4 ms·

Lookup table seems silly when you can take advantage of the floating point format. In C, I think you can more or less just do something like: uint64_t e =

• sitkack 11y ago
  That doesn't look like valid Scala code.
  • waxjar 11y ago
    > In C
    • draw_down 11y ago
      So, not valid Scala then.
• wiml 11y ago
  In C you can use scalbn(), which a good compiler would hopefully optimize to something equivalent to what you wrote. Java has scalb(), presumably based on the C function.
  • cozzyd 11y ago
    It doesn't look like gcc (4.8.3) inlines scalbn on -O3 (unless I need another flag...). I see callq(scalbn) in the disassembly.
  • stephencanon 11y ago
    That's not a legal optimization as it gets all sorts of edge cases wrong. For example scalbn(0, anything) is zero, whereas simply adding to the exponent will produce some arbitrary power of two or infinity.
• brianwawok 11y ago
  Scala has bitewise operators http://www.tutorialspoint.com/scala/scala_bitwise_operators.htm http://www.tutorialspoint.com/scala/scala_bitwise_operators.... So the "<<" is easy enough to cover. I do not know what the * is going, if it involves pointer something something then it may not be possible to replicate.
  • cozzyd 11y ago
    I'm just reinterpreting the 64-bit integer as a double-precision floating point number (there are other ways to do this in C, for example using a union).
    • shanemhansen 11y ago
      Java has a type called bytebuffer that might do the trick: http://docs.oracle.com/javase/7/docs/api/java/nio/ByteBuffer.html#getFloat() http://docs.oracle.com/javase/7/docs/api/java/nio/ByteBuffer... I don't know how that would get optimized by the jit at runtime though.
      • jdmichal 11y ago
        Don't be silly. These functions are built into `Float` and `Double`. http://docs.oracle.com/javase/7/docs/api/java/lang/Double.html#doubleToRawLongBits%28double%29 http://docs.oracle.com/javase/7/docs/api/java/lang/Double.ht... http://docs.oracle.com/javase/7/docs/api/java/lang/Double.html#longBitsToDouble%28long%29 http://docs.oracle.com/javase/7/docs/api/java/lang/Double.ht... Both are marked as native functions in OpenJDK 7: http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/7u40-b43/java/lang/Double.java#Double.doubleToRawLongBits%28double%29 http://grepcode.com/file/repository.grepcode.com/java/root/j... http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/7u40-b43/java/lang/Double.java#Double.longBitsToDouble%28long%29 http://grepcode.com/file/repository.grepcode.com/java/root/j...
• b0b0b0b 11y ago
  From the article, she says they tried "1.0 / (1 << mj)", which turned out to be slower than the lookup table. May or may not be equivalent to java.lang.Math.scalb, I dunno.