Algorithm to generate bit mask

by

One thing to notice about bitmasks like that is that they are always one less than a power of two.

The expression 1 << n is the easiest way to get the n-th power of two.

You don’t want Zero to provide a bitmask of 00000001, you want it to provide zero. So you need to subtract one.

mask = (1 << param) - 1;

Edit:

If you want a special case for param > 32:

int sizeInBits = sizeof(mask) * BITS_PER_BYTE; // BITS_PER_BYTE = 8;
mask = (param >= sizeInBits ? -1 : (1 <<  param) - 1);

This method should work for 16, 32, or 64 bit integers, but you may have to explicitly type the ‘1’.

More Related Contents:

  1. What is the fastest/most efficient way to find the highest set bit (msb) in an integer in C?
  2. Efficient Algorithm for Bit Reversal (from MSB->LSB to LSB->MSB) in C
  3. Explain this snippet which finds the maximum of two integers without using if-else or any other comparison operator?
  4. Algorithm to find the smallest number in an array in C [closed]
  5. Finding target sum of two numbers in array
  6. How can I multiply and divide using only bit shifting and adding?
  7. hash function for string
  8. Algorithm: efficient way to remove duplicate integers from an array
  9. What is CHAR_BIT?
  10. What is the efficient way to count set bits at a position or lower?
  11. How do you print the EXACT value of a floating point number?
  12. How to add two numbers without using ++ or + or another arithmetic operator
  13. Casting float to int (bitwise) in C
  14. What does the statement if (counter & (1
  15. Time complexity of a recursive algorithm
  16. How to find largest triangle in convex hull aside from brute force search
  17. Compute fast log base 2 ceiling
  18. Finding consecutive bit string of 1 or 0
  19. Why prefer start + (end – start) / 2 over (start + end) / 2 when calculating the middle of an array?
  20. warning: left shift count >= width of type
  21. Unexpected C/C++ bitwise shift operators outcome
  22. Rolling median algorithm in C
  23. Encoding int value as an IEEE-754 float (binary32)
  24. C reverse bits in unsigned integer
  25. Finding out the duplicate element in an array
  26. How to replace bits in a bitfield without affecting other bits using C
  27. Does C have any tools for doing string addition?
  28. Order of fields when using a bit field in C
  29. Algorithm to pick values from array that sum closest to a target value?
  30. Avoid Overflow when Calculating π by Evaluating a Series Using 16-bit Arithmetic?

Leave a Comment