Shift Left One Bit
Purpose:
To shift the contents of the 16-bit variable value at location 6000 to the left one bit. The result is to be stored back into the the variable value.
Sample Test Data:
input: value: (6000) = 57B616 = 0101 0111 1011 01102
output result: (6000) = AF6C16 = 1010 1111 0110 11002
Note that (6000) means "the contents of location with
address 6000". Clearly what we mean here is that the
contents of
6000 and 6001 taken together is 57B6, where (6000) = 57 and
(6001) = B6
Source Code:
| data | equ | $6000 | |
| program | equ | $4000 | |
| org | data | ||
| value | ds.w | 1 | ;value to be shifted left |
| org | program | ||
| move.w | value, d0 | ;get value to be shifted | |
| lsl.w | #1, d0 | ;shift left one bit | |
| move.w | d0, value | ;store shifted result |
Shifting a number left one digit always causes the number to be multiplied by the base of the number system, in this case 2. It may be less time consuming to multiply a number by 2 this way than to use the MUL instruction.