Minor Description
Benchmark the speed of methods for producing a double from a long:
long v; double d1 = Double.longBitsToDouble(0x3FFL << 52 | v >>> 12) - 1.0; double d2 = (v >>> 12) * 0x1.0p-52d; // 1.0 / (1L << 52); double d3 = (v >>> 11) * 0x1.0p-53d; // 1.0 / (1L << 53);
Method d1 and d2 are both currently employed in the NumberFactory (makeDouble(int,int) and makeDouble(long)). However they suffer from producing a double whose least significant bit is always 0, i.e. they produce half of all possible double values from 0-1. This is discussed in the reference for the XorShiRo generators.
This task will benchmark the methods using JMH. A switch to method d3 may be appropriate as it generates more values. This is the method employed in JDK 1.7 ThreadLocalRandom.
A similar analysis can be made for producing a float:
int v; double f1 = Float.intBitsToFloat(0x7f << 23 | v >>> 9) - 1.0f; double f2 = (v >>> 9) * 0x1.0p-23f; // 1.0f / (1 << 23); double f3 = (v >>> 8) * 0x1.0p-24f; // 1.0f / (1 << 24)
Method f2 is currently used in the NumberFactory.
Attachments
Issue Links
- relates to
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RNG-81 NumberFactory to evenly sample all representable rationals between 0 and 1
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- Closed
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- links to
