SDL2.0例子代码分析—代码运行平台检测

SDL2.0例子程序中的 testplatform项目代码分析 ,针对不同的平台 检测字节序 CPU支持的指令集 类型宽度 以及断言

代码+注释

 #include <stdio.h>  #include "SDL.h" #include "SDL_endian.h" #include "SDL_cpuinfo.h" #include "SDL_assert.h"  /*  *  该例子代码检测运行平台  */ //判断变量占用字节数 是否等于 hardcodetype static int badsize(size_t sizeoftype, size_t hardcodetype) {  return sizeoftype != hardcodetype; }   //检测系统是否出现错误类型   貌似用处不大这段坑爹代码  //如果平台类型错误 返回1 否则返回  0 int TestTypes(SDL_bool verbose) {  int error = 0;   //如果Uint8占用一个字节  if (badsize(sizeof(Uint8), 1))  {   //如果Uint8不等于1那么输出 实际占用尺寸    if (verbose)    SDL_Log("sizeof(Uint8) != 1, instead = %u/n",    (unsigned int)sizeof(Uint8));   //错误次数++   ++error;  }  //如如下类似 上述   if (badsize(sizeof(Uint16), 2)) {   if (verbose)    SDL_Log("sizeof(Uint16) != 2, instead = %u/n",    (unsigned int)sizeof(Uint16));   ++error;  }  if (badsize(sizeof(Uint32), 4)) {   if (verbose)    SDL_Log("sizeof(Uint32) != 4, instead = %u/n",    (unsigned int)sizeof(Uint32));   ++error;  }  if (badsize(sizeof(Uint64), 8)) {   if (verbose)    SDL_Log("sizeof(Uint64) != 8, instead = %u/n",    (unsigned int)sizeof(Uint64));   ++error;  }  if (verbose && !error)   SDL_Log("All data types are the expected size./n");   return (error ? 1 : 0); }  //测试尾数  也就是机器的字节序   //windows默认是小端模式  //也就是 低位先存 原因是 堆栈是 由高地址向低地址扩展 int TestEndian(SDL_bool verbose) {  int error = 0;  Uint16 value = 0x1234;  int real_byteorder;  Uint16 value16 = 0xCDAB;  Uint16 swapped16 = 0xABCD;  Uint32 value32 = 0xEFBEADDE;  Uint32 swapped32 = 0xDEADBEEF;  Uint64 value64, swapped64;     //定义64位置 也就是 0x00000000EFBEADDE  value64 = 0xEFBEADDE;  //右移动32位  也就是四个字节  value64 <<= 32;  //将低位置为0xCDAB3412  value64 |= 0xCDAB3412;   //如下操作和value64雷同   swapped64 = 0x1234ABCD;  swapped64 <<= 32;  swapped64 |= 0xDEADBEEF;  //打印机器字节序 是大端模式还是小端模式   if (verbose) {   SDL_Log("Detected a %s endian machine./n",    (SDL_BYTEORDER == SDL_LIL_ENDIAN) ? "little" : "big");  }  //我们自己判断字节序 将value转换为 char类型之后 由于数据丢失 变成了0x34 在windows下低位先存   //所以 左移4位后变成了0x3了  也就是小端口模式  if ((*((char *)&value) >> 4) == 0x1) {   real_byteorder = SDL_BIG_ENDIAN;  }  else {   real_byteorder = SDL_LIL_ENDIAN;  }  //如果我们分析的 真正的字节序不等于 SDL给出的字节序 那么 输出真正的字节序 error++  if (real_byteorder != SDL_BYTEORDER) {   if (verbose) {    SDL_Log("Actually a %s endian machine!/n",     (real_byteorder == SDL_LIL_ENDIAN) ? "little" : "big");   }   ++error;  }  //交换字节序 输出   if (verbose) {   SDL_Log("Value 16 = 0x%X, swapped = 0x%X/n", value16,    SDL_Swap16(value16));  }  //如果交换后的值不等于 0xABCD   if (SDL_Swap16(value16) != swapped16) {   if (verbose) {    SDL_Log("16 bit value swapped incorrectly!/n");   }   ++error;  }  //交换32位高度字节序   if (verbose) {   SDL_Log("Value 32 = 0x%X, swapped = 0x%X/n", value32,    SDL_Swap32(value32));  }  if (SDL_Swap32(value32) != swapped32) {   if (verbose) {    SDL_Log("32 bit value swapped incorrectly!/n");   }   ++error;  }  if (verbose) {     //如果是微软的编译器 也就是VC下 打印出64位的交换字节序之后的值 #ifdef _MSC_VER   SDL_Log("Value 64 = 0x%I64X, swapped = 0x%I64X/n", value64,    SDL_Swap64(value64)); #else     //如果是其他编译器 那么  64位置 ULONG 就需要定义为 unsigned long long 来代表 64位无符号 Integer   SDL_Log("Value 64 = 0x%llX, swapped = 0x%llX/n",    (unsigned long long) value64,    (unsigned long long) SDL_Swap64(value64)); #endif  }  //判断交换后的值是否等于 0x1234ABCDDEADBEEF;  if (SDL_Swap64(value64) != swapped64) {   if (verbose) {    SDL_Log("64 bit value swapped incorrectly!