输出浮点值

Question

我只是想创建一个程序，从键盘上读取浮点值(即单精度数字(，然后输出它，没有警告或错误，但我无法得到正确的答案，相反，我得到了0.00000000。我的代码出了什么问题？这是我的代码：

.data 0x10000000
msg1: .asciiz "Please enter a float: "
.text
.globl main
main: addu $s0, $ra, $0  # save $31 in $16
li $v0, 4 # system call for print_str
la $a0, msg1 # address of string to print
syscall
li $v0, 6 # system call for read_float
syscall # the float placed in $f0
mtc1 $t0, $f0# move the number in $t0
sll $t0, $t0, 4 
# print the result
li $v0, 2 # system call for print_float
mfc1 $t0, $f12 # move number to print in $f12
syscall
# restore now the return address in $ra and return from main
addu $ra, $0, $s0 # return address back in $31
jr $ra # return from main

Answer 1

您的mtc1和mfc1是向后的。

• mtc1表示GPR -> FPR
• mfc1表示GPR <- FPR

所以，如果我们看看这个代码的实际作用：

mtc1 $t0, $f0      # Sets $f0 = $t0. You haven't specified a value for $t0 at this point,
# but it doesn't really matter since you're not using $f0 any more
# after this point.
sll $t0, $t0, 4    # Shifts whatever was in $t0 4 bits to the left.
li $v0, 2          # System call for print_float.
mfc1 $t0, $f12     # Set $t0 = $f12.
syscall            # Calls print_float without having specified a value for $f12.

我不明白这个转变的意义，因为你说你只想打印读取的数字，所以上面的代码可以替换为：

mov.s $f12, $f0
li $v0, 2
syscall

如果您do出于某种原因仍想执行该转换，则需要将mtc1更改为mfc1，反之亦然。