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67 lines
2.4 KiB
67 lines
2.4 KiB
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(in-package :cl-rng)
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(defparameter *default-precision* 1
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"Default precision for the default RNG provider")
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(defparameter *default-randomness-provider* #'(lambda (&rest args) (apply #'crandom (append `(:precision ,*default-precision*) args)))
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"The default randomness provider used by cl-rng functions")
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(defun chance (fraction &key (provider *default-randomness-provider*))
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"Returns T if chance fraction is met"
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(< (funcall provider) fraction))
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(defun weighted (weights &key (default nil) (provider *default-randomness-provider*))
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"Interpret weights as an alist where the key is the item and the value is the chance. If no chances are met, return default"
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(let ((previous 0)
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(result (funcall provider))
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(rval default))
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(mapc (lambda (x)
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(let ((value (car x))
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(weight (cdr x)))
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(and (>= result previous)
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(<= result (+ previous weight))
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(setf rval value))
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(incf previous weight)))
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weights)
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(values rval result)))
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(export 'weighted)
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(defun shuffle! (sequence &key (provider *default-randomness-provider*))
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"In-place shuffle a sequence"
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(if (listp sequence)
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(loop for i from (1- (length sequence)) above 0 do
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(rotatef (nth i sequence)
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(nth (funcall provider :limit i :transform #'floor) sequence)))
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(loop for i from (1- (length sequence)) above 0 do
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(rotatef (aref sequence i)
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(aref sequence (funcall provider :limit i :transform #'floor)))))
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sequence)
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(defun within (sequence &key (provider *default-randomness-provider*))
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"A random value withing a sequence. Can be setf()'d"
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(if (listp sequence)
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(nth (funcall provider :limit (1- (length sequence)) :transform 'round) sequence)
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(aref sequence (funcall provider :limit (1- (length sequence)) :transform 'round))))
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(defun within-set (sequence value)
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(let ((index (funcall *default-randomness-provider* :limit (1- (length sequence)) :transform 'round)))
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(if (listp sequence)
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(setf (nth index sequence) value)
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(setf (aref sequence index) value))))
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(defun range (start end &key (integral nil) (provider *default-randomness-provider*))
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"A random number in a range"
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(+ start (funcall provider :limit (- end start) :transform (if integral 'round 'identity))))
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;; Exports
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(export '*default-randomness-provider*)
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(export '*default-precision*)
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(defsetf within within-set)
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(export 'range)
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(export 'within)
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(export 'shuffle!)
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(export 'chance)
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