Custom PRNG binary output

Help & Support
1

I have a prng that i would like to port to crystal.
Testing the output of that prng ( to e.g. dieharder ) requires binary bytes ( 0x00…0xFF).
I came up with this solution.
I was wondering if this is okay for the sole purpose of converting 64bit unsigned integers into raw byte sequence.

2

Hi! Could you provide some code of that random generator, and show where are you needing this? Otherwise it’s not clear how we can help you or what exactly you need.

1 Like
3

Sure!

crprng.cr:

# based on lehmer congruential prng
# it's fast and reasonable secure
# it outputs 8 random bytes per round

def out_put(x)
  STDOUT.write_bytes(x.to_u64, IO::ByteFormat::BigEndian)
end


x_state=0_u128
x_const_small=0xda942042e4dd58b5_u128
x_const_big=0x12e15e35b500f16e2e714eb2b37916a5_u128

x_seed=rand(UInt128::MIN..UInt128::MAX)
loop do
  x_state^=x_seed >> (x_state % 8)
  x_state&*= x_const_big
  x_state&+= x_const_small << (x_state % 8)
  out_put(x_state >> 64)
end

run the prng through dieharder:

crystal build --release ./crprng.cr -o ./crprng.out
./crprng.out | dieharder -g 200 -a
4

The out_put function needs to produce 8bit bytes

5

The standard output is an IO. You can write to it directly:

STDOUT.write_bytes((x_state >> 64).to_u64, IO::ByteFormat::BigEndian)

No need for reopening any integer classes.

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