Extract unsigned values from certain bits in C# ushort

[Johan Simpson]

Hi all.

I need a good way of extracting values from certain bits inside a unsigned short:


The definition of the 4 alarms inside the ushort:

Name......Range .......Bits
Alarm4....0-15....13/16-16/16
Alarm3....0-15....9/16-12/16
Alarm2....0-15....5/16-8/16
Alarm1....0-15....1/16-4/16


The value of the ushort: 4383 or (1000100011111 in binary)


So what i want to achieve is:
100110011001100 1
Alarm1.....Alar m2.....Alarm3.. ....Alarm4
1001.......1001 .......1001.... ....1001

Gets translated into:
Alarm1....Alarm 2....Alarm3.... Alarm4
9............9. ...........9... .........9


Using the pseudo code:

 getValueFunc(ushort bits, int offset);

 ushort u = 4383;
 UInt16 Alarm1Value = getValueFunc(u, 1);
 UInt16 Alarm2Value = getValueFunc(u, 5);
 UInt16 Alarm3Value = getValueFunc(u, 9);
 UInt16 Alarm4Value = getValueFunc(u, 13);

Thank you very much in advance for your time.

Regards,
Johan

[Christian Binder]

Taking the second four bits:
1001100110011001 if you & (and) it with
000000001111000 0 you'll get
000000001001000 0 when you shift this thing by four places,
000000000000100 1 you'll get what you want

this would look like

ushort getValueFunc(ushort bits, int offset) {
  //assume offset starts by zero (right four bytes)
  //bits:   1001 1001 1001 1001
  //offset:  3    2    1    0
  //result:  9    9    9    9

  ushort and_value = 15; // 1111
  and_value <<= offset * 4;
    //move it offset*4 binary places to the left
    //offset  and_value
        0                   1111
        1               11110000
        2           111100000000
        3       1111000000000000


  bits &= and_value; //and-ing

  bits >>= offset * 4:
  //move it back offset*4 binary places to the right

  return bits;
}

I hope this works and helps :-)

[Johan Simpson]

Just tested it, works 100%.

Thank you very much for the solution and explaination, now it makes sense for people like me with little binary experience :)

[Christian Binder]

Fine :-) you're welcome