## File: rounder.go

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golang-gopkg-inf.v0 0.9.1-1
 `123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145` ``````package inf import ( "math/big" ) // Rounder represents a method for rounding the (possibly infinite decimal) // result of a division to a finite Dec. It is used by Dec.Round() and // Dec.Quo(). // // See the Example for results of using each Rounder with some sample values. // type Rounder rounder // See http://speleotrove.com/decimal/damodel.html#refround for more detailed // definitions of these rounding modes. var ( RoundDown Rounder // towards 0 RoundUp Rounder // away from 0 RoundFloor Rounder // towards -infinity RoundCeil Rounder // towards +infinity RoundHalfDown Rounder // to nearest; towards 0 if same distance RoundHalfUp Rounder // to nearest; away from 0 if same distance RoundHalfEven Rounder // to nearest; even last digit if same distance ) // RoundExact is to be used in the case when rounding is not necessary. // When used with Quo or Round, it returns the result verbatim when it can be // expressed exactly with the given precision, and it returns nil otherwise. // QuoExact is a shorthand for using Quo with RoundExact. var RoundExact Rounder type rounder interface { // When UseRemainder() returns true, the Round() method is passed the // remainder of the division, expressed as the numerator and denominator of // a rational. UseRemainder() bool // Round sets the rounded value of a quotient to z, and returns z. // quo is rounded down (truncated towards zero) to the scale obtained from // the Scaler in Quo(). // // When the remainder is not used, remNum and remDen are nil. // When used, the remainder is normalized between -1 and 1; that is: // // -|remDen| < remNum < |remDen| // // remDen has the same sign as y, and remNum is zero or has the same sign // as x. Round(z, quo *Dec, remNum, remDen *big.Int) *Dec } type rndr struct { useRem bool round func(z, quo *Dec, remNum, remDen *big.Int) *Dec } func (r rndr) UseRemainder() bool { return r.useRem } func (r rndr) Round(z, quo *Dec, remNum, remDen *big.Int) *Dec { return r.round(z, quo, remNum, remDen) } var intSign = []*big.Int{big.NewInt(-1), big.NewInt(0), big.NewInt(1)} func roundHalf(f func(c int, odd uint) (roundUp bool)) func(z, q *Dec, rA, rB *big.Int) *Dec { return func(z, q *Dec, rA, rB *big.Int) *Dec { z.Set(q) brA, brB := rA.BitLen(), rB.BitLen() if brA < brB-1 { // brA < brB-1 => |rA| < |rB/2| return z } roundUp := false srA, srB := rA.Sign(), rB.Sign() s := srA * srB if brA == brB-1 { rA2 := new(big.Int).Lsh(rA, 1) if s < 0 { rA2.Neg(rA2) } roundUp = f(rA2.Cmp(rB)*srB, z.UnscaledBig().Bit(0)) } else { // brA > brB-1 => |rA| > |rB/2| roundUp = true } if roundUp { z.UnscaledBig().Add(z.UnscaledBig(), intSign[s+1]) } return z } } func init() { RoundExact = rndr{true, func(z, q *Dec, rA, rB *big.Int) *Dec { if rA.Sign() != 0 { return nil } return z.Set(q) }} RoundDown = rndr{false, func(z, q *Dec, rA, rB *big.Int) *Dec { return z.Set(q) }} RoundUp = rndr{true, func(z, q *Dec, rA, rB *big.Int) *Dec { z.Set(q) if rA.Sign() != 0 { z.UnscaledBig().Add(z.UnscaledBig(), intSign[rA.Sign()*rB.Sign()+1]) } return z }} RoundFloor = rndr{true, func(z, q *Dec, rA, rB *big.Int) *Dec { z.Set(q) if rA.Sign()*rB.Sign() < 0 { z.UnscaledBig().Add(z.UnscaledBig(), intSign[0]) } return z }} RoundCeil = rndr{true, func(z, q *Dec, rA, rB *big.Int) *Dec { z.Set(q) if rA.Sign()*rB.Sign() > 0 { z.UnscaledBig().Add(z.UnscaledBig(), intSign[2]) } return z }} RoundHalfDown = rndr{true, roundHalf( func(c int, odd uint) bool { return c > 0 })} RoundHalfUp = rndr{true, roundHalf( func(c int, odd uint) bool { return c >= 0 })} RoundHalfEven = rndr{true, roundHalf( func(c int, odd uint) bool { return c > 0 || c == 0 && odd == 1 })} } ``````