Class: BinaryCodec::Number

Inherits:
SerializedType show all
Defined in:
lib/binary-codec/types/number.rb

Overview

STNumber, the XRPL "Number" type.

Always 12 bytes: a signed 64 bit mantissa followed by a signed 32 bit exponent, both big endian. Used by the Vault and Lending Protocol fields (AssetsAvailable, DebtTotal, PeriodicPayment and 14 others), which could not be serialised at all before this class existed.

Reference: xrpl.js packages/ripple-binary-codec/src/types/st-number.ts

Constant Summary collapse

BYTE_LENGTH = 
12
MIN_MANTISSA = 
10**18
MAX_MANTISSA = 
10**19 - 1
MAX_INT64 = 
2**63 - 1
MIN_EXPONENT = 
-32_768
MAX_EXPONENT = 
32_768
DEFAULT_VALUE_EXPONENT =

The exponent rippled uses to encode a canonical zero.

-2_147_483_648
RANGE_LOG =

Significant decimal digits rippled renders with.

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NUMBER_PATTERN = 
/\A([-+]?)([0-9]+)(?:\.([0-9]+))?(?:[eE]([+-]?[0-9]+))?\z/

Instance Attribute Summary

Attributes inherited from SerializedType

#bytes

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from SerializedType

from_bytes, from_hex, from_json, get_type_by_name, #to_byte_sink, #to_bytes, #to_hex, #value_of

Constructor Details

#initialize(bytes = nil) ⇒ Number

Returns a new instance of Number.



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# File 'lib/binary-codec/types/number.rb', line 30

def initialize(bytes = nil)
  bytes ||= Array.new(BYTE_LENGTH, 0)

  unless bytes.length == BYTE_LENGTH
    raise StandardError, "Invalid Number length #{bytes.length}"
  end

  super(bytes)
end

Class Method Details

.extract_parts(value) ⇒ Object

Split a number string into an unnormalised mantissa and exponent.

Raises:

  • (StandardError) 


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# File 'lib/binary-codec/types/number.rb', line 108

def self.extract_parts(value)
  match = NUMBER_PATTERN.match(value)
  raise StandardError, "Unable to parse number from string: #{value}" unless match

  sign, int_part, frac_part, exp_part = match.captures

  digits = int_part.sub(/\A0+(?=.)/, '')
  exponent = 0

  unless frac_part.nil? || frac_part.empty?
    digits += frac_part
    exponent -= frac_part.length
  end
  exponent += exp_part.to_i unless exp_part.nil? || exp_part.empty?

  while digits.length > 1 && digits.end_with?('0')
    digits = digits[0..-2]
    exponent += 1
  end

  mantissa = digits.to_i
  mantissa = -mantissa if sign == '-'

  [mantissa, exponent]
end

.from(value) ⇒ Object 



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# File 'lib/binary-codec/types/number.rb', line 40

def self.from(value)
  return value if value.is_a?(Number)
  mantissa, exponent = extract_parts(value.to_s)
  mantissa, exponent = normalize(mantissa, exponent)

  Number.new(pack_signed(mantissa, 8) + pack_signed(exponent, 4))
end

.from_parser(parser, _size_hint = nil) ⇒ Object 



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# File 'lib/binary-codec/types/number.rb', line 48

def self.from_parser(parser, _size_hint = nil)
  Number.new(parser.read(BYTE_LENGTH))
end

.normalize(mantissa, exponent) ⇒ Object

Bring mantissa and exponent into the range rippled expects.

