This table gives an overview of how to return results from your assembler routines in Delphi 32-bit applications. The first column lists the different types. The second column shows where such a type is returned. The third column indicates the nature of the returned result.
| Delphi variable type | Returned where? | What? |
ShortInt | al | 8-bit signed value |
SmallInt(1) | ax | 16-bit signed value |
LongInt(2) | eax | 32-bit signed value |
Byte | al | 8-bit unsigned value |
Word | ax | 16-bit unsigned value |
LongWord(3) | eax | 32-bit unsigned value |
Int64 | edx:eax | 64-bit signed value |
Boolean | al | True or False |
ByteBool | al | 8-bit value, non-zero is true |
WordBool | ax | 16-bit value, non-zero is true |
LongBool | eax | 32-bit value, non-zero is true |
Single | ST(0)(4) | 80-bit floating point value |
Double | ST(0)(4) | 80-bit floating point value |
Extended | ST(0)(4) | 80-bit floating point value |
Real48 | ST(0)(4) | 80-bit floating point value |
Comp | ST(0)(4) (5) | 80-bit floating point value |
Currency | ST(0)(4) | 80-bit floating point value(6) |
AnsiChar | al | 8-bit character |
WideChar | ax | 16-bit Unicode character |
AnsiString | Extra var parameter(7) | Pointer to Ansistring pointer |
(tbc) | | |
| |
(1) The SHORT type is the same as SmallInt
(2) The Integer generic type is currently mapped to LongInt
(3) The DWORD and UINT types are the same as Longword. Also, the generic type Cardinal is on the 32-bit platform mapped to a Longword
(4) The FPU registers are all 80-bits. All real results are returned in ST(0). It's only the storage or manipulation afterwards that will define them as single, double, etc.
(5) Even though Comp represents a 64-bit integer, it is a type that is manipulated in the FPU, as opposed to the other integer types, which are manipulated using the CPU. As such, Comp follows the rules for real numbers in terms of manipulation and passing around.
(6) Whole number scaled by 10,000
(7) See Chapter 4 for a detailed explanation.
Source: www.guidogybels.net.