rol pseudo-instruction MIPS code

Question

The instructions is:

rol $t0, $t1, n
rolv $t0, $t1, $t2

n: 1bit- 31bit

Is this correct translation of the above instructions?

srl $t1, $s1, 1
sll $t2, $s1, 31
or $s2, $t1, $t2 #combine_words

Answer 1

For rol $t0, $t1, n I would use $at as the scratch register.

Suppose you want to rotate 4 binary digits to the left:

   srl $at, $t1, 28  # 32-4 = 28
   sll $t0, $t1, 4
   or $t0, $t0, $at

For rolv $t0, $t1, $t2 I would emit ($t2 holds the number of bits to rotate):

   sllv $t0, $t1, $t2
   subu $at, $zero, $t2
   addiu $at, $at, 32    # $at = 32-$t2
   srlv $at, $t1, $at
   or $t0, $t0, $at