Question: does whitespace detection by bitwise operation make jsoniter-scala faster?

[i10416]

There is a technique to detect whitespace using bitwise operation.

val spaces = 1L<<' ' | 1L<<'\n' | 1L<<'\r' | 1L<<'\t'
// because ' ', '\n', '\r', '\t' are less than or equals to 32, 
// you can get bit flags for whitespaces shifting 1 by their int value.

if (1<<char&spaces != 0) {
  // char is whitespace here
}

The same idea is discussed in typelevel/jawn#26 (comment)

Does this technique make jsoniter-scala faster or jsoniter-scala has already adopted this technique?

[plokhotnyuk]

Currently it is checked by the following code:

b == ' ' || b == '\n' || (b | 0x4) == '\r'

Predicted condition jumps are quite cheep and can have throughput of 2 checks per cycle on contemporary CPUs.

We could try it in the JVM version of JsonReader:

b <= 32 && ((1L << b) & 0x100002600L) == 0

Clang is able to make branch-less object code from that: