module Numeric(fromRat,
showSigned, showInt,
readSigned, readInt,
readDec, readOct, readHex,
floatToDigits,
showEFloat, showFFloat, showGFloat, showFloat,
readFloat, lexDigits) where
import Prelude
import Char
import Ratio
import Array
default()
-- This converts a rational to a floating. This should be used in the
-- Fractional instances of Float and Double.
fromRat :: (RealFloat a) => Rational -> a
fromRat x =
if x == 0 then encodeFloat 0 0 -- Handle exceptional cases
else if x < 0 then - fromRat' (-x) -- first.
else fromRat' x
-- Conversion process:
-- Scale the rational number by the RealFloat base until
-- it lies in the range of the mantissa (as used by decodeFloat/encodeFloat).
-- Then round the rational to an Integer and encode it with the exponent
-- that we got from the scaling.
-- To speed up the scaling process we compute the log2 of the number to get
-- a first guess of the exponent.
fromRat' :: (RealFloat a) => Rational -> a
fromRat' x = undefined{-r
where b = floatRadix r
p = floatDigits r
(minExp0, _) = floatRange r
minExp = minExp0 - p -- the real minimum exponent
xMin = toRational (expt b (p-1))
xMax = toRational (expt b p)
p0 = (integerLogBase b (numerator x) -
integerLogBase b (denominator x) - p) `max` minExp
f = if p0 < 0 then 1 % expt b (-p0) else expt b p0 % 1
(x', p') = scaleRat (toRational b) minExp xMin xMax p0 (x / f)
r = encodeFloat (round x') p'-}
-- Scale x until xMin <= x < xMax, or p (the exponent) <= minExp.
scaleRat :: Rational -> Int -> Rational -> Rational ->
Int -> Rational -> (Rational, Int)
scaleRat b minExp xMin xMax p x =
if p <= minExp then
(x, p)
else if x >= xMax then
scaleRat b minExp xMin xMax (p+1) (x/b)
else if x < xMin then
scaleRat b minExp xMin xMax (p-1) (x*b)
else
(x, p)
-- Exponentiation with a cache for the most common numbers.
minExpt = 0::Int
maxExpt = 1100::Int
expt :: Integer -> Int -> Integer
expt base n =
if base == 2 && n >= minExpt && n <= maxExpt then
expts!n
else
base^n
expts :: Array Int Integer
expts = array (minExpt,maxExpt) [(n,2^n) | n <- [minExpt .. maxExpt]]
-- Compute the (floor of the) log of i in base b.
-- Simplest way would be just divide i by b until it's smaller then b,
-- but that would be very slow! We are just slightly more clever.
integerLogBase :: Integer -> Integer -> Int
integerLogBase b i =
if i < b then
0
else
-- Try squaring the base first to cut down the number of divisions.
let l = 2 * integerLogBase (b*b) i
doDiv :: Integer -> Int -> Int
doDiv i l = if i < b then l else doDiv (i `div` b) (l+1)
in doDiv (i `div` (b^l)) l
-- Misc utilities to show integers and floats
showSigned :: Real a => (a -> ShowS) -> Int -> a -> ShowS
showSigned showPos p x | x < 0 = showParen (p > 6)
(showChar '-' . showPos (-x))
| otherwise = showPos x
-- showInt is used for positive numbers only
showInt :: Integral a => a -> ShowS
--showInt :: Integral a => a -> String->String -- for hs2alfa
showInt n r | n < 0 = error "Numeric.showInt: can't show negative numbers"
| otherwise =
let (n',d) = quotRem n 10
r' = chr (fromEnum '0' + fromIntegral d) : r
in if n' == 0 then r' else showInt n' r'
readSigned :: (Real a) => ReadS a -> ReadS a
readSigned readPos = readParen False read'
where read' r = read'' r ++
[(-x,t) | ("-",s) <- lex r,
(x,t) <- read'' s]
read'' r = [(n,s) | (str,s) <- lex r,
(n,"") <- readPos str]
-- readInt reads a string of digits using an arbitrary base.
-- Leading minus signs must be handled elsewhere.
readInt :: (Integral a) => a -> (Char -> Bool) -> (Char -> Int) -> ReadS a
readInt radix isDig digToInt s =
[(foldl1 (\n d -> n * radix + d) (map (fromIntegral . digToInt) ds), r)
| (ds,r) <- nonnull isDig s ]
-- Unsigned readers for various bases
readDec, readOct, readHex :: (Integral a) => ReadS a
readDec = readInt 10 isDigit digitToInt
readOct = readInt 8 isOctDigit digitToInt
readHex = readInt 16 isHexDigit digitToInt
showEFloat :: (RealFloat a) => Maybe Int -> a -> ShowS
showFFloat :: (RealFloat a) => Maybe Int -> a -> ShowS
showGFloat :: (RealFloat a) => Maybe Int -> a -> ShowS
showFloat :: (RealFloat a) => a -> ShowS
showEFloat d x = showString (formatRealFloat FFExponent d x)
showFFloat d x = showString (formatRealFloat FFFixed d x)
showGFloat d x = showString (formatRealFloat FFGeneric d x)
showFloat = showGFloat Nothing
-- These are the format types. This type is not exported.
