better handling of the random value

[rok-cesnovar]

Submisison Checklist

• Run tests: ./runCmdStanTests.py src/test
• Declare copyright holder and open-source license: see below

Summary:

Fixes #803 with a more general solution. This PR modifies the arg_seed class by adding _random_value variable.

In case of using the default value of -1, value() would still return -1, while random_value would return the time dependant generated pseudo-random number. This circumvents the issue that we want the seed to be an unsigned int while also allowing -1 as a valid value.

The previous solution wrote the psedu-random number to directly to value which was a signed integer and that led to issues.

The alternative is to only use the non-negative values and stay with signed integer. But I dont think that was the intention when refactoring pseudo random generation awhile back.

Copyright and Licensing

Please list the copyright holder for the work you are submitting (this will be you or your assignee, such as a university or company): Rok Češnovar

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[stan-buildbot]

---

Name	Old Result	New Result	Ratio	Performance change( 1 - new / old )
gp_pois_regr/gp_pois_regr.stan	4.8	4.82	1.0	-0.43% slower
low_dim_corr_gauss/low_dim_corr_gauss.stan	0.02	0.02	0.94	-6.03% slower
eight_schools/eight_schools.stan	0.09	0.09	1.0	0.07% faster
gp_regr/gp_regr.stan	0.22	0.21	1.01	1.15% faster
irt_2pl/irt_2pl.stan	6.07	6.06	1.0	0.23% faster
performance.compilation	88.06	87.34	1.01	0.81% faster
low_dim_gauss_mix_collapse/low_dim_gauss_mix_collapse.stan	7.33	7.45	0.98	-1.6% slower
pkpd/one_comp_mm_elim_abs.stan	20.52	20.55	1.0	-0.12% slower
sir/sir.stan	88.95	96.66	0.92	-8.68% slower
gp_regr/gen_gp_data.stan	0.05	0.05	1.0	-0.4% slower
low_dim_gauss_mix/low_dim_gauss_mix.stan	2.98	2.96	1.01	0.58% faster
pkpd/sim_one_comp_mm_elim_abs.stan	0.31	0.31	0.99	-1.34% slower
arK/arK.stan	1.75	1.73	1.01	0.67% faster
arma/arma.stan	0.76	0.76	1.0	-0.19% slower
garch/garch.stan	0.63	0.63	1.0	-0.36% slower
Mean result: 0.990312530962

---

Jenkins Console Log
Blue Ocean
Commit hash: 091ae9c

---

Machine information

ProductName: Mac OS X ProductVersion: 10.11.6 BuildVersion: 15G22010

CPU:
Intel(R) Xeon(R) CPU E5-1680 v2 @ 3.00GHz

G++:
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix

Clang:
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix

[stan-buildbot]

---

Name	Old Result	New Result	Ratio	Performance change( 1 - new / old )
gp_pois_regr/gp_pois_regr.stan	4.86	4.85	1.0	0.24% faster
low_dim_corr_gauss/low_dim_corr_gauss.stan	0.02	0.02	0.96	-4.0% slower
eight_schools/eight_schools.stan	0.09	0.09	0.98	-2.52% slower
gp_regr/gp_regr.stan	0.21	0.22	0.99	-0.89% slower
irt_2pl/irt_2pl.stan	6.06	6.1	0.99	-0.62% slower
performance.compilation	87.97	87.04	1.01	1.06% faster
low_dim_gauss_mix_collapse/low_dim_gauss_mix_collapse.stan	7.34	7.45	0.99	-1.48% slower
pkpd/one_comp_mm_elim_abs.stan	20.05	21.78	0.92	-8.63% slower
sir/sir.stan	90.32	88.9	1.02	1.57% faster
gp_regr/gen_gp_data.stan	0.04	0.05	0.96	-4.62% slower
low_dim_gauss_mix/low_dim_gauss_mix.stan	2.94	2.95	1.0	-0.07% slower
pkpd/sim_one_comp_mm_elim_abs.stan	0.32	0.31	1.02	1.8% faster
arK/arK.stan	1.73	1.72	1.01	0.85% faster
arma/arma.stan	0.76	0.75	1.01	0.99% faster
garch/garch.stan	0.63	0.63	1.01	0.63% faster
Mean result: 0.990352462614

---

Jenkins Console Log
Blue Ocean
Commit hash: 091ae9c

---

Machine information

ProductName: Mac OS X ProductVersion: 10.11.6 BuildVersion: 15G22010

CPU:
Intel(R) Xeon(R) CPU E5-1680 v2 @ 3.00GHz

G++:
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix

Clang:
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix

[mitzimorris]

looks good! many thanks