Parameter Passing: Difference between revisions
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Parameters are typically passed via the stack or through registers. For human-written assembly, the programmer can pass an argument by reference by passing a pointer to the argument rather than the argument itself. Of course, the function will need to dereference that pointer; however whether the function writes back the new value to that memory address is also decided by the programmer. This means that just because a parameter is passed by reference does not mean that it gets altered by the function that received it. This (contrived) example shows this concept in action. |
Parameters are typically passed via the stack or through registers. For human-written assembly, the programmer can pass an argument by reference by passing a pointer to the argument rather than the argument itself. Of course, the function will need to dereference that pointer; however whether the function writes back the new value to that memory address is also decided by the programmer. This means that just because a parameter is passed by reference does not mean that it gets altered by the function that received it. This (contrived) example shows this concept in action. |
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<syntaxhighlight lang="68000devpac"> |
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MOVE.L #$00FF0000,D0 ;load D0 with the pointer 0x00FF0000 (I decided this was a pointer just for example's sake.) |
MOVE.L #$00FF0000,D0 ;load D0 with the pointer 0x00FF0000 (I decided this was a pointer just for example's sake.) |
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MOVE.L D0,-(SP) ;push that value onto the stack. |
MOVE.L D0,-(SP) ;push that value onto the stack. |
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MOVE.L (A0),D1 ;dereference the pointer (we're treating it as a pointer to an int) |
MOVE.L (A0),D1 ;dereference the pointer (we're treating it as a pointer to an int) |
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ADD.L D1,D0 ;add the values. |
ADD.L D1,D0 ;add the values. |
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RTS ;and return |
RTS ;and return |
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</syntaxhighlight> |
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===Example [[Ada]]=== |
===Example [[Ada]]=== |
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