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a1bed2f5fe | ||
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2b68c56fe0 |
2 changed files with 17 additions and 6 deletions
22
decimal.go
22
decimal.go
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@ -129,11 +129,10 @@ func NewFromBigInt(value *big.Int, exp int32) Decimal {
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//
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//
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// Example:
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// Example:
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//
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//
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// d1 := NewFromBigRat(big.NewRat(0, 1), 0) // output: "0"
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// d1 := NewFromBigRat(big.NewRat(0, 1), 0) // output: "0"
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// d2 := NewFromBigRat(big.NewRat(4, 5), 1) // output: "0.8"
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// d2 := NewFromBigRat(big.NewRat(4, 5), 1) // output: "0.8"
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// d3 := NewFromBigRat(big.NewRat(1000, 3), 3) // output: "333.333"
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// d3 := NewFromBigRat(big.NewRat(1000, 3), 3) // output: "333.333"
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// d4 := NewFromBigRat(big.NewRat(2, 7), 4) // output: "0.2857"
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// d4 := NewFromBigRat(big.NewRat(2, 7), 4) // output: "0.2857"
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//
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func NewFromBigRat(value *big.Rat, precision int32) Decimal {
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func NewFromBigRat(value *big.Rat, precision int32) Decimal {
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return Decimal{
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return Decimal{
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value: new(big.Int).Set(value.Num()),
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value: new(big.Int).Set(value.Num()),
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@ -920,7 +919,10 @@ func (d Decimal) Ln(precision int32) (Decimal, error) {
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// Halley's Iteration.
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// Halley's Iteration.
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// Calculating n-th term of formula: a_(n+1) = a_n - 2 * (exp(a_n) - z) / (exp(a_n) + z),
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// Calculating n-th term of formula: a_(n+1) = a_n - 2 * (exp(a_n) - z) / (exp(a_n) + z),
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// until the difference between current and next term is smaller than epsilon
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// until the difference between current and next term is smaller than epsilon
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for {
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var prevStep Decimal
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maxIters := calcPrecision*2 + 10
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for i := int32(0); i < maxIters; i++ {
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// exp(a_n)
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// exp(a_n)
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comp3, _ = comp1.ExpTaylor(calcPrecision)
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comp3, _ = comp1.ExpTaylor(calcPrecision)
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// exp(a_n) - z
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// exp(a_n) - z
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@ -934,9 +936,17 @@ func (d Decimal) Ln(precision int32) (Decimal, error) {
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// comp1 = a_(n+1) = a_n - 2 * (exp(a_n) - z) / (exp(a_n) + z)
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// comp1 = a_(n+1) = a_n - 2 * (exp(a_n) - z) / (exp(a_n) + z)
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comp1 = comp1.Sub(comp3)
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comp1 = comp1.Sub(comp3)
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if prevStep.Add(comp3).IsZero() {
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// If iteration steps oscillate we should return early and prevent an infinity loop
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// NOTE(mwoss): This should be quite a rare case, returning error is not necessary
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break
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}
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if comp3.Abs().Cmp(epsilon) <= 0 {
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if comp3.Abs().Cmp(epsilon) <= 0 {
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break
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break
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}
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}
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prevStep = comp3
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}
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}
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}
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}
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@ -2863,6 +2863,7 @@ func TestDecimal_Ln(t *testing.T) {
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{"839101.0351094726488848490572028502", 50, "13.64008640145229044389152437468283605382056561604272"},
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{"839101.0351094726488848490572028502", 50, "13.64008640145229044389152437468283605382056561604272"},
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{"5023583755703750094849.03519358513093500275017501750602739169823", 25, "49.9684305274348922267409953"},
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{"5023583755703750094849.03519358513093500275017501750602739169823", 25, "49.9684305274348922267409953"},
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{"5023583755703750094849.03519358513093500275017501750602739169823", -1, "50.0"},
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{"5023583755703750094849.03519358513093500275017501750602739169823", -1, "50.0"},
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{"66.12", 18, "4.191471272952823429"},
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} {
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} {
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d, _ := NewFromString(testCase.Dec)
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d, _ := NewFromString(testCase.Dec)
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expected, _ := NewFromString(testCase.Expected)
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expected, _ := NewFromString(testCase.Expected)
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