Cirrus Logic CS485 Manual de usuario descargar pdf (Pagina 14)

CS485G Spring 2015 14

pushl %ebp # save base pointer

movl %esp,%ebp # new base pointer

pushl %ebx # save old contents of %ebx

movl 8(%ebp), %edx # edx = xp

movl 12(%ebp), %ecx # ecx = yp

movl (%edx), %ebx # ebx =

t0 =

movl (%ecx), %eax # eax =

t1 =

movl %eax, (%edx) #

xp = t1

movl %ebx, (%ecx) #

yp = t0

popl %ebx # restore %ebx

popl %ebp # restore %ebp

ret # return

17 More complex memory-addressing modes

(a) We saw memory and displacement.

(b) This is the most general form: D(Rb,Ri,S)

i. D is the displacement, in bytes, such as 1, 2, 80.

ii. Rb is the base register: any of the 8 integer registers.

iii. Ri is the index register, any register by %esp, and you most

likely don’t want to use %ebp, either

iv. S is a scale, which is any of 1, 2, 4, or 8.

(d) Example

i. %edx: 0xf000

ii. %ecx: 0x0100

iii. 0x8(%edx): 0xf000 + 0x8 = 0xf008

iv. (%edx,%ecx): 0xf000 + 0x0100 = 0xf100

v. (%edx,%ecx,4): 0xf000 + 4

0x0100 = 0xf400

vi. 0x80(,%edx,2): 2

0xf000 + 0x80 = 0x1e080

18 Address computation without referencing

(a) One can compute an address and save it without actually refer-

encing it.

(b) leal src, dest

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Cirrus Logic CS485 Manual de usuario Pagina 14