add comment to PRNG

lib/utils/prng.py

@@ -3,6 +3,15 @@ from math import ceil
 from itertools import count, chain
 import numpy as np
 
+# Framework for reproducable pseudo-random number generation.
+
+# Unlike python's random module (which uses a stateful generator based on global variables),
+# a counter-mode PRNG like uniformFloats can be used to generate multiple, independent random streams
+# by including an additional parameter before the loop counter.
+# This allows different aspects of an embroidery element to not effect each other's rolls,
+# making random generation resistant to small edits in the control paths or refactoring.
+# Using multiple counters for n-dimentional random streams is also possible and is useful for grid-like structures.
+
 
 def joinArgs(*args):
     # Stringifies parameters into a slash-separated string for use in hash keys.
@@ -15,8 +24,11 @@ MAX_UNIFORM_INT = 2 ** 32 - 1
 
 def uniformInts(*args):
     # Single pseudo-random drawing determined by the joined parameters.
-    # Returns 4 uniformly random uint64.
+    # To get a longer sequence of random numbers, call this loop with a counter as one of the parameters.
+    # Returns 8 uniformly random uint32.
+
     s = joinArgs(*args)
+    # blake2s is python's fastest hash algorithm for small inputs and is designed to be usable as a PRNG.
     h = blake2s(s.encode()).hexdigest()
     nums = []
     for i in range(0, 64, 8):
@@ -25,7 +37,9 @@ def uniformInts(*args):
 
 
 def uniformFloats(*args):
-    # returns an array of 8 floats in the range [0,1]
+    # Single pseudo-random drawing determined by the joined parameters.
+    # To get a longer sequence of random numbers, call this loop with a counter as one of the parameters.
+    # Returns an array of 8 floats in the range [0,1]
     return uniformInts(*args) / MAX_UNIFORM_INT