This table gives an overview of how parameters are passed. A distinction is made between passing by value, as const or by reference. The "Value can be passed in a register?" column indicates whether or not a specific type qualifies for passing in a register if it is passed as a value (applicable only to the "By Value" and "Const" columns!). Passing by reference in the form of a 32-bit pointer always qualifies for passing in a register obviously. This is possible for all types, except method pointers that are always passed on the stack. For example, an int64 type does not qualify according to the table below for passing in register when it is passed as a value. However, since passing it by reference means passing a 32-bit pointer to the int64 value, when you pass an int64 by reference, this does qualify for using a register.

⁽¹⁾ These types that occupy less than 32-bits will still take up 32-bits. The actual value is stored in the lowest parts of the stack location or register and the content of the remaining part is undefined and should be treated as such at all times.
⁽²⁾ The pointer points to the lowest dword of the value. The highest dword is stored in the next dword.
⁽³⁾ Method pointers are always passed on the stack. They consist of an instance pointer, which is pushed before the actual method pointer, which means the method pointer sits on the lowest address on the stack.
⁽⁴⁾ If the Set contents fit into a byte/word/dword, its value is passed immediately, respectively as a 8/16/32 bit value. Otherwise, a 32-bit pointer to the set is passed.
⁽⁵⁾ If the record contents fit into a byte/word/dword, the data is passed immediately, respectively as a 8/16/32 bit value. Otherwise, a 32-bit pointer to the record is passed.
⁽⁶⁾ If the array contents fit into a byte/word/dword, the data is passed immediately, respectively as a 8/16/32 bit value. Otherwise, a 32-bit pointer to the array is passed.
⁽⁷⁾ Open arrays are passed as 2 parameters: the first one is the pointer to the actual array, the second one is the number of elements in the array. As such, passing an open array parameter actually occupies 2 parameter positions. For instance: if you use the register calling convention and you pass one open array parameter eax will contain the pointer to the array and edx will contain the number of elements. See Chapter 2 for details about calling conventions. Also note that open array parameters reside on the stack, so refrain from using very large arrays.
⁽⁸⁾ While the value itself occupies only 10 bytes, 12 bytes are actually allocated (3 dwords). The content of the last 2 bytes should be considered undefined.

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