-- | 
-- Module: Statistics
-- Description: Basic bounded statistics
-- Copyright: (c) 2011 National Institute of Aerospace / Galois, Inc.
--
-- Basic bounded statistics.  In the following, a bound @n@ is given stating
-- the number of periods over which to compute the statistic (@n == 1@ computes
-- it only over the current period).

{-# LANGUAGE NoImplicitPrelude #-}

module Copilot.Library.Statistics
    ( max, min, sum, mean, meanNow ) where

import Copilot.Language
import Copilot.Library.Utils

-- | Summation.
sum :: ( Typed a, Num a, Eq a ) => Int -> Stream a -> Stream a
sum n s = nfoldl1 n (+) s

-- | Maximum value.
max :: ( Typed a, Ord a ) => Int -> Stream a -> Stream a
max n s = nfoldl1 n largest s
    where largest  = \ x y -> mux ( x >= y ) x y

-- | Minimum value.
min :: ( Typed a, Ord a ) => Int -> Stream a -> Stream a
min n s = nfoldl1 n smallest s
    where smallest = \ x y -> mux ( x <= y ) x y

-- | Mean value.  @n@ must not overflow
-- for word size @a@ for streams over which computation is peformed.
mean :: ( Typed a, Eq a, Fractional a ) => Int -> Stream a -> Stream a
mean n s = ( sum n s ) / ( fromIntegral n )

-- | Mean value over the current set of streams passed in.
meanNow :: ( Typed a, Integral a ) => [ Stream a ] -> Stream a
meanNow [] = 
  badUsage "list of arguments to meanNow must be nonempty"
meanNow ls = ( foldl1 (+) ls ) `div` ( fromIntegral $ length ls )
