Do you have any simple ways to make a value in a register in MIPS as an absolute value?
Here is a pretty simple way to do it.
#assume you want the absolute value of r1
ori $2, $zero, $1 #copy r1 into r2
slt $3, $1, $zero #is value < 0 ?
beq $3, $zero, foobar #if r1 is positive, skip next inst
sub $2, $zero, $1 #r2 = 0 - r1
foobar:
#r2 now contains the absolute value of r1