Resize Memory Block

Changes the size of a memory block that was previously allocated with either the Allocate Memory Block function (Int 31H Function 0501H) or the Allocate Linear Memory Block function (Int 31H Function 0504H).

Call With

AX = 0503H
BX:CX = new size of block (bytes, must be nonzero)
SI:DI = memory block handle

Returns

if function successful
Carry flag = clear
BX:CX = new linear address of memory block
SI:DI = new handle for memory block

if function unsuccessful
Carry flag = set
AX = error code

8012H linear memory unavailable

8013H physical memory unavailable

8014H backing store unavailable

8016H handle unavailable

8021H invalid value (BX:CX = 0)

8023H invalid handle (in SI:DI)

Notes

After this function returns, the previous handle for the memory block is invalid and should not be used.
When increasing the size of a block, this function always creates committed pages. When decreasing the block size, this call will correctly free all possible page types (committed pages, uncommitted pages, and mapped pages). The linear address and handle of the memory block may change as a result of this call.
It is the client's responsibility to update any descriptors that map the memory block with the new linear address after resizing the block.
This function returns an error if the client attempts to resize a memory block to zero bytes.

8012H	linear memory unavailable
8013H	physical memory unavailable
8014H	backing store unavailable
8016H	handle unavailable
8021H	invalid value (BX:CX = 0)
8023H	invalid handle (in SI:DI)