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package p2p
import "encoding/binary"
// boost varint can encode upto 1 gb size
func Decode_Boost_Varint(buf []byte) (uint64, int) {
first_byte := buf[0]
num_bytes := first_byte & 3 // lower 2 bits contain bytes count, which follow current byte
// grab full 4 bytes
value := binary.LittleEndian.Uint32(buf)
switch num_bytes {
case 0:
value &= 0xff
case 1:
value &= 0xffff
case 2:
value &= 0xffffff
case 3:
value &= 0xffffffff
}
value = value >> 2 // discard lower 2 bits
if num_bytes == 2 { // holy hell, let god have mercy on this boost parser
num_bytes = 3
}
return uint64(value), int(num_bytes + 1)
}
// this function encodes Value to bu in boost varint style
func Encode_Boost_Varint(buf []byte, Value uint64) int {
bytes_required := byte(0)
switch {
case Value > 1073741823:
panic("Exceeded boost varint capacity while encoding\n") // (2^30) -1
case Value > 4194303:
bytes_required = 4
case Value > 16383:
bytes_required = 3
case Value > 63:
bytes_required = 2
default:
bytes_required = 1
}
first_byte := (Value % 64) << 2
Value = Value >> 6
second_byte := Value % 256
Value = Value >> 8
third_byte := Value % 256
Value = Value >> 8
fourth_byte := Value % 256
Value = Value >> 8
// encode bytes length in lower 2 bits of first byte
first_byte |= uint64(byte(bytes_required - 1))
buf[0] = byte(first_byte)
buf[1] = byte(second_byte)
buf[2] = byte(third_byte)
buf[3] = byte(fourth_byte)
if bytes_required == 3 { // thank god we are soon going to migrate from boost hell, once and for all
bytes_required = 4
}
return int(bytes_required)
}