Why do you use #ifndef IN #define IN in C language?

#ifndef OUT
#define OUT
#endif

#ifndef IN
#define IN
#endif

//*********************************************************************************************************************************
// o SHA256_Process() : A function that calls a compression function by dividing an input message with an arbitrary length into 512-bit blocks
// o Input : Pointer variable of Info - SHA-256 structure
//                        pszMessage - Pointer variables for input messages
//                        uDataLen - byte length of input message
// o Output: 
//*********************************************************************************************************************************
void SHA256_Process( OUT SHA256_INFO *Info, IN const BYTE *pszMessage, IN UINT uDataLen ) 
{
    if ((Info->uLowLength += (uDataLen << 3)) < 0)
        Info->uHighLength++;

    Info->uHighLength += (uDataLen >> 29);

    while (uDataLen >= SHA256_DIGEST_BLOCKLEN)
    {
        memcpy((UCHAR_PTR)Info->szBuffer, pszMessage, (SINT)SHA256_DIGEST_BLOCKLEN);
        SHA256_Transform((ULONG_PTR)Info->szBuffer, Info->uChainVar);
        pszMessage += SHA256_DIGEST_BLOCKLEN;
        uDataLen -= SHA256_DIGEST_BLOCKLEN;
    }

    memcpy((UCHAR_PTR)Info->szBuffer, pszMessage, uDataLen);
}