External module "math/base/special/fast/uint32-log2/docs/types/index.d"

Export assignment log2

• log2(x: number): number

• Computes an integer binary logarithm (base two).

  Method

  1. Note that the largest unsigned 32-bit integer is 4294967295, which is 2^{32}-1. Hence, the integer binary logarithm cannot exceed 31 (i.e., 16 + 8 + 4 + 2 + 1), which corresponds to the bit sequence

     00000000000000000000000000011111

  2. Initialize a return variable with the value zero.

  3. If at least one of the first sixteen most significant bits of the input 32-bit integer x is turned on, we know that the power to which the number 2 must be raised to obtain x is at least 16 (i.e., x > 65536). Hence, activate the corresponding bit of the return variable. Mutate x by shifting sixteen bits to the right, discarding the bits shifted off.

  4. Carry out the following steps with B in [ 8, 4, 2, 1 ]:

     • If at least one of the next B most significant bits of the current x is turned on, we know that the power to which the number 2 must be raised to obtain x has to be increased by B.
     • Activate the bit of the return variable that corresponds to B.
     • Mutate x by shifting B bits to the right, discarding the bits shifted off.

  5. The final value of the return variable is the integer binary logarithm of x.

  Parameters

  • x: number

    unsigned 32-bit integer

  Returns number

  integer binary logarithm

  Example

  var v = log2( 4 >>> 0 );
  // returns 2

  Example

  var v = log2( 8 >>> 0 );
  // returns 3

  Example

  var v = log2( 9 >>> 0 );
  // returns 3