623e513 · rowtype-yoga/purescript-fixed-precision

git.iko.soy/rowtype-yoga/purescript-fixed-precision

Add 'rescale' (#25)

commit623e5136f3eb9a92f002b79692c3fd55406b5086 authorHarry Garrood <harry@garrood.me> dateWed 4 Mar 2020, 21:22 (7 years ago) parentabd54d5

2 files changed+65−2

compare with main

unifiedsplit

src/Data/Fixed.purs+14−1 test/Main.purs+51−1

src/Data/Fixed.purs+14−1

@@ -15,6 +15,7 @@ module Data.Fixed

1515 , floor

1616 , ceil

1717 , round

18+ , rescale

1819 , approxDiv

1920 , kind Precision

2021 , One

@@ -40,11 +41,12 @@ import Data.Array (replicate)

4041import Data.BigInt (BigInt)

4142import Data.BigInt as BigInt

4243import Data.Int as Int

43−import Data.Maybe (Maybe(..))

44+import Data.Maybe (Maybe(..), fromJust)

4445import Data.Monoid as Monoid

4546import Data.String.CodeUnits as StringCU

4647import Data.String as String

4748import Math as Math

49+import Partial.Unsafe (unsafePartial)

4850import Prim.TypeError (class Warn, Text)

4951

5052-- | A kind for type-level precision information

@@ -294,6 +296,17 @@ round n = Fixed (numerator n + x) where

294296 | m * BigInt.fromInt 2 >= d = d - m

295297 | otherwise = -m

296298

299+-- | Change the precision of a fixed-point number. If the new precision is

300+-- | less than the old precision, extra decimal places will be lost.

301+rescale

302+ :: forall precision1 precision2

303+ . KnownPrecision precision1

304+ => KnownPrecision precision2

305+ => Fixed precision1

306+ -> Fixed precision2

307+rescale =

308+ unsafePartial (fromJust <<< fromString <<< toString)

309+

297310-- | Division of fixed-precision numbers. This function is deprecated; you

298311-- | should use `/` from the `EuclideanRing` instance instead.

299312approxDiv

test/Main.purs+51−1

@@ -2,7 +2,7 @@ module Test.Main where

33import Prelude

5−import Data.Fixed (class KnownPrecision, Fixed, PProxy, fromNumber, toNumber, fromString, reifyPrecision, reflectPrecision, toString, P100)

5+import Data.Fixed (class KnownPrecision, Fixed, PProxy, fromNumber, toNumber, fromString, reifyPrecision, reflectPrecision, toString, P100, rescale, fromBigInt, floor)

66import Data.BigInt as BigInt

77import Data.Maybe (Maybe(..), fromJust, isJust)

88import Effect (Effect)

@@ -27,6 +27,28 @@ fromNumberWith

2727 -> Maybe (Fixed precision)

2828fromNumberWith _ = fromNumber

2929

30+-- | For type hinting.

31+withPrecisionOf

32+ :: forall precision

33+ . PProxy precision

34+ -> Fixed precision

35+ -> Fixed precision

36+withPrecisionOf _ x = x

37+

38+floorToPrecision

39+ :: forall precision

40+ . KnownPrecision precision

41+ => Int

42+ -> Fixed precision

43+ -> Fixed precision

44+floorToPrecision p =

45+ (_ / scaleFactor)

46+ <<< floor

47+ <<< (_ * scaleFactor)

48+ where

49+ scaleFactor =

50+ fromBigInt (BigInt.pow (BigInt.fromInt 10) (BigInt.fromInt p))

51+

3052main :: Effect Unit

3153main = do

3254 log "Commutative monoid under addition:"

@@ -123,3 +145,31 @@ main = do

123145 Nothing ->

124146 false

125147 <?> ("failed to roundtrip via Number: " <> show { precision, x })

148+

149+ log ""

150+ log "rescale"

151+ log ""

152+

153+ log "rescaling up then down should be no-op"

154+ quickCheck' 1000 do

155+ let lo = 10

156+ hi <- chooseInt 10 20

157+ unsafePartial fromJust $ join $

158+ reifyPrecision lo \lo_ ->

159+ reifyPrecision hi \hi_ -> do

160+ x <- genFixedP lo_

161+ let y = withPrecisionOf hi_ $ rescale x

162+ let xx = rescale y

163+ pure $ x == xx <?> show { x, xx, y }

164+

165+ log "rescaling down then up should be the same as flooring"

166+ quickCheck' 1000 do

167+ let hi = 20

168+ lo <- chooseInt 10 20

169+ unsafePartial fromJust $ join $

170+ reifyPrecision lo \lo_ ->

171+ reifyPrecision hi \hi_ -> do

172+ x <- genFixedP hi_

173+ let y = withPrecisionOf lo_ $ rescale x

174+ let xx = floorToPrecision lo x

175+ pure $ xx == rescale y <?> show { x, xx, y }