Question

Create a MIPS program that takes an ASCII string of hexadecimal digits inputted by the user and converts it into an integer.

Answer 1

# $a0 - input, pointer to null-terminated hex string
# $v0 - output, integer form of binary string
# $t0 - address of start of lookup table
# $t1 - ascii value of the char pointed to
# $t2 - address of the integer value for the char in lookup table
# $t3 - integer value of hex char (0 - 15)

hex_convert:
li      $v0, 0                  # Reset accumulator to 0.
la      $t0, hexvals            # Load address of lookup into register.

loop:
lb      $t1, 0($a0)             # Load a character,
beq     $t1, $zero, end         # if it is null then return.
sll     $v0, $v0, 4             # Otherwise first shift accumulator by 4 to multiply by 16.
addi    $t2, $t1, -48           # Then find the offset of the char from '0'
sll     $t2, $t2, 2             # in bytes,
addu    $t2, $t2, $t0           # use it to calcute address in lookup,
lw      $t3, 0($t2)             # retrieve its integer value,
addu    $v0, $v0, $t3           # and add that to the accumulator.
addi    $a0, $a0, 1             # Finally, increment the pointer
j       loop                    # and loop.

end:
jr $ra

.data

IN PYTHON 3 , THE PROGRAM IS AS FOLLOWS ;-

def hexadecimalToDecimal(hexval):
    
    # Finding length
    length = len(hexval)
    
    # Initialize base value to 1,
    # i.e. 16*0
    base = 1
    dec_val = 0
    
    # Extracting characters as digits
    # from last character
    for i in range(length - 1, -1, -1):
        
        # If character lies in '0'-'9',
        # converting it to integral 0-9
        # by subtracting 48 from ASCII value
        if hexval[i] >= '0' and hexval[i] <= '9':
            dec_val += (ord(hexval[i]) - 48) * base
            
            # Incrementing base by power
            base = base * 16
        
        # If character lies in 'A'-'F',converting
        # it to integral 10-15 by subtracting 55
        # from ASCII value
        elif hexval[i] >= 'A' and hexval[i] <= 'F':
            dec_val += (ord(hexval[i]) - 55) * base
            
            # Incrementing base by power
            base = base * 16
            
    return dec_val

# Driver code
if __name__ == '__main__':
    
    hexnum = '1A'
    
    print(hexadecimalToDecimal(hexnum))

If the hexadecimal number is 1A.
dec_value = 1*(16^1) + 10*(16^0) = 26