80 lines
1.6 KiB
Go
80 lines
1.6 KiB
Go
package fixedn
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import (
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"errors"
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"fmt"
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"math/big"
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"strconv"
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"strings"
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)
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const maxAllowedPrecision = 16
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// ErrInvalidFormat is returned when decimal format is invalid.
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var ErrInvalidFormat = errors.New("invalid decimal format")
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var _pow10 []*big.Int
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func init() {
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var p = int64(1)
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for i := 0; i <= maxAllowedPrecision; i++ {
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_pow10 = append(_pow10, big.NewInt(p))
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p *= 10
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}
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}
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func pow10(n int) *big.Int {
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last := len(_pow10) - 1
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if n <= last {
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return _pow10[n]
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}
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p := new(big.Int)
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p.Mul(_pow10[last], _pow10[1])
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for i := last + 1; i < n; i++ {
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p.Mul(p, _pow10[1])
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}
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return p
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}
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// ToString converts big decimal with specified precision to string.
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func ToString(bi *big.Int, precision int) string {
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var dp, fp big.Int
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dp.QuoRem(bi, pow10(precision), &fp)
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var s = dp.String()
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if fp.Sign() == 0 {
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return s
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}
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frac := fp.Uint64()
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trimmed := 0
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for ; frac%10 == 0; frac /= 10 {
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trimmed++
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}
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return s + "." + fmt.Sprintf("%0"+strconv.FormatUint(uint64(precision-trimmed), 10)+"d", frac)
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}
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// FromString converts string to a big decimal with specified precision.
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func FromString(s string, precision int) (*big.Int, error) {
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parts := strings.SplitN(s, ".", 2)
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bi, ok := new(big.Int).SetString(parts[0], 10)
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if !ok {
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return nil, ErrInvalidFormat
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}
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bi.Mul(bi, pow10(precision))
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if len(parts) == 1 {
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return bi, nil
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}
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if len(parts[1]) > precision {
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return nil, ErrInvalidFormat
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}
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fp, ok := new(big.Int).SetString(parts[1], 10)
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if !ok {
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return nil, ErrInvalidFormat
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}
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fp.Mul(fp, pow10(precision-len(parts[1])))
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if bi.Sign() == -1 {
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return bi.Sub(bi, fp), nil
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}
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return bi.Add(bi, fp), nil
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}
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