data FFFormat = FFExponent | FFFixed | FFGeneric
formatRealFloat :: (RealFloat a) => FFFormat -> Maybe Int -> a -> String
formatRealFloat fmt decs x = s
where base = 10
s = if isNaN x then
"NaN"
else if isInfinite x then
if x < 0 then "-Infinity" else "Infinity"
else if x < 0 || isNegativeZero x then
'-' : doFmt fmt (floatToDigits (toInteger base) (-x))
else
doFmt fmt (floatToDigits (toInteger base) x)
doFmt fmt (is, e) =
let ds = map intToDigit is
in case fmt of
FFGeneric ->
doFmt (if e < 0 || e > 7 then FFExponent else FFFixed)
(is, e)
--{ -
FFExponent ->
case decs of
Nothing ->
case ds of
['0'] -> "0.0e0"
[d] -> d : ".0e" ++ show (e-1)
d:ds -> d : '.' : ds ++ 'e':show (e-1)
Just dec ->
let dec' = max dec 1 in
case is of
[0] -> '0':'.':take dec' (repeat '0') ++ "e0"
_ ->
let (ei, is') = roundTo base (dec'+1) is
d:ds = map intToDigit
(if ei > 0 then init is' else is')
in d:'.':ds ++ "e" ++ show (e-1+ei)
FFFixed ->
case decs of
Nothing ->
let f 0 s ds = mk0 s ++ "." ++ mk0 ds
f n s "" = f (n-1) (s++"0") ""
f n s (d:ds) = f (n-1) (s++[d]) ds
mk0 "" = "0"
mk0 s = s
in f e "" ds
Just dec ->
let dec' = max dec 0 in
if e >= 0 then
let (ei, is') = roundTo base (dec' + e) is
(ls, rs) = splitAt (e+ei) (map intToDigit is')
in (if null ls then "0" else ls) ++
(if null rs then "" else '.' : rs)
else
let (ei, is') = roundTo base dec'
(replicate (-e) 0 ++ is)
d : ds = map intToDigit
(if ei > 0 then is' else 0:is')
in d : '.' : ds
--}
roundTo :: Int -> Int -> [Int] -> (Int, [Int])
roundTo base d is = case f d is of
(x, is)
| x==0 -> (0, is)
| x==1 -> (1, 1 : is)
where b2 = base `div` 2
f n [] = (0, replicate n 0)
f 0 (i:_) = (if i >= b2 then 1 else 0, [])
f d (i:is) =
let (c, ds) = f (d-1) is
i' = c + i
in if i' == base then (1, 0:ds) else (0, i':ds)
--
-- Based on "Printing Floating-Point Numbers Quickly and Accurately"
-- by R.G. Burger and R. K. Dybvig, in PLDI 96.
-- This version uses a much slower logarithm estimator. It should be improved.
-- This function returns a list of digits (Ints in [0..base-1]) and an
-- exponent.
floatToDigits :: (RealFloat a) => Integer -> a -> ([Int], Int)
floatToDigits _ 0 = ([0], 0)
floatToDigits base x =
let (f0, e0) = decodeFloat x
(minExp0, _) = floatRange x
p = floatDigits x
b = floatRadix x
minExp = minExp0 - p -- the real minimum exponent
-- Haskell requires that f be adjusted so denormalized numbers
-- will have an impossibly low exponent. Adjust for this.
(f, e) = let n = minExp - e0
in if n > 0 then (f0 `div` (b^n), e0+n) else (f0, e0)
(r, s, mUp, mDn) =
if e >= 0 then
let be = b^e in
if f == b^(p-1) then
(f*be*b*2, 2*b, be*b, b)
else
(f*be*2, 2, be, be)
else
if e > minExp && f == b^(p-1) then
(f*b*2, b^(-e+1)*2, b, 1)
else
(f*2, b^(-e)*2, 1, 1)
k =
let k0 =
if b==2 && base==10 then
-- logBase 10 2 is slightly bigger than 3/10 so
-- the following will err on the low side. Ignoring
-- the fraction will make it err even more.
-- Haskell promises that p-1 <= logBase b f < p.
(p - 1 + e0) * 3 `div` 10
else
ceiling ((log (fromInteger (f+1)::Double) +
fromIntegral e * log (fromInteger b)) /
log (fromInteger base))
fixup n =
if n >= 0 then
if r + mUp <= expt base n * s then n else fixup (n+1)
else
if expt base (-n) * (r + mUp) <= s then n
else fixup (n+1)
in fixup k0
gen ds rn sN mUpN mDnN =
let (dn, rn') = (rn * base) `divMod` sN
mUpN' = mUpN * base
mDnN' = mDnN * base
in case (rn' < mDnN', rn' + mUpN' > sN) of
(True, False) -> dn : ds
(False, True) -> dn+1 : ds
(True, True) -> if rn' * 2 < sN then dn : ds else dn+1 : ds
(False, False) -> gen (dn:ds) rn' sN mUpN' mDnN'
rds =
if k >= 0 then
gen [] r (s * expt base k) mUp mDn
else
let bk = expt base (-k)
in gen [] (r * bk) s (mUp * bk) (mDn * bk)
in (map fromIntegral (reverse rds), k)
-- This floating point reader uses a less restrictive syntax for floating
-- point than the Haskell lexer. The `.' is optional.
readFloat :: (RealFloat a) => ReadS a
readFloat r = [(fromRational ((n%1)*10^^(k-d)),t) | (n,d,s) <- readFix r,
(k,t) <- readExp s]
where readFix r = [(read (ds++ds'), length ds', t)
| (ds,d) <- lexDigits r,
(ds',t) <- lexFrac d ]
lexFrac ('.':ds) = lexDigits ds
lexFrac s = [("",s)]
readExp (e:s) | e `elem` "eE" = readExp' s
readExp s = [(0,s)]
readExp' ('-':s) = [(-k,t) | (k,t) <- readDec s]
readExp' ('+':s) = readDec s
readExp' s = readDec s
lexDigits :: ReadS String
lexDigits = nonnull isDigit
nonnull :: (Char -> Bool) -> ReadS String
nonnull p s = [(cs,t) | (cs@(_:_),t) <- [span p s]]