.data
l dw (2)
r dw (3)
.code
start:
mov AX, l
mov BX, r
shr BX, 1
mov CX, AX
shl CX, 15
shr AX, 1
or BX, CX
shl EAX, 16
or AX, BX
end start
i am just about start lerning masm.
can anybody tell me what has the code above done and how?
thx
.data
l dw 2
r dw 3
.code
start: mov ax,l ;AX = l (L)
mov bx,r ;BX = r (R)
shr bx,1 ;BX = R shifted right by 1 bit (1 bit discarded)
mov cx,ax ;CX = AX = L
shl cx,15 ;CX = L shifted left by 15 bits (15 bits discarded)
shr ax,1 ;AX = L shifted right by 1 bit (1 bit discarded)
or bx,cx ;BX = R shifted right by 1 bit (OR) L shifted left by 15 bits
shl eax,16 ;high word = L shifted right by 1 bit
or ax,bx ;low word = R shifted right by 1 bit (OR) L shifted left by 15 bits
;need some kind of termination code here
;different for 16-bit and 32-bit programs
end start
AX 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0
L15 L14 L13 L12 L11 L10 L09 L08 L07 L06 L05 L04 L03 L02 L01 L00
BX 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1
R15 R14 R13 R12 R11 R10 R09 R08 R07 R06 R05 R04 R03 R02 R01 R00
result
EAX 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
0 L15 L14 L13 L12 L11 L10 L09 L08 L07 L06 L05 L04 L03 L02 L01 L00 R15 R14 R13 R12 R11 R10 R09 R08 R07 R06 R05 R04 R03 R02 R01
shorter code...
mov ax,l ;AX = L
shl eax,16 ;high word = L
mov ax,r ;AX = R
shr eax,1