# fact1.mips
# Read a number n from standard input, then print n!
# (n factorial) on standard output.
#
# Register Usage:
# $1 - Accumulates result
# $2 - Counter of current value to multiply
# $4 - Used for output

.globl main

main:   trap 5           # Get integer into $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:   add $4, $0, $1   # Copy result into $4
        trap 1           # Print result (in $4)

        addi $4, $0, 10
        trap 101         # Print newline character

        trap 10          # Quit program