/n");   }   ++error;  }  //返回错误状态  return (error ? 1 : 0); }   //检测CPU 的特性 int TestCPUInfo(SDL_bool verbose) {    if (verbose) {     //打印CPU数量   SDL_Log("CPU count: %d/n", SDL_GetCPUCount());    //获取CPU Cache LIne的大小 即CPU 一次从主存Copy的内存大小   SDL_Log("CPU cache line size: %d/n", SDL_GetCPUCacheLineSize());         //CPU是否支持RDTSC指令 读取时间标签计数器   SDL_Log("RDTSC %s/n", SDL_HasRDTSC() ? "detected" : "not detected");   ///cpu 是否支持 Altivec  AltiVec提供了32个128比特向量暂存器,与之相比,SSE和SSE2只提供了8个   SDL_Log("AltiVec %s/n", SDL_HasAltiVec() ? "detected" : "not detected");   //cpu是否支持 MMX指令    SDL_Log("MMX %s/n", SDL_HasMMX() ? "detected" : "not detected");    //CPU是否支持SIMD ， 由AMD开发的一套SIMD多媒体指令集，支持单精度浮点数的矢量运算，用于增强x86架构的计算机在三维图像处理上的性能   SDL_Log("3DNow! %s/n", SDL_Has3DNow() ? "detected" : "not detected");    //cpu是否支持SSE   SDL_Log("SSE %s/n", SDL_HasSSE() ? "detected" : "not detected");   //SSE2是否支持 如下都是判断CPU是否支持一下加速指令集    SDL_Log("SSE2 %s/n", SDL_HasSSE2() ? "detected" : "not detected");   SDL_Log("SSE3 %s/n", SDL_HasSSE3() ? "detected" : "not detected");   SDL_Log("SSE4.1 %s/n", SDL_HasSSE41() ? "detected" : "not detected");   SDL_Log("SSE4.2 %s/n", SDL_HasSSE42() ? "detected" : "not detected");   SDL_Log("AVX %s/n", SDL_HasAVX() ? "detected" : "not detected");   //获取系统RAM大小 也就是内存大小   SDL_Log("System RAM %d MB/n", SDL_GetSystemRAM());  }  return (0); }  int TestAssertions(SDL_bool verbose) {    //sdl断言  SDL_assert(0);  SDL_assert_release(1);  SDL_assert_paranoid(1);  SDL_assert(0 || 1);  SDL_assert_release(0 || 1);  SDL_assert_paranoid(0 || 1);  #if 0   /* enable this to test assertion failures. */  SDL_assert_release(1 == 2);  SDL_assert_release(5 < 4);  SDL_assert_release(0 && "This is a test"); #endif   {     //获取所有的断言 链表  在调用SDL_GetAssertionReport 之前    /************************************************************************/ /*    typedef struct SDL_assert_data    {    int always_ignore;    unsigned int trigger_count;    const char *condition;    const char *filename;    int linenum;    const char *function;    const struct SDL_assert_data *next;    } SDL_assert_data;                                                                     */   /************************************************************************/   const SDL_assert_data *item = SDL_GetAssertionReport();    //我们发现就是取出所有的 断言结果 输出   while (item) {    SDL_Log("'%s', %s (%s:%d), triggered %u times, always ignore: %s./n",     item->condition, item->function, item->filename,     item->linenum, item->trigger_count,     item->always_ignore ? "yes" : "no");    item = item->next;   }  }  return (0); }  int main(int argc, char *argv[]) {  SDL_bool verbose = SDL_TRUE;  int status = 0;   /* 设置特定日志的优先级 这里是应用程序日志  */  SDL_LogSetPriority(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_INFO);  //如果参数1= -q 那么设置 verbose=faslse  if (argv[1] && (SDL_strcmp(argv[1], "-q") == 0)) {   verbose = SDL_TRUE;  }  if (verbose) {   SDL_Log("This system is running %s/n", SDL_GetPlatform());  }  //测试变量尺寸  status += TestTypes(verbose);  //测试尾数  也就是测试机器的字节序  status += TestEndian(verbose);  //测试CPU信息  status += TestCPUInfo(verbose);  //测试断言  status += TestAssertions(verbose);   return status; } 

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