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 snippets
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Counting (c) bits set in x for (c = 0; x; c++) { x &= vx- 1; }
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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 arithmetics
x = y << n
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Multiply by n times 2 |
x = y >> n
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Divide by n times 2 |
return (x & 1) == 0
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Is x even? |
return (x && !(x & (x - 1)))
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Is x power of 2? |
return (x ^ y) < 0
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Has x opposite sign than y? |
y ^ ((x ^ y) & -(x < y))
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min(x,y) |
x ^ ((x ^ y) & -(x < y))
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max(x,y) |
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Single bit operations
y = x | (1<<n)
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Set the nth bit |
y = x & ~(1<<n)
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Unset the nth bit |
y = x ^ (1<<n)
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Toggle the nth bit |
return x & (1<<n)
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Test if the nth bit is set |
y = x & (x-1)
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Turn off rightmost 1bit |
y = x & (-x)
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Isolate rightmost 1bit |
y = x | (x-1)
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Right propagate rightmost 1bit (fill in ones) |
y = x | (x+1)
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Turn on rightmost 0bit |
y = ~x & (x+1)
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Isolate rightmost 0bit |
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