func writeBigInt(value *big.Int, buffer *bytes.Buffer, cutoff *big.Int) (positive bool) {
if value.IsZero() {
buffer.Write(zeroBase)
return !value.RawNeg()
}
if !value.RawNeg() {
positive = true
if value.Cmp(cutoff) == -1 {
encoding := []byte{'\x80', '\x01', '\x01'}
mod := big.NewInt(0)
div, mod := value.DivMod(value, bigint255, mod)
encoding[2] = byte(mod.Int64()) + 1
if div.Sign() == 1 {
div, mod = div.DivMod(div, bigint255, mod)
encoding[1] = byte(mod.Int64()) + 1
if div.Sign() == 1 {
encoding[0] = byte(div.Int64()) + 128
}
}
buffer.Write(encoding)
} else {
value = value.Sub(value, cutoff)
buffer.WriteByte('\xff')
left := big.NewInt(0)
lead, left := value.DivMod(value, bigint255, left)
var n int64 = 1
exp := big.NewInt(0)
div := big.NewInt(0)
for (div.Div(lead, exp.Exp(big.NewInt(253), big.NewInt(n), nil))).Sign() == 1 {
n += 1
}
buffer.WriteByte(byte(n) + 1)
buffer.WriteByte('\xff')
leadChars := make([]byte, 0)
mod := big.NewInt(0)
for {
if lead.IsZero() {
break
}
lead, mod = lead.DivMod(lead, bigint253, mod)
leadChars = append(leadChars, byte(mod.Int64())+2)
}
lenLead := len(leadChars)
if lenLead > 0 {
for i := lenLead - 1; i >= 0; i-- {
buffer.WriteByte(leadChars[i])
}
}
if left.Sign() == 1 {
buffer.WriteByte('\x01')
buffer.WriteByte(byte(left.Int64()))
}
}
} else {
value = value.Neg(value)
if value.Cmp(cutoff) == -1 {
encoding := []byte{'\x7f', '\xfe', '\xfe'}
mod := big.NewInt(0)
div, mod := value.DivMod(value, bigint255, mod)
encoding[2] = 254 - byte(mod.Int64())
if div.Sign() == 1 {
div, mod = div.DivMod(div, bigint255, mod)
encoding[1] = 254 - byte(mod.Int64())
if div.Sign() == 1 {
encoding[0] = 127 - byte(div.Int64())
}
}
buffer.Write(encoding)
} else {
value = value.Sub(value, cutoff)
buffer.WriteByte('\x00')
left := big.NewInt(0)
lead, left := value.DivMod(value, bigint254, left)
var n int64 = 1
exp := big.NewInt(0)
div := big.NewInt(0)
for (div.Div(lead, exp.Exp(big.NewInt(253), big.NewInt(n), nil))).Sign() == 1 {
n += 1
}
buffer.WriteByte(254 - byte(n))
buffer.WriteByte('\x00')
leadChars := make([]byte, 0)
mod := big.NewInt(0)
for {
if lead.IsZero() {
break
}
lead, mod = lead.DivMod(lead, bigint253, mod)
leadChars = append(leadChars, byte(253-mod.Int64()))
}
lenLead := len(leadChars)
if lenLead > 0 {
for i := lenLead - 1; i >= 0; i-- {
buffer.WriteByte(leadChars[i])
}
}
if lenLead > 1 {
buffer.WriteByte('\x00')
}
buffer.WriteByte('\xfe')
if left.Sign() == 1 {
buffer.WriteByte('\x01')
buffer.WriteByte(254 - byte(left.Int64()))
} else {
buffer.WriteByte('\xfe')
}
}
}
return
}
