Intel XENIX 286 Programmers Guide (86) - Tenox.tc

as: A sse m bier XENIX Programming
Based Indexed Operands
Based indexed operands are bytes or words in memory whose addresses are computed by
adding a constant, a base register, and an index register. The operands have the forms
expression ] (bx) (di)
expression ] (bx) (si)
expression ] (bp) (di)
expression ] (bp) (si)
where expression is an absolute expression or a symbol that resolves to an absolute.
Based indexed operands provide a very flexible method of accessing items that require
two address components. For example, elements of multidimensional arrays can be
accessed by setting expression to the start address of the array and assigning the
appropriately scaled index values to the base and index registers.
The following examples illustrate based indexed operands:
movb Darray (bx) (di), * 1
mov ax, (bx) (si)
neg -2 (bp) (si)
Indirect Address Operands
Indirect address operands are instruction addresses stored in memory at given indirect
addresses. Indirect address operands have the form
@expression
where expression is an absolute expression or a symbol that resolves to an absolute.
Indirect address operands may be used only with the calli, call, jmpi, and jmp
instructions. When used with the intersegment call or jump instruction, expression
must point to a 4-byte segment/offset instruction address. When used with the call or
jump instruction, expression must point to a 2-byte offset to an instruction.
The following examples illustrate indirect address operands:
7-22
moncall:
.word
.word
subtest':
.word
.text
examp:
calli
jmp
OFFSET
SEG SELECT
OFFSET
@moncall
@subtest