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  Using Bit Fields
  Submitted by



A way to save memory is to use flag, here i little tips to make cleaner code

To store flag data like this way is to AVOID

// Structure that content most important cpu informations
// (avoid)
typedef struct CPUINFO2
{
 char* pszProcessor; // CPU Processor string
 char* pszVendor;    // CPU vendor name string

 bool bHasCPUID;     // Supports CPUID instruction
 bool bHasFPU;       // FPU present
 bool bHasVME;       // Virtual Mode Extensions
 bool bHasDebug;     // Debug extensions
 bool bHasPSE;       // Page Size Extensions
 bool bHasTSC;       // Time Stamp Counter
 bool bHasMSR;       // Model Specific Registers
 bool bHasPAE;       // Page Address Extensions
 bool bHasMCE;       // Machine Check Extensions
 bool bHasCMPXCHG8;  // CMPXCHG8 instruction
 bool bHasAPIC;      // APIC
 bool bHasSysCenter; // SYSENTER/SYSEXIT instruction
 bool bHasMTRR;      // Memory Type Range Registers
 bool bHasGPE;       // Global Paging Extensions
 bool bHasMCA;       // Machine Check Architecture
 bool bHasCMOV;      // CMOV instruction
 bool bHasPAT;       // Page Attribue Table
 bool bHasPSE36;     // PSE36 (Page Size Extensions)
 bool bHasMMXExt;    // MMX Extensions
 bool bHasMMX;       // MMX support
 bool bHasFXSave;    // FXSAVE/FXRSTOR instruction
 bool bHas3DNowExt;  // Extended 3DNow! support
 bool bHas3DNow;     // 3DNow! support
 bool bHasSSEMMX;    // SSE MMX support (same as MMXEXT)
 bool bHasSSE;       // SSE
 bool bHasSSEFP;     // SSE FP support
} CPUINFO2, *LPCPUINFO2; 



Why? using a byte for each flag make the struct consume memory as well

The solution is to use flag stored on a single data like byte , word or dword but the old way like that is not the prefered one:

remove flag:
dwFlags &= ~MYFLAG

Set flag:
dwFlags |= MYFLAG

Is flag:
if( dwFlags & MYFLAG )

By using bit field we can make cleaner code and using same memory as old flag way....

example:

// Structure that content most important cpu informations
// (prefered)
typedef struct CPUINFO
{
 char* pszProcessor;    // CPU Processor string
 char* pszVendor;       // CPU vendor name string

 struct
 {
  DWORD bHasCPUID     : 1; // Supports CPUID instruction
  DWORD bHasFPU       : 1; // FPU present
  DWORD bHasVME       : 1; // Virtual Mode Extensions
  DWORD bHasDebug     : 1; // Debug extensions
  DWORD bHasPSE       : 1; // Page Size Extensions
  DWORD bHasTSC       : 1; // Time Stamp Counter
  DWORD bHasMSR       : 1; // Model Specific Registers
  DWORD bHasPAE       : 1; // Page Address Extensions
  DWORD bHasMCE       : 1; // Machine Check Extensions
  DWORD bHasCMPXCHG8  : 1; // CMPXCHG8 instruction
  DWORD bHasAPIC      : 1; // APIC
  DWORD bHasSysCenter : 1; // SYSENTER/SYSEXIT instruction
  DWORD bHasMTRR      : 1; // Memory Type Range Registers
  DWORD bHasGPE       : 1; // Global Paging Extensions
  DWORD bHasMCA       : 1; // Machine Check Architecture
  DWORD bHasCMOV      : 1; // CMOV instruction
  DWORD bHasPAT       : 1; // Page Attribue Table
  DWORD bHasPSE36     : 1; // PSE36 (Page Size Extensions)
  DWORD bHasMMXExt    : 1; // MMX Extensions
  DWORD bHasMMX       : 1; // MMX support
  DWORD bHasFXSave    : 1; // FXSAVE/FXRSTOR instruction
  DWORD bHas3DNowExt  : 1; // Extended 3DNow! support
  DWORD bHas3DNow     : 1; // 3DNow! support
  DWORD bHasSSEMMX    : 1; // SSE MMX support (same as MMXEXT)
  DWORD bHasSSE       : 1; // SSE
  DWORD bHasSSEFP     : 1; // SSE FP support
 };
} CPUINFO, *LPCPUINFO; 

All states using bHas... is a single bit, not a byte or doubleword only bit
Note you can change for any bit as you want but the maximum of the struct must be 32 (dword) as well..

// Size of the struct CPUINFO is 12
// Size of the struct CPUINFO2 is 36

Hope you like it!




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