leal运用实例

1.示例1（leal用于计算）

这里使用C语言和汇编代码对比

int arith(int x,int y, int z){
  int t1 = x+y;
  int t2 = z+t1;
  int t3 = x+4;
  int t4 = y*48;
  int t5 = t3 + t4; 
  int rval = t2*t5;
  return rval;
}

#4(%esp)存储储存着参数x,8(%esp)存储储存着参数y,12(%esp)存储储存着参数z

  movl    4(%esp), %ecx           #ecx = x
  movl    8(%esp), %edx           #edx = y
  leal    (%ecx,%edx), %eax       # eax = x + y       (t1)
  leal    (%edx,%edx,2), %edx     # edx = 3*y
  sall    $4, %edx                # edx = edx << 4    (t4)
  addl    12(%esp), %eax          # eax = z + t1      (t2)
  leal    4(%ecx,%edx), %edx      # edx = x+4 + t4    (t5)
  imull    %edx, %eax             # eax = t5 + t2     (ravl)

2.实例2

int logical(int x,int y){
  int t1 = x^y;
  int t2 = t1 >> 17;
  int mask = (1<<13) - 7;
  int rval = t2 & mask;
  return rval;
}

  movl    8(%esp), %eax   # 将Y的值赋值给eax
  xorl    4(%esp), %eax   # x与Y进行异或运算，结果赋值给eax
  sarl    $17, %eax       # 给t1进行17位的算数右移，结果赋值给eax
 andl    $8185, %eax     # 8185是1左移13位减去7的结果，在编译之前就计算得出的