45 lines
1.2 KiB
Go
45 lines
1.2 KiB
Go
package dectofrac
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import (
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"math"
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"math/big"
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)
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// MaxIterations is some sane limit of iterations for precision mode
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const MaxIterations = 5000
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// NewRatI returns rational from decimal
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// using `iterations` number of iterations in Continued Fraction algorythm
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func NewRatI(val float64, iterations int64) *big.Rat {
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return NewRat(val, iterations, 0)
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}
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// NewRatP returns rational from decimal
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// by going as mush iterations, until next fraction is less than `stepPrecision`
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func NewRatP(val float64, stepPrecision float64) *big.Rat {
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return NewRat(val, MaxIterations, stepPrecision)
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}
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func NewRat(val float64, iterations int64, stepPrecision float64) *big.Rat {
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a0 := int64(math.Floor(val))
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x0 := val - float64(a0)
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rat := cf(x0, 1, iterations, stepPrecision)
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return rat.Add(rat, new(big.Rat).SetInt64(a0))
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}
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func cf(xi float64, i int64, limit int64, stepPrecision float64) *big.Rat {
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if i >= limit || xi <= stepPrecision {
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return big.NewRat(0, 1)
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}
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inverted := 1 / xi
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aj := int64(math.Floor(inverted))
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xj := inverted - float64(aj)
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ratAJ := new(big.Rat).SetInt64(aj)
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ratNext := cf(xj, i+1, limit, stepPrecision)
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res := ratAJ.Add(ratAJ, ratNext)
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res = res.Inv(res)
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return res
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}
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