ARM汇编（四）——控制程序流

这一章我们引入条件逻辑——if/then/else语句，以及循环——for和while语句

无条件跳转

B label

标签被解释为当前PC的偏移量

例子：

_start:	MOV X1, #1
	B _start

条件分支

B.{condition} label

循环

基本循环

FOR I = 1 to 10

​ ...some statements...

  MOV W2,#1
loop:	

  ADD W2,W2,#1
  CMP W2,#10
  B.LE	loop

  MOV W2, #10 // R2 holds I
loop: // body of the loop goes here.
  // The CMP is redundant since we
  // are doing SUBS.
  SUBS W2, W2, #1 // I = I - 1
  B.NE loop 

While循环

  // W4 is X and has been initialized
loop: CMP W4, #5
  B.GE loopdone
  // ... other statements in the loop body ...
  B loop
loopdone: // program continues

If/The/Else

  CMP W5, #10
  B.GE elseclause
  ... if statements ...
  B endif
elseclause:
  ... else statements ...
endif: // continue on after the /then/else ...

逻辑运算

AND{S} Xd, Xs, Operand2
EOR{S} Xd, Xs, Operand2
ORR{S} Xd, Xs, Operand2
BIC{S} Xd, Xs, Operand2