On Sun, 22 May 2022 20:19:38 GMT, Andrey Turbanov <aturba...@openjdk.org> wrote:
>> Repeatedly adding DoubleZigguratTables.exponentialX0 to extra causes a >> rounding error to accumulate at the tail of the distribution (probably >> starting around 2*exponentialX0 == 0x1.e46eff20739afp3 ~ 15.1); this fixes >> that by tracking the multiple of exponentialX0 as a long. (This changes the >> maximum possible output to `1.0p63 * DoubleZigguratTables.exponentialX0 == >> 0x1.e46eff20739afp65`; previously it would have been `0x1.0p56` because once >> `extra` reaches that amount, `x + extra == extra` due to the rounding error. >> This lowers the probability of reaching the maximum with an ideal PRNG from >> about `1.3877787807814488E-17` to about `1.4323726067488646E-20` (calculated >> using the identity `ln(x) == Math.log10(x)/Math.log10(Math.exp(1))`). > > src/java.base/share/classes/jdk/internal/util/random/RandomSupport.java line > 1411: > >> 1409: long U2 = (rng.nextLong() >>> 1); >> 1410: // Compute the actual x-coordinate of the randomly >> chosen point. >> 1411: x = Math.fma(X[j-1] - X[j], (double)U1, X[j] * >> 0x1.0p63)); > > Code is not compilable @Pr0methean As @turbanoff observes, I think there's a closing parentheses too much on L.1411 and one on L.1421. Which compiler are you using ;-) ? ------------- PR: https://git.openjdk.java.net/jdk/pull/8131
