# fact3.mips
# Given a number n in $1, calculate n!.
# Return the result in $1.
# No other registers are modified.
#
# Register Usage:
# $1 - Accumulates result
# $2 - Counter of current value to multiply

.globl fact3

fact3:  addi $30, $30, -4
        sw $2, 0($30)

        add $2, $1, $0     # Copy n to $2
        addi $1, $0, 1     # Initialize result to 1
        beq $0, $2, done   # If none left, finish
loop:   mult $1, $2        # Multiply result by counter
        mflo $1            # Get product from Lo register
        addi $2, $2, -1    # Decrement counter
        bne $0, $2, loop   # If more to do, loop

done:   lw $2, 0($30)
        addi $30, $30, 4
        jr $31             # Return to caller