Determine length of bitstring

Question

Optimize the following function for number of tokens:

int length(int x)
{
    switch (x)
    {
    case 1: return 1;
    case 3: return 2;
    case 7: return 3;
    case 15: return 4;
    case 31: return 5;
    case 63: return 6;
    case 127: return 7;
    case 255: return 8;
    case 511: return 9;
    case 1023: return 10;
    case 2047: return 11;
    default: return 0;
    }
}

No additional cases besides the 11 shown above need to be handled. The default case will never occur (but Java needs one, or else it does not compile). Any programming language is allowed. Whole programs are also allowed.

If you embed another language inside strings, the tokens in the embedded language count as well.

The baseline is 53 tokens, since separators don't seem to count in atomic-code-golf. Have fun!

Answer 1

Pyth, 4 tokens

slhQ

Exact same algorithm as my CJam solution.

Tokens:

s            int(
 l               log2(
  h                   1 +
   Q                  eval(raw_input()) ))

Try it online here

Answer 2

gcc, 4 tokens

# define length __builtin_popcount

Answer 3

J, 3 tokens

#@:#:

• #:: binary array (5 -> 1 0 1)
• @:: Atop: (f@:g x -> f(g(x)))
• #: Lenght (# 1 0 1 -> 3)

Answer 4

CJam, 5 tokens

This is a simple equation, where y = log₂(x + 1)

ri)2mL

Tokens:

r           e# Read input token as string
 i          e# Convert to integer
  )         e# Increment it by 1
   2        e# This serves as the base of the log
    mL      e# Log the first number in the base of the second number. i.e. ri) log 2

Try it here

Answer 5

Java, 5 tokens

x -> +" \1 \2   \3       \4               \5                               \6                                                               \7                                                                                                                               \10                                                                                                                                                                                                                                                               \11                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               \12                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               \13".charAt(x)

1. x
2. +
3. string
4. charAt
5. x

Answer 6

Python 2, 7 tokens

This function passes the tests, but is not a reliable substitute for log2.

lambda x: len(bin(x))-2

Answer 7

Clip 10, 4 tokens

lb2n

Explanation

   n  .- the numeric value of the input -.
 b2   .- convert to binary              -.
l     .- length; i.e., number of digits -.