[Beginner] Instruction LEA

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Linasm

Joined: 13 Nov 2004
Posts: 2

Linasm 03 Dec 2004, 13:37

How I use instruction LEA? I would like a very simple example for fasm.

03 Dec 2004, 13:37

vbVeryBeginner

Joined: 15 Aug 2004
Posts: 884
Location: \\world\asia\malaysia

vbVeryBeginner 03 Dec 2004, 19:44

test1 db 'this is string',0

lea eax,[test1]

store the address of test1 into eax

03 Dec 2004, 19:44

vbVeryBeginner

Joined: 15 Aug 2004
Posts: 884
Location: \\world\asia\malaysia

vbVeryBeginner 03 Dec 2004, 19:51

which is equal to
mov eax,test1

03 Dec 2004, 19:51

scientica
Retired moderator

Joined: 16 Jun 2003
Posts: 689
Location: Linköping, Sweden

scientica 03 Dec 2004, 21:17

another usage is to calculate the address of an element in an array:

Code:

lea eax, [ebx+ecx*4]

where ebx is the "base address" (first element)
ecx the index, the 4 is because the array in this example is made up of dwords

lea means "load effective address"

03 Dec 2004, 21:17

Madis731

Joined: 25 Sep 2003
Posts: 2139
Location: Estonia

Madis731 03 Dec 2004, 22:04

I know another use for LEA Very Happy

Code:

mov eax,15 ;eax=15
lea eax,[eax*4+eax] ; eax=75
lea eax,[eax*8+eax] ; eax=675
...
;or edi=esi<<3-edx
lea edi,[esi*8-edx]
...
;or eax=4*ebx+ecx-24
lea eax,[4*ebx+ecx-24]
;USE your imagination, but caution - this instruction
;is long and penalty might occur

03 Dec 2004, 22:04

Nikolay Petrov

Joined: 22 Apr 2004
Posts: 101
Location: Bulgaria

Nikolay Petrov 05 Dec 2004, 15:09

Madis is a good simple Smile

05 Dec 2004, 15:09

Linasm

Joined: 13 Nov 2004
Posts: 2

Linasm 07 Dec 2004, 02:55

Thanks for help-me. Very Happy

07 Dec 2004, 02:55

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