How to generate a random number from system clock as seed (page 2)

{ const seed = castFrom!long.to!uint(Clock.currStdTime); auto rng = Random(seed); auto result = generate!(() => uniform(0, 10, rng))().take(7); // new random numbers sequence every time result.writeln; } }

June 09

Re: How to generate a random number from system clock as seed

Posted by Eric P626
in reply to Joseph Rushton Wakeling

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Eric P626

Posted in reply to Joseph Rushton Wakeling

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On Sunday, 9 June 2024 at 13:20:09 UTC, Joseph Rushton Wakeling wrote:

On Saturday, 8 June 2024 at 16:09:04 UTC, monkyyy wrote:

rng is an optional parameter, uniform(0,100).writeln; alone works; the docs not telling you that is really bad

The docs do tell you that rng is an optional parameter of

I don't need anything fancy. Most of the time, it's for video games, so I want to make sure the numbers are always shuffled. Here it's for maze generation, so I wan each maze to be unique.

Eventually, I would like to use a fixed seed generator, so that I can generate the same maze over and over again if necessary. I guess, in that case, I could create a generator.

I found the the simplest way to implement this is not to define any seed or generator and simply call:

uniform(0,2)

with the range you want. It was a bit counter intuitive because most languages have a rand() function. But I prefer specifying a range.

Thanks again.

On 09.06.2024 16:37, Eric P626 wrote: > On Saturday, 8 June 2024 at 18:25:20 UTC, drug007 wrote: >> >> ~~~ >> { >> const seed = castFrom!long.to!uint(Clock.currStdTime); >> auto rng = Random(seed); >> auto result = generate!(() => uniform(0, 10, rng))().take(7); >> // new random numbers sequence every time >> result.writeln; >> } >> } >> ~~~ > > I managed to use this piece of code and it worked. > > ~~~ > uint seed = castFrom!long.to!uint(Clock.currStdTime); > auto rng = Random(seed); > ~~~ > > I am not exactly sure what the exclamation points stand for in the first line of code. Probably, defining a type to class ```castFrom``` and function ```to```. But I get the idea that it just cast long to uint since ```Random``` requires an unsigned int > > I assume from this line of code that C casting like ```(uint)varname``` would not work. > > `CastFrom!long` is a template instantiation. The instantiated template converts from `long` to `uint`. It is useful in meta-programming but here you can safely use other forms like c style cast: ```d const seed = cast(uint) Clock.currStdTime; ``` or ``` const seed = to!uint(Clock.currStdTime & 0xFFFF); ``` here we need to use the `0xFFFF` mask, because `to!uint` throws a conversion positive overflow when the value of `Clock.currStdTime` exceeds the value of `uint.max`. But I don't like this variant and I don't recommend it.

On Saturday, 8 June 2024 at 13:19:30 UTC, Eric P626 wrote:

I managed to create a random number generator using the following code:

auto rng = Random(42);
//....
uniform(0,10,rng);

Now I want to seed the generator using system time. I looked at Date & time functions/classes and systime functions/classes. The problem is that they all require a time zone. But I don't need a time zone since there is no time zone. I just want the number of seconds elapsed since jan 1st 1970. In other words, the internal system clock value.

I'm not sure if anyone said it explicitly, but uniform(0, 10) uses the default RNG rndGen, which is already properly seeded with an unpredictable seed:

Global random number generator used by various functions in this module whenever no generator is specified. It is allocated per-thread and initialized to an unpredictable value for each thread.

So unless you are explicitly doing something like saving the seed for future playback, I'd leave it off.

-Steve

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