unit cpusage;

interface

uses windows, messages;

const
 SystemBasicInformation = 0;
 SystemPerformanceInformation = 2;
 SystemTimeInformation = 3;

type
 TPDWord = ^DWORD;

 TSystem_Basic_Information = packed record
   dwUnknown1: DWORD;
   uKeMaximumIncrement: ULONG;
   uPageSize: ULONG;
   uMmNumberOfPhysicalPages: ULONG;
   uMmLowestPhysicalPage: ULONG;
   uMmHighestPhysicalPage: ULONG;
   uAllocationGranularity: ULONG;
   pLowestUserAddress: Pointer;
   pMmHighestUserAddress: Pointer;
   uKeActiveProcessors: ULONG;
   bKeNumberProcessors: byte;
   bUnknown2: byte;
   wUnknown3: word;
 end;

type
 TSystem_Performance_Information = packed record
   liIdleTime: LARGE_INTEGER; {LARGE_INTEGER}
   dwSpare: array[0..75] of DWORD;
 end;

type
 TSystem_Time_Information = packed record
   liKeBootTime: LARGE_INTEGER;
   liKeSystemTime: LARGE_INTEGER;
   liExpTimeZoneBias: LARGE_INTEGER;
   uCurrentTimeZoneId: ULONG;
   dwReserved: DWORD;
 end;

var
 NtQuerySystemInformation: function(infoClass: DWORD;
   buffer: Pointer;
   bufSize: DWORD;
   returnSize: TPDword): DWORD; stdcall = nil;

 liOldIdleTime: LARGE_INTEGER = ();
 liOldSystemTime: LARGE_INTEGER = ();

function GetCPUUsage: Double;

implementation

//------------------------------------------------------------------------------

function Li2Double(x: LARGE_INTEGER): Double;
begin
 Result := x.HighPart * 4.294967296E9 + x.LowPart
end;

//------------------------------------------------------------------------------

function GetCPUUsage: Double;
var
 SysBaseInfo: TSystem_Basic_Information;
 SysPerfInfo: TSystem_Performance_Information;
 SysTimeInfo: TSystem_Time_Information;
 status: Longint; {long}
 dbSystemTime: Double;
 dbIdleTime: Double;
 bLoopAborted: boolean;
begin
 if @NtQuerySystemInformation = nil then
   NtQuerySystemInformation := GetProcAddress(GetModuleHandle('ntdll.dll'),
     'NtQuerySystemInformation');
 if @NtQuerySystemInformation = nil then exit;
 status := NtQuerySystemInformation(SystemBasicInformation, @SysBaseInfo, SizeOf(SysBaseInfo), nil);
 if status <> 0 then exit;

 status := NtQuerySystemInformation(SystemTimeInformation, @SysTimeInfo, SizeOf(SysTimeInfo), 0);
 if status <> 0 then Exit;

 status := NtQuerySystemInformation(SystemPerformanceInformation, @SysPerfInfo, SizeOf(SysPerfInfo), nil);
 if status <> 0 then Exit;

 liOldIdleTime := SysPerfInfo.liIdleTime;
 liOldSystemTime := SysTimeInfo.liKeSystemTime;

 sleep(1000);

 status := NtQuerySystemInformation(SystemTimeInformation, @SysTimeInfo, SizeOf(SysTimeInfo), 0);
 if status <> 0 then Exit;

 status := NtQuerySystemInformation(SystemPerformanceInformation, @SysPerfInfo, SizeOf(SysPerfInfo), nil);
 if status <> 0 then Exit;

 dbIdleTime := Li2Double(SysPerfInfo.liIdleTime) - Li2Double(liOldIdleTime);
 dbSystemTime := Li2Double(SysTimeInfo.liKeSystemTime) - Li2Double(liOldSystemTime);

 dbIdleTime := dbIdleTime / dbSystemTime;

 dbIdleTime := 100.0 - dbIdleTime * 100.0 / SysBaseInfo.bKeNumberProcessors + 0.5;

 result :=  dbIdleTime;
end;

//------------------------------------------------------------------------------

end.

unit Unit1;

interface

uses
 Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
 Dialogs, StdCtrls, cpusage;

type
 TForm1 = class(TForm)
   Button1: TButton;
   Label1: TLabel;
   procedure Button1Click(Sender: TObject);
 private
   { Private declarations }
 public
   { Public declarations }
 end;

var
 Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
 label1.Caption := floattostr(GetCPUUsage);
end;

end.