chiark - git - mdw - catacomb/blob - base/dispatch.h

   1 /* -*-c-*-
   2  *
   3  * CPU-specific dispatch
   4  *
   5  * (c) 2015 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of Catacomb.
  11  *
  12  * Catacomb is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU Library General Public License as
  14  * published by the Free Software Foundation; either version 2 of the
  15  * License, or (at your option) any later version.
  16  *
  17  * Catacomb is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU Library General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with Catacomb; if not, write to the Free
  24  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  25  * MA 02111-1307, USA.
  26  */
  27
  28 #ifndef CATACOMB_DISPATCH_H
  29 #define CATACOMB_DISPATCH_H
  30
  31 #ifdef __cplusplus
  32   extern "C" {
  33 #endif
  34
  35 /*----- Header files ------------------------------------------------------*/
  36
  37 #include <mLib/macros.h>
  38
  39 /*----- Macros ------------------------------------------------------------*/
  40
  41 /* --- Atomic data access machinery --- *
  42  *
  43  * If they're available, use GCC's `__atomic_*' intrinsics.  If that doesn't
  44  * work and we're using one of a small number of processors I'm sure won't
  45  * mind, then just stick with simple memory access.  Otherwise turn
  46  * dispatching off, because it probably isn't thread-safe.
  47  */
  48
  49 #if GCC_VERSION_P(4, 7)
  50 #  define CPU_DISPATCH_P 1
  51 #  define DISPATCH_LOAD(g, v)                                           \
  52         ((v) = __atomic_load_n(&(g), __ATOMIC_RELAXED))
  53 #  define DISPATCH_STORE(g, v)                                          \
  54         (__atomic_store_n(&(g), (v), __ATOMIC_RELAXED))
  55 #elif defined(__i386__) || defined(__amd64__) ||                        \
  56       defined(__arm__) || defined(__aarch64__) ||                       \
  57       defined(__mips__)
  58 #  define CPU_DISPATCH_P 1
  59 #  define DISPATCH_LOAD(g, v) ((v) = (g))
  60 #  define DISPATCH_STORE(g, v) ((g) = (v))
  61 #endif
  62
  63 /* --- A simple hack --- */
  64
  65 #ifndef EMPTY
  66 #  define EMPTY
  67 #endif
  68
  69 /* --- @CPU_DISPATCH@ --- *
  70  *
  71  * Arguments:   @stcls@ = storage class for the main @ext@ function
  72  *                      (typically either @static@ or @EMPTY@)
  73  *              @rtn@ = prefix for tail-calling a function of the appropriate
  74  *                      type (either @(void)@ or @return@)
  75  *              @ret@ = return type for the function
  76  *              @ext@ = name for the main function (other named are derived
  77  *                      from this)
  78  *              @argdecls@ = parenthesis-enclosed list of argument types
  79  *              @args@ = parenthesis-enclosed list of argument names only
  80  *              @pick@ = function to select appropriate implementation
  81  *              @dflt@ = fallback implementation
  82  *
  83  * Use:         Main machinery for CPU-specfic dispatching.
  84  *
  85  *              The macro defines a function
  86  *
  87  *                      @stcls ret ext argdcls@
  88  *
  89  *              The first time @ext@ is called, it will invoke @pick@ to
  90  *              select and a return a pointer to an appropriate
  91  *              implementation for the runtime environment.  Subsequent calls
  92  *              to @ext@ will (usually) call this preferred implementation
  93  *              directly.
  94  *
  95  *              Some target platforms may not be able to establish the
  96  *              necessary function pointer in a threadsafe way.  On such
  97  *              platforms, the dispatch machinery is disabled and @ext@ will
  98  *              simply call @dflt@.
  99  *
 100  *              Some additional declarations are made.  As a convenience,
 101  *              @ext__functype@ is the function type of @ext@.  Declarations
 102  *              are made for @pick@ and @dflt@, as @static@ functions.
 103  */
 104
 105 #ifdef CPU_DISPATCH_P
 106
 107 #define CPU_DISPATCH(stcls, rtn, ret, ext, argdecls, args, pick, dflt)  \
 108                                                                         \
 109 typedef ret ext##__functype argdecls;                                   \
 110 static ret dflt argdecls;                                               \
 111 static ret ext##__dispatch argdecls;                                    \
 112 static ext##__functype *pick(void);                                     \
 113 static ext##__functype *ext##__ptr = ext##__dispatch;                   \
 114                                                                         \
 115 static ret ext##__dispatch argdecls                                     \
 116 {                                                                       \
 117   ext##__functype *f = pick();                                          \
 118   DISPATCH_STORE(ext##__ptr, f);                                        \
 119   rtn f args;                                                           \
 120 }                                                                       \
 121                                                                         \
 122 stcls ret ext argdecls                                                  \
 123 {                                                                       \
 124   ext##__functype *f;                                                   \
 125   DISPATCH_LOAD(ext##__ptr, f);                                         \
 126   rtn f args;                                                           \
 127 }
 128
 129 #else
 130
 131 #define CPU_DISPATCH(stcls, rtn, ret, ext, argdecls, args, pick, dflt)  \
 132                                                                         \
 133 typedef ret ext##__functype argdecls;                                   \
 134 static ret dflt argdecls;                                               \
 135 static ext##__functype *pick(void) IGNORABLE;                           \
 136                                                                         \
 137 stcls ret ext argdecls { rtn dflt args; }
 138
 139 #endif
 140
 141 /*----- Functions provided ------------------------------------------------*/
 142
 143 /* --- @cpu_feature_p@ --- *
 144  *
 145  * Arguments:   @unsigned feat@ = a @CPUFEAT_...@ code
 146  *
 147  * Returns:     Nonzero if the feature is available.
 148  */
 149
 150 enum {
 151   CPUFEAT_X86_SSE2,                     /* Streaming SIMD Extensions 2 */
 152   CPUFEAT_X86_AESNI                     /* AES Native Instructions */
 153 };
 154
 155 extern int cpu_feature_p(int /*feat*/);
 156
 157 /*----- That's all, folks -------------------------------------------------*/
 158
 159 #ifdef __cplusplus
 160   }
 161 #endif
 162
 163 #endif