| layout | title | permalink |
|---|---|---|
page |
Q27835: Operator "." and the Operator "*" |
/pubs/pc/reference/microsoft/kb/Q27835/ |
Article: Q27835
Version(s): 5.10
Operating System: MS-DOS
Flags: ENDUSER | buglist5.10
Last Modified: 27-MAY-1988
Problem:
I am using indirect addressing in the following Microsoft Macro
Assembler instruction (the variable "esi" is a structure variable and
"eax" is a 386 register):
mov eax,[eax.esi*2]
The opcodes generated by MASM indicate that MASM is not using
indirect addressing.
Response:
The problem occurs because the "." operator has a higher precedence
than the "*" operator. MASM turns "[eax.esi*2]" into "[(eax+esi)*2]"
as a result of the precedence. MASM evaluates "(eax+esi)" as a
constant instead of a register; eax being used with a structure
variable, esi. Thus, the result of the constant expression "(eax+esi)"
is multiplied by two and the address mode is lost.
A workaround is to use the "+" operator which has lower precedence
and produces the correct result. The "." operator should be reserved
for structure field names as documented.
Microsoft will correct the problem in a future release.