A mask defines which bits you want to keep, and which bits you want to clear. Masking is the act of applying a mask to a value. This is accomplished by doing: Bitwise ANDing in order to extract a subset of the bits in the value Bitwise ORing in order to set a subset of … Read more
Very interesting question, and clever trick. Let’s look at a simple example of getting a single byte manipulated. Using unsigned 8 bit for simplicity. Imagine your number is xxaxxbxx and you want ab000000. The solution consisted of two steps: a bit masking, followed by multiplication. The bit mask is a simple AND operation that turns … Read more
Two’s complement is a clever way of storing integers so that common math problems are very simple to implement. To understand, you have to think of the numbers in binary. It basically says, for zero, use all 0’s. for positive integers, start counting up, with a maximum of 2(number of bits – 1)-1. for negative … Read more
This is known as the ‘Hamming Weight’, ‘popcount’ or ‘sideways addition’. Some CPUs have a single built-in instruction to do it and others have parallel instructions which act on bit vectors. Instructions like x86’s popcnt (on CPUs where it’s supported) will almost certainly be fastest for a single integer. Some other architectures may have a … Read more
The bit shifting operators do exactly what their name implies. They shift bits. Here’s a brief (or not-so-brief) introduction to the different shift operators. The Operators >> is the arithmetic (or signed) right shift operator. >>> is the logical (or unsigned) right shift operator. << is the left shift operator, and meets the needs of … Read more
Setting a bit Use the bitwise OR operator (|) to set a bit. number |= 1UL << n; That will set the nth bit of number. n should be zero, if you want to set the 1st bit and so on upto n-1, if you want to set the nth bit. Use 1ULL if number … Read more