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Author SHA1 Message Date
Leo
870c906735
Merge aa070c4ec8 into 57a340d853 2024-01-31 11:44:02 +01:00
Leonardo
aa070c4ec8 make Sqrt a method of Decimal; add unit tests (1 failing) 2021-03-27 13:52:30 -07:00
Leonardo Cicconi
a68916bc93 added Sqrt and SqrtRound functions 2021-03-25 17:42:49 -07:00
2 changed files with 91 additions and 0 deletions

View file

@ -19,6 +19,7 @@ package decimal
import ( import (
"database/sql/driver" "database/sql/driver"
"encoding/binary" "encoding/binary"
"errors"
"fmt" "fmt"
"math" "math"
"math/big" "math/big"
@ -2006,3 +2007,59 @@ func (d Decimal) Tan() Decimal {
} }
return y return y
} }
// More math
// Sqrt returns the square root of d, accurate to DivisionPrecision decimal places.
// Sqrt is only valid for non-negative numbers; it will return an error otherwise.
func (d Decimal) Sqrt() (Decimal, error) {
s, _, err := d.SqrtRound(int32(DivisionPrecision))
return s, err
}
// ErrImaginaryResult indicates an operation that would produce an imaginary result.
var ErrImaginaryResult = errors.New("The result of this operation is imaginary.")
// SqrtMaxIter sets a limit for number of iterations for the Sqrt function
const SqrtMaxIter = 1000000
// SqrtRound returns the square root of d, accurate to precision decimal places.
// The bool precise returns whether the precision was achieved.
// SqrtRound is only valid for non-negative numbers; it will return an error otherwise.
func (d Decimal) SqrtRound(precision int32) (Decimal, bool, error) {
var (
maxError = New(1, -precision)
one = NewFromFloat(1)
lo, hi Decimal
)
// Handle cases where d < 0, d = 0, 0 < d < 1, and d > 1
if d.GreaterThanOrEqual(one) {
lo = Zero
hi = d
} else if d.Equal(one) {
return one, true, nil
} else if d.LessThan(Zero) {
return Zero, false, ErrImaginaryResult
} else if d.Equal(Zero) {
return Zero, true, nil
} else {
// d is between 0 and 1. Therefore, 0 < d < Sqrt(d) < 1.
lo = d
hi = one
}
var mid Decimal
for i := 0; i < SqrtMaxIter; i++ {
mid = lo.Add(hi).Div(New(2, 0)) //mid = (lo+hi)/2;
if mid.Mul(mid).Sub(d).Abs().LessThan(maxError) {
return mid, true, nil
}
if mid.Mul(mid).GreaterThan(d) {
hi = mid
} else {
lo = mid
}
}
return mid, false, nil
}

View file

@ -3194,6 +3194,40 @@ func TestAvg(t *testing.T) {
} }
} }
func TestSqrtRound(t *testing.T) {
i := NewFromFloat(-1)
if _, err := i.Sqrt(); err != ErrImaginaryResult {
t.Errorf("Square root of -1 should produce error")
}
var vals = map[string]string{
// value : Sqrt(value)
"0.0": "0.0",
"0.002342": "0.0483942145302514",
"1.0": "1.0",
"3.0": "1.7320508075688773",
"4.0": "2.0",
"4.5": "2.1213203435596426",
"3289854.0": "1813.7954680724064485",
}
for val, expected := range vals {
v, err := NewFromString(val)
if err != nil {
t.Errorf("error parsing test value into Decimal")
}
e, err := NewFromString(expected)
if err != nil {
t.Errorf("error parsing test expected value into Decimal")
}
if sqrt, err := v.Sqrt(); err != nil || !sqrt.Equal(e) {
t.Errorf("Square root of %s should be %s, not %s (error: %s)", v, e, sqrt, err)
}
}
}
func TestRoundBankAnomaly(t *testing.T) { func TestRoundBankAnomaly(t *testing.T) {
a := New(25, -1) a := New(25, -1)
b := New(250, -2) b := New(250, -2)