Left shift Float type

Question

get a complier error while trying to do

float_val=float_val<<1;

It gives out a error saying "error C2296: '<<' : illegal, left operand has type 'float '"

Can't v left shift float vars? Why is this so?

Answer 1

Shifting floats makes no sense since it's represented as the concatenation of a sign bit, an exponent and a mantissa. Since shifting operation is about shifting bits, it would imply shifting bits from mantissa to exponent and / or to sign bit.

Answer 2

Floating point numbers don't have bits at the level of value-representation, which is why you can't apply bitwise operations to them.

See this answer for more information.

Answer 3

You'd have to transform the float to something else first. Such as:

float f = 128;
f = (float) (((int) f) << 1 );

And in the above, f should be 256.0.

Now obviously this is problematic if you start with 128.4 as the cast will drop the .4. You may not want to be using a float in first place.

Answer 4

Since the left shift operator is defined as multiplication by a power of 2, it makes perfect sense for floating point types. However, the C language does not define its use, so instead you have to use the scalbn function or similar.

Answer 5

You cannot left shift objects of float type.

C says the operands of the bitwise shift operators shall have integer type.

Answer 6

Check out the standard function ldexpf if you want to quickly multiply or divide a float by a power of 2. A bit obscure obviously :-).

https://linux.die.net/man/3/ldexpf