NEGU - MIPS instruction reference

neguNegate unsigned (no overflow trap) Pseudo-instruction
Sets $t1 to the negation of $t2, wrapping on overflow instead of trapping.
Forms  negu ,   
Operands $t1 Any general-purpose register, $0 to $31, using its numeric or named spelling, such as $8 or $t0 ($zero is $0; $ra is $31). 
$t2 A general-purpose register. It may be the same register as $t1. 
 # Negate 7 without overflow trapping. Inspect $t2: 0xFFFFFFF9.
li $t0, 7
negu $t2, $t0