【发布时间】：2014-03-08 05:06:58
【问题描述】：
所以我正在处理一项在 MIPS 中对数组进行排序的任务。要排序的数据在单独的 .asm 文件中给出，如下所示：
.data
.word 3
.word 40
.word 30
.word 70
.text
我决定使用冒泡排序。我相当肯定我的算法是合理的，并且它似乎对数据进行了正确的排序。这个项目的有趣之处在于，我们排序的值将作为 MIDI 音符播放，作为测试程序的一种手段（因此，音符自然应该按升序播放）。当我测试我的代码时，这运行得很好，但是，我在 MIDI 音符的末尾听到了一些奇怪的节拍。我逐步检查了我的代码，发现最后，$t1（我用来与循环迭代器比较完整性的值）的值为 7，而我预计它的值为 3。我将 $t1 分配为 0($t2)，$t2 是 0x10010000，我假设它仍然是我的数组的基地址。数组的基地址应该是 3，不是吗？
我对为什么 $t1 是 7 有点困惑......有什么建议吗？我在下面包含了我的所有代码。
#ec2.asm
.include "ec2_data.asm" #must be in the same directory as ec2.asm
#ec2_data.asm: puts some values in the "data segment"
#the first value is the number of values to sort (n)
#the remaining n word values are the data to sort
#the values will be stored in memory as word values starting
# address 0x10010000
j main
#$t2 is hasChanged
#$t3 is itemCount
#$t4 is i, our iterator in the for loop
#$t5 is array[i] (temp)
#$t6 is array[i+1] (temp)
while_label:
beq $t2, $zero, done_sorting #checks to see if the previous iteration switched any values. If not, we are done.
addi $t2, $zero, 0 #initialize hasChanged to 0
addi $t3, $t3, -1 #decrement itemCount by -1
addi, $t0, $t0, 4 #add 4 to the array offset
addi, $t4, $zero, 0 #set our for loop iterator to 0
for_label:
lw $t5, 0($t0) #set a temp value equal to array[i]
lw $t6, 4($t0) #set a temp value equal to array[i+1]
beq $t4, $t3, while_label #for loop: if i = itemcount, we have incremented all the way through our for loop
bge $t6, $t5, skip_swap #if array[i+1] is greater than or equal to array[i], we don't need to swap these values
#swap
sw $t6, 0($t0) #set array[i] equal to array[i+1]
sw $t5, 4($t0) #set array[i+1] equal to the temp value
addi $t2, $t2, 1 #set hasChanged to 1 to indicate that a swap has been made
skip_swap:
addi, $t4, $t4, 1 #increment i by 1 (for loop iterator)
j for_label #keep the for loop going!
main:
#read values
addi $t0, $zero, 0x10010000 #sets $t0 to be the base address of the array
addi $t2, $zero, 1
lw $t3, 0($t0) #stores n in $t3
j while_label
done_sorting:
# adapted from MIDI example
#duration 25 ms
#instrument (whichever)
#volume 64
addi $v0, $zero, 33 # midi out synchronous
addi $t2, $zero, 0x10010000 # address of original array (which should by now be sorted)
addi $a1, $zero, 250 # duration (ms)
addi $a2, $zero, 1 # instrument
addi $a3, $zero, 64 # volume
addi $t0, $zero, 0 # counter
lw $t1, 0($t2) # end of the loop (should be n)
addi $t1, $t1, 4 # adds four to the array offset in $t1
lw $a0, 0($t2) # stores the first sorted value ( 4($t1) ) in $a0
midi_loop:
beq $t0, $t1, done
addi $t2, $t2, 4
lw $a0, 0($t2)
syscall
addi $t0, $t0, 1
j midi_loop
done:
#addi $v0, $zero, 10 # syscall for exit
#syscall # clean exit
【问题讨论】：