Raises:

  • (StandardError) 


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# File 'lib/binary-codec/types/number.rb', line 135

def self.normalize(mantissa, exponent)
  return [0, DEFAULT_VALUE_EXPONENT] if mantissa.zero?

  negative = mantissa.negative?
  m = mantissa.abs

  while m < MIN_MANTISSA && exponent > MIN_EXPONENT
    exponent -= 1
    m *= 10
  end

  last_digit = nil
  while m > MAX_MANTISSA
    raise StandardError, 'Mantissa and exponent are too large' if exponent >= MAX_EXPONENT

    exponent += 1
    last_digit = m % 10
    m /= 10
  end

  raise StandardError, 'Underflow: value too small to represent' if exponent < MIN_EXPONENT || m < MIN_MANTISSA
  raise StandardError, 'Exponent overflow: value too large to represent' if exponent > MAX_EXPONENT

  if m > MAX_INT64
    raise StandardError, 'Exponent overflow: value too large to represent' if exponent >= MAX_EXPONENT

    exponent += 1
    last_digit = m % 10
    m /= 10
  end

  if last_digit && last_digit >= 5
    m += 1

    if m > MAX_INT64
      raise StandardError, 'Exponent overflow: value too large to represent' if exponent >= MAX_EXPONENT

      last_digit = m % 10
      exponent += 1
      m /= 10
      m += 1 if last_digit >= 5
    end
  end

  [negative ? -m : m, exponent]
end

.pack_signed(value, byte_length) ⇒ Object

Big endian two's complement.



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# File 'lib/binary-codec/types/number.rb', line 183

def self.pack_signed(value, byte_length)
  value += 2**(byte_length * 8) if value.negative?

  Array.new(byte_length) { |i| (value >> (8 * (byte_length - 1 - i))) & 0xFF }
end

.scientific(mantissa, exponent) ⇒ Object

Scientific notation, with trailing zeros moved into the exponent.



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# File 'lib/binary-codec/types/number.rb', line 78

def self.scientific(mantissa, exponent)
  while !mantissa.zero? && (mantissa % 10).zero? && exponent < MAX_EXPONENT
    mantissa /= 10
    exponent += 1
  end

  "#{mantissa}e#{exponent}"
end

.unpack_signed(bytes) ⇒ Object 



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# File 'lib/binary-codec/types/number.rb', line 189

def self.unpack_signed(bytes)
  value = bytes.reduce(0) { |acc, b| (acc << 8) + b }
  boundary = 2**(bytes.length * 8 - 1)

  value >= boundary ? value - 2**(bytes.length * 8) : value
end

Instance Method Details

#positional(mantissa, exponent) ⇒ Object

Plain decimal notation, built by padding the digits out far enough that the decimal point always lands inside the string.



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# File 'lib/binary-codec/types/number.rb', line 93

def positional(mantissa, exponent)
  pad_prefix = RANGE_LOG + 12
  pad_suffix = RANGE_LOG + 8

  raw = ('0' * pad_prefix) + mantissa.to_s + ('0' * pad_suffix)
  offset = exponent + pad_prefix + RANGE_LOG + 1

  integer = raw[0, offset].sub(/\A0+/, '')
  integer = '0' if integer.empty?
  fraction = raw[offset..].sub(/0+\z/, '')

  fraction.empty? ? integer : "#{integer}.#{fraction}"
end

#scientific(mantissa, exponent) ⇒ Object 



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# File 'lib/binary-codec/types/number.rb', line 87

def scientific(mantissa, exponent)
  self.class.scientific(mantissa, exponent)
end

#to_json(_definitions = nil, _field_name = nil) ⇒ Object 



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# File 'lib/binary-codec/types/number.rb', line 52

def to_json(_definitions = nil, _field_name = nil)
  mantissa = self.class.unpack_signed(to_bytes[0, 8])
  exponent = self.class.unpack_signed(to_bytes[8, 4])

  return '0' if mantissa.zero? && exponent == DEFAULT_VALUE_EXPONENT

  negative = mantissa.negative?
  mantissa = mantissa.abs

  # A mantissa above 2^63-1 is shrunk by one digit before serialisation.
  # Restore it so the rendering matches rippled's internal value.
  if !mantissa.zero? && mantissa < MIN_MANTISSA
    mantissa *= 10
    exponent -= 1
  end

  sign = negative ? '-' : ''

  if exponent != 0 && (exponent < -(RANGE_LOG + 10) || exponent > -(RANGE_LOG - 10))
    return sign + scientific(mantissa, exponent)
  end

  sign + positional(mantissa, exponent)
end