Pointers and references: Difference between revisions
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→{{header|68000 Assembly}}: used code tags for better style
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dc.b $80,$81,$82,$83</lang>
The
This isn't needed for values in RAM, but it is needed for loading from data tables in ROM.
<lang 68000devpac>LEA myData,A0 ;address of myData is stored in A0</lang>
The address registers <code>A0
68000 Assembly doesn't care about what type of data is being pointed to. It makes no distinction between bytes, words, longs, or executable code. That is up to the opcodes that interact with the data. For the following, assume that the address
<lang 68000devpac>MOVE.B (A0),D0 ;D0 = 0x00000080
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MOVE.L (A0),D0 ;D0 = 0x80818283</lang>
Putting a + after <code>(A0)</code> auto-increments the pointer by 1,2,or 4 for <code>MOVE.B</code>,
<lang 68000devpac>LEA myData,A0 ;Assume for this example that data registers all equal 0.
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Putting a - before <code>(A0)</code> pre-decrements the pointer by 1,2, or 4 for <code>MOVE.B</code>,
<lang 68000devpac>LEA myData+4,A0 ;Assume for this example that data registers all equal 0.
MOVE.B -(A0),D0 ;D0 = 00000083
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MOVE.B -(A0),D2 ;D2 = 00000081</lang>
<code>LEA</code> can also be used to pre-calculate a complex offset to an address.
<lang 68000devpac>LEA myData,A0
MOVE.W #$0C,D0
LEA (4,A0,D0),A3</lang> ;A3 = address of myData + 4 + $0C
An address can be offset by an immediate value, a register, or both. Data register offsets are measured at 16 bit word length. Although the second <code>LEA</code> is in brackets, it does NOT dereference the pointer. Let's look at the following example data:
<lang 68000devpac>myPointers: dc.l myData, myData2
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<lang 68000devpac>MOVE.L #$FFEEDDCC,myVar</lang>
There is nothing stopping you from clobbering nearby stored data. In the above example, the byte FF gets written to $100000, EE to $100001, DD to $100002, and CC to $100003. If you intended myVar to be of byte length, you need to make sure you only use MOVE.B to read
=={{header|Ada}}==
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