We can wrap the random_device as a minstd_rand, a linear congruential
enginer that a lot of C lib uses for rand().
However based on documentation, we should just provides dummy
implementation which throws an exception in the constructor of
random_device [1,2]
But again, compared with run-time exception, a link time error is better
if we simply skip the implementation.
[1]
"explicit random_device(const string& token = implementation-defined );
...
Throws: A value of an implementation-defined type derived from exception
if the random_device could not be initialized."
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/n4659.pdf
section 29.6.6 Class random_device (page 1082)
[2] "Notice that random devices may not always be available to produce
random numbers (and in some systems, they may even never be available).
This is signaled by throwing an exception derived from the standard
exception <http://www.cplusplus.com/exception> on construction
<http://www.cplusplus.com/random_device::random_device> or when a number
is requested with operator()
<http://www.cplusplus.com/random_device::operator%28%29>. "
http://www.cplusplus.com/reference/random/random_device/
Weiming
On 1/2/2018 11:12 AM, Arthur O'Dwyer via Phabricator wrote:
Quuxplusone added a comment.
@weimingz: Since your platform supports `srand(0)`, is it possible to look at how your
platform implements `srand(0)` and "inline" that implementation into
`random_device`? That seems like it would be more in keeping with the other ifdefs in
this file.
I'm confident that constructing an instance of `random_device` MUST NOT
actually call `srand`. (I'd like to say that it shouldn't even call `rand`.)
Either of those calls would be observable by the programmer. But there is a
precedent for e.g. `random_shuffle` making calls to `rand`.
Repository:
rCXX libc++
https://reviews.llvm.org/D41316
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