Question to FLEXC:: rand() [solved]

Reinhard

Hi forumist's,
I'm an user of fastspin/FLEXC
Propeller Spin/PASM Compiler 'FastSpin' (c) 2011-2020 Total Spectrum Software Inc.
Version 4.2.3 Compiled on: Jun 29 2020
In stdlib.h I found
#define RAND_MAX 0x7fff
I make tests i.e.

int z = rand();
printf("%d \n",z);

I get values larger than 0x7FFF.
For a project I need a float random number. So I want to make a way similar this: (float) (rand() / RAND_MAX)
but therefore I need to know the max. Number delivered by rand().

Has anyone an idea ?

Dave Hein

From looking at the source code for the rand function, RAND_MAX should be 0x7fffffff instead of 0x7fff.

ersmith

The flex libraries actually have a built in _randfloat() function (used by BASIC for its rnd() function) which generates a random number between 0.0 and 1.0. Here's an example of its use:

// print some random floating point numbers
#include <stdio.h>

extern float _randfloat(); // built in

void main() {
    for(int i = 0; i < 20; i++) {
        printf("%f\n", _randfloat());
    }
}

evanh

I've always thought floats were inappropriate store of random numbers due to exponent component having no meaning to randomness.

Reinhard

Thank you for all responses.
The randfloat() function is exact what I need.
In the meantime I do this workaround:

int z = (rand() & 0x7FFF);

best regards
Reinhard