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(*
* A simple fixed point datatype
*
* -- Allen
*)
functor FixedPoint (val decimal_bits : int) : FIXED_POINT =
struct
structure W = Word31
infix << >>
infix & ||
val decimal_places = (decimal_bits + 2) div 3
val realToString = Real.fmt (StringCvt.FIX(SOME decimal_places))
val op<< = W.<<
val op>> = W.>>
val op& = W.andb
val op|| = W.orb
val op div = W.div
val word = W.fromInt
val int = W.toInt
type fixed_point = W.word
val bits = word decimal_bits
val bits2 = bits >> 0w1
val bits4 = bits >> 0w2
val zero = 0w0
val one = 0w1 << bits
val realOne = Real.fromInt(int one)
val compare = W.compare
val op* = fn(i:fixed_point,j:fixed_point) => W.*(i >> bits2,j >> bits2)
val op/ = fn(i:fixed_point,j:fixed_point) => (i << bits) div j
val mask = one - 0w1
fun fromInt i = (word i) << bits
fun fixed_point(a,b) = let val b' = word b
in (((word a) << bits) + (b' >> 0w1)) div b' end
fun fromReal r = word(Real.round(Real.*(r, realOne)))
fun toReal p = Real./(Real.fromInt(int p), realOne)
fun toWord f = f
fun toString p = realToString(toReal p)
handle Overflow => "inf"
fun scale(i,j) = W.*(i, word j)
fun i div j = W.div(i,word j)
val min = W.min
val max = W.max
end
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