cs61c_lab4

Exercise 1: Debugging megalistmanips.s

错误之处：

1. 偏移量没有乘4。
2. 偏移量应该加在结构体中数组的地址上而不是数组的地址的地址上。
3. 调用函数之前没有保存s1。
4. 在内存中取字应该是lw，而不是la。
5. 将s1中的内容移入a1，而不是将s1指向的地址中的内容移入a1。

代码如下：

mapLoop:
    # add t1, s0, x0      # load the address of the array of current node into t1
    lw t2, 4(s0)        # load the size of the node's array into t2

    # add t1, t1, t0      # offset the array address by the count
    # lw a0, 0(t0)        # load the value at that address into a0
    addi t1, x0, 4
    mul t1, t0, t1
    lw t3, 0(s0)
    add t1, t3, t1  
    lw a0, 0(t1)

    addi sp, sp, -4
    sw t1, 0(sp)

    jalr s1             # call the function on that value.

    lw t1, 0(sp)
    addi sp, sp, 4

    addi t1, x0, 4
    mul t1, t0, t1
    lw t3, 0(s0)
    add t1, t3, t1 
    sw a0, 0(t1)        # store the returned value back into the array

    addi t0, t0, 1      # increment the count
    bne t0, t2, mapLoop # repeat if we haven't reached the array size yet

    lw a0, 8(s0)        # load the address of the next node into a0
    mv a1, s1        # put the address of the function back into a1 to prepare for the recursion

    jal  map            # recurse
done:
    lw s0, 8(sp)
    lw s1, 4(sp)
    lw ra, 0(sp)
    addi sp, sp, 12
    jr ra

Exercise 2: Write a function without branches

代码如下：

f:
    addi a0, a0, 3
    addi t1, x0, 4
    mul a0, a0, t1
    add a0, a1, a0
    lw a0, 0(a0)
    jr ra          

或者：

f:
    addi a0, a0, 3
    slli a0, a0, 2
    add a0, a1, a0
    lw a0, 0(a0)
    jr ra