Use custom rand()

[krychu]

This is an issue to find the best replacement for stdlib rand(). It'll be great to enjoy all the benefits but care needs to be taken to ensure good quality of the implementation as it directly impact the quality of generated images.

Rationale:

• Better performance: speed and quality
• Stability across platforms / different stdlibs
• Don't alter rand() sequence in case the user app relies on it

Reference material

• GDC: Noise-Based RNG
• Used by @ggcrunchy https://www.math.uni-bielefeld.de/~sillke/ALGORITHMS/random/marsaglia-c

/cc @ggcrunchy, @ggsg-francis

[krychu]

Notable info from the GDC talk:

[krychu]

There were some issues with the squirrel function discovered, which led to an improved implementation:
https://twitter.com/squirreltweets/status/1421251894274625536?lang=en

The new implementation does involve two more noise numbers (5 instead of 3) and two more bit shifts (5 instead of 3). So the performance characteristics will change.

[krychu]

Shortlist:

• Squirrel 3
• Squirrel 5
• xors128
• xorshift1
• Marsaglia