I think your example would be a lot more readable if you expressed the constants in binary or hex.

If each result is approximately equally likely, I think it would be more efficient to do a binary chop: a 64-bit input should take no more than 6 tests. For accuracy you should probably write some code to generate this:

  my $m =
    $z > 0x00000000ffffffff
      ? $z > 0x0000ffffffffffff
        ? $z > 0x00ffffffffffffff
          ? $z > 0x0fffffffffffffff
            ? $z > 0x3fffffffffffffff
              ? $z > 0x7fffffffffffffff ? 0x8000000000000000 : 0x40000
+00000000000
              : $z > 0x1fffffffffffffff ? 0x2000000000000000 : 0x10000
+00000000000
... etc.

[download]

I don't know much about Bloom filters, but it's possible you could construct one to do it faster. Another possibility would be some XS (or Inline C) - some processors have a single instruction to return this, and C compilers often provide functions that use such instructions where available, and fall back to an alternative implementation otherwise. In this case I think you could do it using __builtin_clz() if using gcc.

In reply to Re: Most Significant Set Bit by hv
in thread Most Significant Set Bit by coldr3ality

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