this permission notice appear in all copies.
  *
  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 /*
  * compiler specific optimizations:
  * --------------------------------
  *
  *   likely(expr)         - branch predicition optimization - is more likely
  *                          that expr value will be 1 so optimize for this 
  *                          case.
  *                          Example: if (likely(p!=NULL)) {... }
  *   unlikely(expr)       - branch prediction optimization - is unlikely that 
  *                          expr will be true, so optimize for this case
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  *   prefetch(addr)        - will prefetch addr. for reading
  *   prefetch_w(addr)      - will prefetch addr. for writing
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  *   prefetch_loc_r(addr, loc) - prefetch for reading, data at addr has
  *                                no temporal locality (loc==0), a short
  *                                degree of temporal locality (loc==1), 
  *                                moderate (loc==2) or high (loc==3).
  *                                prefetch(addr) is equiv. to 
  *                                prefetch_loc_r(addr, 3).
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  *  prefetch_loc_w(addr, loc) - like above but for writing.
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  */
 /* 
  * History:
  * --------
  *  2007-05-14  created by andrei
  */
 
 #ifndef __compiler_opt_h
 #define __compiler_opt_h
 
 #if __GNUC__ >= 3
 #define likely(expr)              __builtin_expect(!!(expr), 1)
 #define unlikely(expr)            __builtin_expect(!!(expr), 0)
 
 #define prefetch(addr)            __builtin_prefetch((addr))
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 #define prefetch_w(addr)          __builtin_prefetch((addr), 1)
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 #define prefetch_loc_r(addr, loc) __builtin_prefetch((addr), 0, (loc))
 #define prefetch_loc_w(addr, loc) __builtin_prefetch((addr), 1, (loc))
 
 #else /* __GNUC__ */
 
 #warning "No compiler optimizations supported try gcc 4.x"
 #define likely(expr) (expr)
 #define unlikely(expr) (expr)
 
 #define prefetch(addr)
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 #define prefetch_w(addr)
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 #define prefetch_loc_r(addr, loc)
 #define prefetch_loc_w(addr, loc)
 #endif /* __GNUC__ */
 
 #endif