CODEWITHSUNDEEP
assembly
Krab
Krab

Reputation: 6756

Assembly - first bit in bit array

I need 2 bits with offset 6 from bit array.

mov eax, [bitarray]; // get address of bit array
shr eax, 6; // clear first 6 bits
shl eax, 30 // clear last 30 bits
shr eax, 30; // move that 2 bits back to start

now in eax is these 2 bits i need, right?

When i have memory started from 0 (one unit is one bit), then bit on position 0 will be after load into register eax in most right place or most left place?

Upvotes: 1

Views: 1009

Answers (2)

ady
ady

Reputation: 173

mov eax, [bitarray]

bitmask?

mov eax,[bitarray]
mov ebx,C0         ;11000000 binary
and ax,bx

Upvotes: 0

Michael
Michael

Reputation: 58427

Instead of the two shifts at the end you could have use a bitwise AND:

AND EAX,3  ; Keep the original value of the two least significant bits; all
           ; other bits in EAX are cleared.

The left-most bit is the most significant one, and the right-most bit the least significant one.

Upvotes: 3

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