I've got to write this program for C++

[RobDowneyJr]

What it says is:
For this lab, we will do multiplication of unsigned integers using integer additions, bitwise shifts, and bit testing.

1. If the multiplier bit is 1, put a copy of the multiplicand in the proper plce and add it to the product or
2. If the multiplier bit is 0, do nothing (add 0 to the product).

for (int i=1; i<=32; i++)

{
If the least significant bit of the multiplier is 1
add multiplicand to the product;
else do nothing;

shift the multiplicand left by 1 bit; //i.e. put it in proper place
shift the multiplier right 1 bit; //so we just need to test the least significant bit
}

your task in this lab is to implement the above algorithm in C++

the compiler reads regular decimal bits in binary i guess but how do i check to see if the least significant bit is 1 or 0?

 

[kleinesarschloch]

the expression (nVar & 0x01) will return true if the least significant bit in nVar is set.

 

[RobDowneyJr]

how do i get the binary bits to shift

 

[glugglug]

<< = shift left (x << y = x * 2^y)
>> = shift right (x >> y = x / 2^y)
Actually shift right is all you need, I think shift left is slower than addition on some CPUs and you never need to shift more than 1 bit at a time.

The algorithm you are looking for will be in any book on 6502 or similar era processor assembly -- those old CPUs didn't have multiplication and division operations built in so a subroutine to get that job done is pretty much a textbook problem.

Also, rather than always looping 32 times, the condition to break out of the loop can be that the number getting shifted right becomes 0. (This will make the loop a lot faster in what should be the more common cases).

 

[kleinesarschloch]

<< and >> operators... you should invest in a good c++ textbook.

 

[PrincessGuard]

int x;

x >> 4; //Shift 4 bits right
x << 3; //Shift 3 bits left

 

[RobDowneyJr]

is there an easy library function that lets you change from decimal to octal and hexadecimal?

 

[glugglug]

printf?.... or just some iomanip elements you pipe into your ostream (cout) ?