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parserFixPoint.go
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parserFixPoint.go
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package encointer
import (
"fmt"
"math/big"
"strings"
"github.com/huandu/xstrings"
"github.com/shopspring/decimal"
)
// https://github.com/encointer/encointer-js/tree/master/packages/util/src
// Function to produce function to convert fixed-point to Number
//
// Fixed interpretation of u<N> place values
// ... ___ ___ ___ ___ . ___ ___ ___ ___ ...
// ... 8 4 2 1 1/2 1/4 1/8 1/16...
//
// Parameters:
// upper: 0..128 - number of bits in decimal part
// lower: 0..128 - number of bits in fractional part
//
// Produced function parameters:
// raw: substrate_fixed::types::I<upper>F<lower> as I<upper+lower>
// precision: 0..lower number bits in fractional part to process
func ParseI32F32(value decimal.Decimal, precision int) decimal.Decimal {
return parserFixPoint(value, precision, 32, 32)
}
func ParseI16F16(value decimal.Decimal, precision int) decimal.Decimal {
return parserFixPoint(value, precision, 16, 16)
}
func ParseI64F64(value decimal.Decimal, precision int) decimal.Decimal {
return parserFixPoint(value, precision, 64, 64)
}
func assertLength(upper, lower int) (int, error) {
length := upper + lower
if length < 8 || length > 128 {
return 0, fmt.Errorf("bit length can't be less than 8 or bigger than 128, provided %d", length)
}
if length&(length-1) != 0 {
return 0, fmt.Errorf("bit length should be power of 2, provided %d", length)
}
return length, nil
}
func parserFixPoint(value decimal.Decimal, precision int, upper, lower int) decimal.Decimal {
bn := value.BigInt()
length, err := assertLength(upper, lower)
zero := big.NewInt(0)
if err != nil {
return value
}
if len(fmt.Sprintf("%b", bn)) > length {
return value
}
bits := xstrings.RightJustify(fmt.Sprintf("%b", bn), length, "0")
if value.Sign() == -1 {
bits = xstrings.RightJustify(fmt.Sprintf("%b", bn)[1:], length, "0")
}
var lowerBits string
if lower > len(bits) {
lowerBits = xstrings.RightJustify(bits, lower, "0")
} else {
lowerBits = substr(bits, lower, lower-precision)
}
floatPart := big.NewFloat(0)
for k, v := range strings.Split(lowerBits, "") {
if v == "1" {
floatPart.Add(floatPart, big.NewFloat(0).Quo(big.NewFloat(1), big.NewFloat(float64(big.NewInt(0).Exp(big.NewInt(2), big.NewInt(int64(k+1)), big.NewInt(0)).Int64()))))
}
}
floatValue, _ := floatPart.Float64()
upperBits := bits[0 : len(bits)-lower]
decimalPart := zero
if upperBits != "" {
decimalPart, _ = big.NewInt(0).SetString(upperBits, 2)
}
if bn.Cmp(zero) == 1 {
return decimal.NewFromBigInt(decimalPart, 0).Add(decimal.NewFromFloat(floatValue))
}
return decimal.NewFromBigInt(decimalPart, 0).Neg().Sub(decimal.NewFromFloat(floatValue))
}
func substr(input string, length int, endIndex int) string {
asRunes := []rune(input)
if endIndex > 0 {
return string(asRunes[len(asRunes)-length : len(asRunes)-endIndex])
}
return string(asRunes[len(asRunes)-length:])
}