ULONG64 on 32 bit machine

unsigned __int64 var64 = 100;

How to access lower and higher order DWORD in var64?

We can use below mentioned structure.

typedef union _ULARGE_INTEGER {
struct {
DWORD LowPart;
DWORD HighPart;
};
struct {
DWORD LowPart;
DWORD HighPart;
} u;
ULONGLONG QuadPart;
} ULARGE_INTEGER;

ULARGE_INTEGER largeVar = 0;

largeVar.QuadPart = var64;

Now you can access.
DWORD LowPart = largeVar.LowPart;
DWORD HighPart = largeVar.HighPart;

These structure can be found at WinNT.h

How LONG64 is stored on stack?

First higher order DWORD is pushed and then lower order DWORD.

code snippet:

unsigned __int64 var = 10;
ULARGE_INTEGER value;
value.QuadPart = var;
value.LowPart = 60;
value.HighPart = 70;


unsigned __int64 var = 10;
00031036 mov dword ptr [var],0Ah
0003103D mov dword ptr [ebp-0Ch],0
ULARGE_INTEGER value;
value.QuadPart = var;
00031044 mov eax,dword ptr [var]
00031047 mov dword ptr [value],eax
0003104A mov ecx,dword ptr [ebp-0Ch]
0003104D mov dword ptr [ebp-4],ecx
value.LowPart = 60;
00031050 mov dword ptr [value],3Ch
value.HighPart = 70;
00031057 mov dword ptr [ebp-4],46h


stack view

0x0019FCEC 0000000a //lower local param1
0x0019FCF0 00000000 //higher local param1
0x0019FCF4 0000003c //lower local param2
0x0019FCF8 00000046 // higher local param2
0x0019FCFC 0019fd40 // ebp