Question

int strlen( char* string ) {
    int count = 0;
    while( *string != ‘\0’ ) {
        string++;
        count++;
    }
    return count;
}

我正在研究这些......
我想知道你是否可以提出任何优化建议？以下是MIP代码......

strlen:
li $t0, 0 # initialize the count to zero
loop:
lbu $t1, 0($a0) # load the next character into t1
beqz $t1, exit # check for the null character
addi $a0, $a0, 1 # increment the string pointer
addi $t0, $t0, 1 # increment the count
j loop # return to the top of the loop
exit:

Answer 1

 // will (probably) output x86_64 assembly (or your computer's native assembly)
 gcc -Wall -S test.c


 // will output mips3 assembly
 gcc -Wall -march=mips3 -S test.c

或者通过优化：

 // will output (optimized) mips3 assembly (if possible)
 gcc -Wall -O3 -march=mips3 -S test.c

Answer 2

好吧，你可以优化C，虽然在优化器中弄清楚你被允许这样做可能很棘手。将您的代码与：

进行比较

int strlen( char* string ) {
    char *sp = string;
    while( *sp != ‘\0’ ) sp++;
    return sp - string;
}

这应该意味着主循环只包含一个addi语句而不是2。

Answer 3

不知道MIPS，但你可以删除一些命令：

strlen:
li $t0, $a0     # init ptr
loop:
lbu $t1, 0($t0) # load the next character into t1
beqz $t1, exit # check for the null character
addi $t0, $t0, 1 # increment the string pointer
j loop # return to the top of the loop
exit:
sub $v0, $t0, $a0

有没有办法进一步优化这个MIPs代码？

3 个答案: