low32

[Ficko]

I see that MASM understands "LOW32" as well but how to use it.
I can't manage to declare a constant bigger than DWORD.  ::)

Code Select Expand


.686p
.model flat, stdcall
option casemap :none
Val     EQU     12345678h
;Val     EQU     112345678h ;Error too big
.code
start:
mov eax, low32 Val
nop
end start


[dedndave]

i think EQUates are traditionally limited to the machine width
as i recall, with old versions of MASM (5 and earlier), it had to resolve to a 16-bit integer

[jj2007]

mov eax, low32 (Val*12345678h) works.

[dedndave]

oh - i suppose you could use TEXTEQU and have it resolve to other sizes   :P
or, as in Jochen's example...

Code Select Expand

MyConst TEXTEQU <low32 (Val*12345678h)>
        mov     eax,MyConst

[qWord]

masm use internal 64Bit arithmetic for calculations on constants, but it can only emit 32Bit constants.

[Ficko]

All right I guess since there is no "high32" anyway it is just a "dead end" command. :bg

[MichaelW]

Perhaps is has something to do with 64-bit initializers. Even MASM 5.1 would allow statements like:

xxx dq 1234567812345678h

[dedndave]

yah - but defining data is different than using EQUates for constants
thing is - there aren't very many (single) 32-bit instructions that allow use of 64-bit constants
the EQUates "mechanism" wasn't really designed with SSE in mind

[GregL]

All right I guess since there is no "high32" anyway it is just a "dead end" command. BigGrin

But, there is a HIGH32    (in later versions).

[clive]

Well crap, both of these seem totally useless.

Code Select Expand

Microsoft (R) Macro Assembler Version 10.00.30319.01     07/06/10 13:53:46
...
        push    high32 400921FB54442D18h ; PI
test27.asm(23) : error A2084:constant value too large
        push    low32  400921FB54442D18h
test27.asm(24) : error A2084:constant value too large


[GregL]

Clive,

Try

Code Select Expand


push HIGH32(400921FB54442D18h) ; PI
push LOW32(400921FB54442D18h)


[Edit] Oops, I guess not.

Here are some macros I wrote for the earlier versions of MASM.  I thought they worked the same as the ones in MASM 8.0 and later, I guess not.

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; ====================================
; MASM 8.0 has a macro with the same name and function built in
LOW32 MACRO Q:REQ
    lea edx, Q
    mov eax, DWORD PTR [edx]
    EXITM <eax>
ENDM
; ====================================
; MASM 8.0 has a macro with the same name and function built in
HIGH32 MACRO Q:REQ
    lea edx, Q
    mov eax, DWORD PTR [edx+4]
    EXITM <eax>
ENDM



I'm trying to figure out what LOW32 and HIGH32 in MASM 8.0 and later are good for.

[GregL]

mov eax, low32 (Val*12345678h) works.

I get error A2026: constant expected on that one.  I'm using ML 10.0.

[Edit] OK, I see what he means, the following works.

Code Select Expand


mov eax, LOW32(20*12345678h)


[clive]

Greg,

I'd tried a bunch of combinations, MASM just doesn't like direct input of constants bigger than 32-bits.

Here's what I finally got to work, but I still don't feel Microsoft really understands the point of these functions.

-Clive

Code Select Expand

Microsoft (R) Macro Assembler Version 10.00.30319.01     07/06/10 15:49:16
test27.asm      Page 1 - 1


        .686
        .MODEL FLAT

= 3.141592653589793238 PI      EQU     3.141592653589793238

00000000         .DATA

00000000  40490FDB         REAL4   PI
00000004  400921FB54442D18         REAL8   PI

00000000         .CODE

= 54442D18 _PI    EQU     ((400921FBh SHL 32) + (54442D18h)) ; PI

00000000 _start:

00000000  68 400921FB         push    high32 _PI
00000005  68 54442D18         push    low32  _PI

0000000A  C3         ret

        end         _start


[qWord]

as said, masm internally use 64bit arithmetic. The only way I currently see is to 'calculate' the 64Bit constant from two 32Bit ones:

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foo = (0cccccccch SHL 32) OR (0aaaaaaaah)
.radix 16
%echo @CatStr(%(HIGH32 foo),<_>,%(LOW32 foo))
.radix 10
:bg

[drizz]

masm language could definitely be improved in this area.

not accepting constants for qword,real4,real8 arguments is just annoying.

myproc1 proc qw1:qword,r41:real4,r41:real8
   ret
myproc1 endp

   invoke myproc1,1,2.0,3.0


just for fun:

Code Select Expand

pushR8 macro r8:req
dq r8
org $-8
db 3 dup(02eh), 68h
org $+4
db 68h
dq r8
org $-4
endm

PI      EQU     3.141592653589793238

pushR8 PI