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Binomial: Faster sampling for n * p < 10 #735

Merged
merged 3 commits into from Feb 27, 2019
Merged

Binomial: Faster sampling for n * p < 10 #735

merged 3 commits into from Feb 27, 2019

Commits on Feb 26, 2019

  1. Binomial: Faster sampling for n * p < 10 

    Fixes rust-random#734.
    @vks
    vks committed Feb 26, 2019
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  2. Binomial: Add benchmark for small n * p 

    Our previous implementation was very slow (rust-random#734). The benchmarks makes
sure we won't have such regressions in the future.
    @vks
    vks committed Feb 26, 2019
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  3. Binomial: Use integer exponentation 

    This increase performance significantly, see below. However, it requires
shipping our own integer exponentiation implementation, because `u64`
exponents are not supported by `std` or `num`.

Before:
```
test distr_binomial       ... bench:  88,365 ns/iter (+/- 2,215) =90 MB/s
test distr_binomial_small ... bench:  33,775 ns/iter (+/- 5,494) =236 MB/s
test misc_binomial_1      ... bench:      13 ns/iter (+/- 2)
test misc_binomial_10     ... bench:      72 ns/iter (+/- 1)
test misc_binomial_100    ... bench:      71 ns/iter (+/- 11)
test misc_binomial_1000   ... bench:     624 ns/iter (+/- 19)
test misc_binomial_1e12   ... bench:     681 ns/iter (+/- 18)
```

After:
```
test distr_binomial       ... bench:  44,354 ns/iter (+/- 3,518) = 180 MB/s
test distr_binomial_small ... bench:  22,736 ns/iter (+/- 514) = 351 MB/s
test misc_binomial_1      ... bench:      10 ns/iter (+/- 0)
test misc_binomial_10     ... bench:      23 ns/iter (+/- 0)
test misc_binomial_100    ... bench:      27 ns/iter (+/- 4)
test misc_binomial_1000   ... bench:     621 ns/iter (+/- 15)
test misc_binomial_1e12   ... bench:     686 ns/iter (+/- 20)
```
    @vks
    vks committed Feb 26, 2019
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