times vs dup? And ' symbol?

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Roman

Joined: 21 Apr 2012
Posts: 1822

Roman 20 Jan 2021, 12:02

What is times and dup differents ?

Code:

times 16 db 0x0f
db 16 dup (0x0f)

What is this mean ?

Code:

dq 0F0F0F0F'0F0F0F0Fh

I am about symbol ' in hex value

20 Jan 2021, 12:02

Calanor

Joined: 19 Jul 2015
Posts: 45
Location: Sweden

Calanor 20 Jan 2021, 13:21

Regarding the second question, in this particular context a single quote can be used as a separator to increase readability. A value expressed as "10'000" is simply treated as 10000. I'd actually forgotten about this feature until your post reminded me! Smile

20 Jan 2021, 13:21

Roman

Joined: 21 Apr 2012
Posts: 1822

Roman 20 Jan 2021, 15:12

O !
times 2000 nop
Do repeat 2000 asm command nop !
As rept 2000 { nop }

Some times its usefull.

20 Jan 2021, 15:12

Calanor

Joined: 19 Jul 2015
Posts: 45
Location: Sweden

Calanor 20 Jan 2021, 15:33

Well, yes, "times" can be useful. I don't know exactly what goes on behind the scenes when it comes to "times" vs "dup", although I presume that using the former to create data would result in longer compilation times than when using the latter.

20 Jan 2021, 15:33

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20421
Location: In your JS exploiting you and your system

revolution 20 Jan 2021, 22:32

Calanor wrote:

... I presume that using the former to create data would result in longer compilation times than when using the latter.

Test it.

20 Jan 2021, 22:32

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8356
Location: Kraków, Poland

Tomasz Grysztar 21 Jan 2021, 09:13

Roman wrote:

What is times and dup differents ?
Code:
times 16 db 0x0f
db 16 dup (0x0f)
    

There is no substantial difference when these constructs are used like here, they differ in how you can use them with other things. First, you can put a label before DB that would be automatically considered a label for a byte-sized data, while TIMES cannot be labeled - you can put a label followed by ":" before it, but this works the same as with any other instruction and is not considered related to the statement that follows. So to make the same kind of label for a TIMES statement you'd need to use additional directive:

Code:

buffer db 16 dup 0x0f

label buffer:byte
times 16 db 0x0f

Also, DUP works only with data values, while TIMES can be used with any instructions (it is more or less just a shortened single-line form of REPEAT).

Roman wrote:

What is this mean ?
Code:
dq 0F0F0F0F'0F0F0F0Fh    
I am about symbol ' in hex value

Both the ` and _ (single quote and underscore) can be used to separate the digits in numbers. This is a purely visual aid, you can use it to group the digits to emphasize their positions and counts (for example to mark bit fields), or just to make a number easier to read.

21 Jan 2021, 09:13

Roman

Joined: 21 Apr 2012
Posts: 1822

Roman 21 Jan 2021, 10:09

Thanks Tomasz.

What is this and what is mean ?
label buffer:byte

I compile this in code.

Code:

.code:
Start:
       mov     eax, buffer
label buffer:byte

IDA Pro show eax = address buffer
Like simple label.

Code:

.code:
Start:
       mov     eax, lb1
lb1:

But what magicaly in buffer:byte ?

21 Jan 2021, 10:09

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8356
Location: Kraków, Poland

Tomasz Grysztar 21 Jan 2021, 10:28

Compare this:

Code:

buffer:
db 0

mov [buffer],1   ; Error: operand size not specified
add [buffer],ax  ; add word [buffer],ax

Code:

buffer db 0

mov [buffer],1   ; mov byte [buffer],1
add [buffer],ax  ; Error: operand sizes do not match

And analogously:

Code:

label buffer

mov [buffer],1   ; Error: operand size not specified
add [buffer],ax  ; add word [buffer],ax

Code:

label buffer:byte

mov [buffer],1   ; mov byte [buffer],1
add [buffer],ax  ; Error: operand sizes do not match

21 Jan 2021, 10:28

Calanor

Joined: 19 Jul 2015
Posts: 45
Location: Sweden

Calanor 21 Jan 2021, 12:49

revolution wrote:

Test it.

Yeah, I did a simple test and not surprisingly "dup" is considerably faster. On my machine, "times 200000000 db 100" (for those who don't want to count the 0's: 200 million) took 5.4 seconds to compile, while "db 200000000 dup 100" required 2.2 seconds. Adding parenthesis after the "dup" (i.e. "dup (100)") increased the time to 2.4 seconds.

As a side-note, one noteworthy difference between using "times" and "rept" is that "times" won't generate a truckload of lines, while "rept" does.

21 Jan 2021, 12:49

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20421
Location: In your JS exploiting you and your system

revolution 21 Jan 2021, 12:55

Calanor: Good.

BTW: There is also repeat.

21 Jan 2021, 12:55

Roman

Joined: 21 Apr 2012
Posts: 1822

Roman 21 Jan 2021, 14:18

Tomasz.
I try this.

Code:

    
     mov [.buffer],1 ;this put byte 
     jmp lp1
label .buffer:byte
lp1:
     mov [.buffer],1 ;this put dword 
label .buffer:dword

Its cool !
How change dynamicly from label buffer:dword to label buffer:word ?

Code:

.data
buffer rb 4000
.code
   mov [buffer],1
   mov [buffer+1],2
;now i want write dword in buffer
buffer:dword
   mov [buffer],1
   mov [buffer+4],2

Its be nice and usefull.
For fill structs or buffers.

21 Jan 2021, 14:18

Roman

Joined: 21 Apr 2012
Posts: 1822

Roman 25 Jan 2021, 12:13

' and _ not work in float values.

Code:

mov dword [val],48_828_125.0 ;error reserved word used as symbol
mov dword [val],48_828_125f ;error reserved word used as symbol

mov dword [val],48'828'125.0 ;error reserved word used as symbol
mov dword [val],48'828'125f ;error reserved word used as symbol

25 Jan 2021, 12:13

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8356
Location: Kraków, Poland

Tomasz Grysztar 25 Jan 2021, 12:54

They do with fasmg.

25 Jan 2021, 12:54

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