please wait
Bitwise operators
Nov 28, 2012 at 6:05pm
hello
i want to check if the last two bits of a number a are 1. am i going to do
i want to check if the last two bits of a number a are 1. am i going to do
if(a&3==3)? (because in binary 3 is written as 11)
Nov 28, 2012 at 6:15pm
That looks correct.
One way of looking at the bitwise & operator, is a method of setting bits off.
So we take the binary value 00000011, then take the result of that & your variable, all the bits where you used a 0 will be set off in the result, and the bits where you had a 1 will retain the original value.
So the result of (a & 3) will have a zero in every position except the last two bits. You test if that == 3 to confirm that both bits are a 1.
One way of looking at the bitwise & operator, is a method of setting bits off.
So we take the binary value 00000011, then take the result of that & your variable, all the bits where you used a 0 will be set off in the result, and the bits where you had a 1 will retain the original value.
So the result of (a & 3) will have a zero in every position except the last two bits. You test if that == 3 to confirm that both bits are a 1.
Nov 28, 2012 at 9:10pm
Another possibilities is using the expression
if ( a % 4 == 3 )
if ( a % 4 == 3 )
Dec 1, 2012 at 11:53am
Hey guys I have a question.
I don't know the bit sort rule of negative and float-double value. And why I can't perform (2.4 % 5) - modulus a float-double value or execute any bitwise operator command?
I don't know the bit sort rule of negative and float-double value. And why I can't perform (2.4 % 5) - modulus a float-double value or execute any bitwise operator command?
Dec 1, 2012 at 12:00pm
Because those operations apply only to integers.
If you want to use such operations assign your value to an integer variable, or cast it to an integer type.
If you want to use such operations assign your value to an integer variable, or cast it to an integer type.
Dec 1, 2012 at 12:07pm
But, why? And why...C++ doesn't support unsigned float, short float, and long long int???
Dec 1, 2012 at 12:18pm
C++11 has long long int.
I don't think unsigned float would be as useful as unsigned integers, and there are not much hardware support for it.
You already have float, double and long double so we don't need yet another type. If C++ added a short float it would probably be the same size as float on most implementations because making it smaller would just slow things down because there is no hardware support for such 2 byte floats.
I don't think unsigned float would be as useful as unsigned integers, and there are not much hardware support for it.
You already have float, double and long double so we don't need yet another type. If C++ added a short float it would probably be the same size as float on most implementations because making it smaller would just slow things down because there is no hardware support for such 2 byte floats.
Dec 1, 2012 at 1:18pm| Jackson Marie wrote: |
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| But, why? |
The internal representation of floating point numbers is optimised to match the hardware. The number will probably have separate sign, mantissa and exponent. Attempting a direct bitwise operation wouldn't make sense, as the three separate parts could be mixed up.
The point about using various bitwise operations on integer values is that the hardware and machine language is able to directly perform the operation, making it very fast and efficient. There are no such hardware equivalents for floating point values.
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