6、汇编语言编程中的控制流、逻辑运算与内存操作

汇编语言编程中的控制流、逻辑运算与内存操作

1. 循环结构

在汇编语言中，循环结构是实现重复操作的重要手段，常见的循环类型有 FOR 循环和 WHILE 循环。

1.1 FOR 循环

FOR 循环有正向计数和反向计数两种实现方式。

正向计数示例：

MOV R2, #1 @ R2 holds I
loop: @ body of the loop goes here.
      @ Most of the logic is at the end
      ADD R2, #1        @ I = I + 1
      CMP R2, #10
      BLE loop          @ IF I <= 10 goto loop

此代码实现了从 1 到 10 的循环。

反向计数示例：

MOV R2, #10 @R2 holds I
loop: @ body of the loop goes here.
      @ The CMP is redundant since we
      @ are doing SUBS.
      SUBS  R2, #1     @ I = I -1
      BNE   loop       @ branch until I = 0

反向计数时使用 SUBS 指令可节省一条 CMP 指令。

1.2 WHILE 循环