MIPS（组合件）-如何对浮点数取整？

Question

Let's say I have a float number 123.4567... in $f0 register.

How can I round that to 123,46 and store it to $f1 register?

I need a solution that also works with negative numbers:

-123.4567... --> -123.46

edit. And also with integers:

-4.0 --> -4.0

Answer 1

Pseudo code:

Multiply by 100.0
If sign is positive
  Add 0.5
Else
  Subtract 0.5
Convert to integer
Convert back to float
Divide by 100.0

Answer 2

Building off of @PaulR's suggestion, you can either add +0.5 or -0.5 if it's positive or negative respectively.

This can either be accomplished with a branch (for clarity):

Multiply by 100.0
if num >= 0
    Add 0.5
else
    Add -0.5
Convert to integer
Convert back to float
Divide by 100.0

Or if performance is important, by masking the sign bit to get a 0.5 that's positive or negative depending on the sign of your input:

Multiply by 100.0
$f2 = $f0 & (0x80000000 | 0.5))
$f0 += $f2
Convert to integer
Convert back to float
Divide by 100.0