Get a specific bit from byte

Question

I have a byte  specifically one byte from a byte array which came in via UDP sent from another device  This byte stores the on off state of 8 relays in the device   How do I get the value of a specific bit in said byte  Ideally an extension method would look the most elegant and returning a bool would make the most sense to me   public static bool GetBit this byte b  int bitNumber          black magic goes here

User · Answer

Flags  enum Relays   byte       relay0   1  lt  lt  0      relay1   1  lt  lt  1      relay2   1  lt  lt  2      relay3   1  lt  lt  3      relay4   1  lt  lt  4      relay5   1  lt  lt  5      relay6   1  lt  lt  6      relay7   1  lt  lt  7    public static bool GetRelay byte b  Relays relay        return  Relays b HasFlag relay

User · Answer

Easy  Use a bitwise AND to compare your number with the value 2 bitNumber  which can be cheaply calculated by bit-shifting     your black magic var bit    b  amp   1  lt  lt  bitNumber-1      0    EDIT  To add a little more detail because there are a lot of similar answers with no explanation   A bitwise AND compares each number  bit-by-bit  using an AND join to produce a number that is the combination of bits where both the first bit and second bit in that place were set  Here s the logic matrix of AND logic in a  nibble  that shows the operation of a bitwise AND     0101  amp  0011   ----   0001   Only the last bit is set  because only the last bit of both summands were set   In your case  we compare the number you passed with a number that has only the bit you want to look for set  Let s say you re looking for the fourth bit     11010010  amp  00001000   --------   00000000      0  so the bit is not set    11011010  amp  00001000   --------   00001000      0  so the bit is set   Bit-shifting  to produce the number we want to compare against  is exactly what it sounds like  take the number  represented as a set of bits  and shift those bits left or right by a certain number of places  Because these are binary numbers and so each bit is one greater power-of-two than the one to its right  bit-shifting to the left is equivalent to doubling the number once for each place that is shifted  equivalent to multiplying the number by 2 x  In your example  looking for the fourth bit  we perform          1  2 0   lt  lt   4-1            8  2 3  00000001        lt  lt   4-1     00001000   Now you know how it s done  what s going on at the low level  and why it works

User · Answer

try this   return  b  amp   1  lt  lt  bitNumber   gt 0

User · Answer

This is works faster than 0 1 milliseconds    return  b  gt  gt  bitNumber   amp  1

User · Answer

This  public static bool GetBit this byte b  int bitNumber       return  b  amp   1  lt  lt  bitNumber      0      should do it  I think

User · Answer

The method is to use another byte along with a bitwise AND to mask out the target bit   I used convention from my classes here where  0  is the most significant bit and  7  is the least   public static class ByteExtensions          Assume 0 is the MSB andd 7 is the LSB      public static bool GetBit this byte byt  int index                if  index  lt  0    index  gt  7              throw new ArgumentOutOfRangeException             int shift   7 - index              Get a single bit in the proper position          byte bitMask    byte  1  lt  lt  shift               Mask out the appropriate bit          byte masked    byte  byt  amp  bitMask               If masked    0  then the masked out bit is 1             Otherwise  masked will be 0          return masked    0

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Try the code below  The difference with other posts is that you can set get multiple bits using a mask  field   The mask for the 4th bit can be 1 lt  lt 3  or 0x10  for example       public int SetBits this int target  int field  bool value                if  value    set value                       return target   field                    else   clear value                       return target  amp    field                        public bool GetBits this int target  int field                return  target  amp  field   gt  0             Example             bool is ok   0x01AF GetBits 0x10     false         int res   0x01AF SetBits 0x10  true           is ok   res GetBits 0x10       true

User · Answer

another way of doing it     return   b  gt  gt  bitNumber   amp  1     0

User · Answer

Using BitArray class and making an extension method as OP suggests   public static bool GetBit this byte b  int bitNumber        System Collections BitArray ba   new BitArray new byte   b        return ba Get bitNumber

User · Answer

While it s good to read and understand Josh s answer  you ll probably be happier using the class Microsoft provided for this purpose  System Collections BitArray  It s available in all versions of  NET Framework

[c#] Get a specific bit from byte

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