# Operands
WORD_174
WORD_186

# Multiplication routine
# Restrictions:
#   Positive numbers only (31 shifts max since operands are twos-complement)
#   No overflow checking

multiply
    WORD_2147483648     # For use in setting sign for left shifts.
    IM_0                # For magnitude of left/right shifts.
    LDSP+0              # Sets up stack location to build/store result.
                        #-----
testbit                 #
    LDSP+3              #
    LDSP+2              #
    SHIFT               # Check Nth bit of second operand.
    IM_1                #
    AND                 #
    TEST                #
                        #-----
    BRZ>skipadd         #
    LDSP+4              #
    LDSP+3              #
    LDSP+3              #
    OR                  # Shift and add first operand to result if indicated.
    SHIFT               #
    ADD                 #
skipadd                 #
                        #-----
    LDSP+1              #
    IM_1                # Increment counter for shift magnitude
    ADD                 #
    STSP+1              #
                        #-----
    IM_30               #
    NOT                 #
    IM_1                #
    ADD                 # Test for completion of multiplication subroutine (31 shifts).
    LDSP+2              #
    ADD                 #
    TEST                #
    BRZ>cleanup         # If finished, cleanup and return from subroutine with result on TOS.
                        #-----
    IM_0                #
    TEST                # If not finished, repeat this process on the next bit.
    BRZ>testbit         #
                        #-----
cleanup                 #
    STSP+0              #
    STSP+0              #
    STSP+0              # Remove all subroutine temporaries from stack and return result on TOS.
    STSP+0              #
    HALT                #