Fantom-foundation/go-lachesis

package piecefunc

const (
    // PercentUnit is used to define ratios with integers, it's 1.0
    PercentUnit = 1e6
)

// Dot is a pair of numbers
type Dot struct {
    X uint64
    Y uint64
}

// Mul is multiplication of ratios with integer numbers
func Mul(a, b uint64) uint64 {
    return a * b / PercentUnit
}

// Div is division of ratios with integer numbers
func Div(a, b uint64) uint64 {
    return a * PercentUnit / b
}

// Get calculates f(x), where f is a piecewise linear function defined by the pieces
func Get(x uint64, pieces []Dot) uint64 {

    // find a piece
    p0 := len(pieces) - 2
    for i, piece := range pieces {
        if i >= 1 && i < len(pieces)-1 && piece.X > x {
            p0 = i - 1
            break
        }
    }

    // linearly interpolate
    p1 := p0 + 1

    ratio := Div(x-pieces[p0].X, pieces[p1].X-pieces[p0].X)

    return Mul(pieces[p0].Y, (PercentUnit-ratio)) + Mul(pieces[p1].Y, ratio)
}