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Inside Macintosh: Memory /

Chapter 2 - Memory Manager / Memory Manager Reference

Memory Manager Routines / Changing the Sizes of Relocatable and Nonrelocatable Blocks

GetHandleSize

You can use the GetHandleSize function to find out the logical size of the relocatable block corresponding to a handle.

FUNCTION GetHandleSize (h: Handle): Size;

h

A handle to a relocatable block.

DESCRIPTION

The GetHandleSize function returns the logical size, in bytes, of the relocatable block whose handle is h. In case of an error, GetHandleSize returns 0.

ASSEMBLY-LANGUAGE INFORMATION

The registers on entry and exit for GetHandleSize are

Registers on entry
A0	Handle to the relocatable block

Registers on exit
D0	If >=0, number of bytes in relocatable block
	If <0, result code

The trap dispatcher sets the condition codes before returning from a trap by testing the low-order word of register D0 with a TST.W instruction. Because the block size returned in D0 by _GetHandleSize is a full 32-bit long word, the word-length test sets the condition codes incorrectly in this case. To branch on the contents of D0, use your own TST.L instruction on return from the trap to test the full 32 bits of the register.

SPECIAL CONSIDERATIONS

You shouldn't call GetHandleSize at interrupt time because the heap might be in an inconsistent state.

RESULT CODES

noErr	0	No error
nilHandleErr	-109	NIL master pointer
memWZErr	-111	Attempt to operate on a free block