Cheatography
https://cheatography.com
When dealing with software close to hardware, these bit hacks might come in handy. From setting and getting to parity and calculations.
This is a draft cheat sheet. It is a work in progress and is not finished yet.
C/C++ bitwise operations& | AND | | | OR | ^ | XOR | ~ | NOT | << | SHIFT (left) | >> | SHIFT (right) |
Useful snippetsCounting (c) bits set in x for (c = 0; x; c++) { x &= vx- 1; }
| Computing parity in parallel (32 Bit) x ^= x >> 16; x ^= x >> 8; x ^= x >> 4; x &= 0xf; return (0x6996 >> x) & 1;
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| | Integer arithmeticsx = y << n
| Multiply by n times 2 | x = y >> n
| Divide by n times 2 | return (x & 1) == 0
| Is x even? | return (x && !(x & (x - 1)))
| Is x power of 2? | return (x ^ y) < 0
| Has x opposite sign than y? | y ^ ((x ^ y) & -(x < y))
| min(x,y) | x ^ ((x ^ y) & -(x < y))
| max(x,y) |
| | Single bit operationsy = x | (1<<n)
| Set the nth bit | y = x & ~(1<<n)
| Unset the nth bit | y = x ^ (1<<n)
| Toggle the nth bit | return x & (1<<n)
| Test if the nth bit is set | y = x & (x-1)
| Turn off rightmost 1bit | y = x & (-x)
| Isolate rightmost 1bit | y = x | (x-1)
| Right propagate rightmost 1bit (fill in ones) | y = x | (x+1)
| Turn on rightmost 0bit | y = ~x & (x+1)
| Isolate rightmost 0bit |
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