Mercurial > sdl-ios-xcode

annotate src/thread/dc/SDL_sysmutex.c @ 3880:74e828c64315 SDL-1.2

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Fixed bug #292 I might be on crack here. It looks like SDL_ConvertMono() in src/audio/SDL_audiocvt.c adds the left and right channels of a stereo stream together, and clamps the new mono channel if it would overflow. Shouldn't it be dividing by 2 to average the two sample points instead of clamping? Otherwise the mono sample point's volume doubles in the conversion. This would also make the conversion faster, as it replaces two branches per sample frame with a bitwise shift. --ryan.
author Sam Lantinga <slouken@libsdl.org>
date Sun, 24 Sep 2006 15:45:37 +0000
parents d910939febfa
children 782fd950bd46 c121d94672cb a1b03ba2fcd0
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1 /*
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2 SDL - Simple DirectMedia Layer
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3 Copyright (C) 1997-2006 Sam Lantinga
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4
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5 This library is free software; you can redistribute it and/or
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6 modify it under the terms of the GNU Lesser General Public
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7 License as published by the Free Software Foundation; either
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8 version 2.1 of the License, or (at your option) any later version.
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9
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10 This library is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 Lesser General Public License for more details.
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14
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15 You should have received a copy of the GNU Lesser General Public
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16 License along with this library; if not, write to the Free Software
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17 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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18
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19 Sam Lantinga
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20 slouken@libsdl.org
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21 */
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22 #include "SDL_config.h"
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23
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24 /* An implementation of mutexes using semaphores */
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25
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26 #include "SDL_thread.h"
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27 #include "SDL_systhread_c.h"
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28
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29 #include <arch/spinlock.h>
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30
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31 struct SDL_mutex {
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32 int recursive;
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33 Uint32 owner;
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34 spinlock_t mutex;
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35 };
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36
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37 /* Create a mutex */
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38 SDL_mutex *SDL_CreateMutex(void)
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39 {
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40 SDL_mutex *mutex;
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41
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42 /* Allocate mutex memory */
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43 mutex = (SDL_mutex *)SDL_malloc(sizeof(*mutex));
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44 if ( mutex ) {
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45 spinlock_init(&mutex->mutex);
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46 mutex->recursive = 0;
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47 mutex->owner = 0;
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48 } else {
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49 SDL_OutOfMemory();
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50 }
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51 return mutex;
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52 }
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53
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54 /* Free the mutex */
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55 void SDL_DestroyMutex(SDL_mutex *mutex)
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56 {
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57 if ( mutex ) {
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58 SDL_free(mutex);
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59 }
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60 }
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61
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62 /* Lock the semaphore */
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63 int SDL_mutexP(SDL_mutex *mutex)
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64 {
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65 #if SDL_THREADS_DISABLED
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66 return SDL_arraysize(return ),0;
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67 #else
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68 Uint32 this_thread;
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69
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70 if ( mutex == NULL ) {
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71 SDL_SetError("Passed a NULL mutex");
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72 return -1;
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73 }
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74
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75 this_thread = SDL_ThreadID();
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76 if ( mutex->owner == this_thread ) {
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77 ++mutex->recursive;
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78 } else {
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79 /* The order of operations is important.
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80 We set the locking thread id after we obtain the lock
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81 so unlocks from other threads will fail.
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82 */
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83 spinlock_lock(&mutex->mutex);
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84 mutex->owner = this_thread;
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85 mutex->recursive = 0;
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86 }
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87
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88 return 0;
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89 #endif /* SDL_THREADS_DISABLED */
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90 }
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91
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92 /* Unlock the mutex */
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93 int SDL_mutexV(SDL_mutex *mutex)
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94 {
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95 #if SDL_THREADS_DISABLED
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96 return 0;
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97 #else
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98 if ( mutex == NULL ) {
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99 SDL_SetError("Passed a NULL mutex");
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100 return -1;
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101 }
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102
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103 /* If we don't own the mutex, we can't unlock it */
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104 if ( SDL_ThreadID() != mutex->owner ) {
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105 SDL_SetError("mutex not owned by this thread");
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106 return -1;
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107 }
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108
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109 if ( mutex->recursive ) {
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110 --mutex->recursive;
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111 } else {
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112 /* The order of operations is important.
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113 First reset the owner so another thread doesn't lock
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114 the mutex and set the ownership before we reset it,
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115 then release the lock semaphore.
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116 */
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117 mutex->owner = 0;
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118 spinlock_unlock(&mutex->mutex);
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119 }
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120 return 0;
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121 #endif /* SDL_THREADS_DISABLED */
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122 }