Currency Formats

The XRP Ledger has two kinds of money: XRP, and issued currencies. In the XRP Ledger, both types have high precision, although their formats are different.

String Formatting

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XRP Precision

XRP has the same precision as a 64-bit unsigned integer where each unit is equivalent to 0.000001 XRP. Its properties are:

Minimum value: 0
Maximum value: 100000000000 (10¹¹) XRP
- "100000000000000000" (10¹⁷) drops of XRP
Precise to the nearest 0.000001 (10^-6) XRP
- "1" drop of XRP

Issued Currency Precision

Issued currencies in the XRP Ledger are represented with a custom format with the following precision:

Minimum nonzero absolute value: 1000000000000000e-96
Maximum value: 9999999999999999e80
Minimum value: -9999999999999999e80
15 decimal digits of precision

Issued Currency Math

[Source]

Internally, rippled represents numbers for issued currencies in a custom number format. This format can store a wide variety of assets, including those typically measured in very small or very large denominations. Unlike typical floating-point representations of non-whole numbers, this format uses integer math for all calculations, so it always maintains 15 decimal digits of precision. Unlike "arbitrary precision" number formats, the custom format can always be stored in a fixed size of 64 bits.

The internal format consists of four parts: a "not XRP" bit, a sign bit, significant digits, and an exponent. (It uses them in the same way as scientific notation.) They are present in order:

The first (most significant) bit for an issued currency amount is 1 to indicate that it is not an XRP amount. (XRP amounts always have the most significant bit set to 0 to distinguish them from this format.)
The sign bit indicates whether the amount is positive or negative. Unlike standard two's complement integers, 1 indicates positive in the XRP Ledger format, and 0 indicates negative.
The next 8 bits represent the exponent as an unsigned integer. The exponent indicates the scale (what power of 10 the significant digits should be multiplied by) in the range -96 to +80 (inclusive). However, when serializing, we add 97 to the exponent to make it possible to serialize as an unsigned integer. Thus, a serialized value of 1 indicates an exponent of -96, a serialized value of 177 indicates an exponent of 80, and so on.
The remaining 54 bits represent the significant digits as an unsigned integer. When serializing, this value is normalized to the range 10¹⁵ (1000000000000000) to 10¹⁶-1 (9999999999999999) inclusive, except for the special case of the value 0, whose significant digits and sig use the value 0.

Before recording any amount, rippled "canonicalizes" the value so that the significant digits and exponent are within the expected range. For example, the canonical representation of 1 unit of currency is 1000000000000000e-15. The internal calculations generally use integer math so that numbers are always precise within 15 digits. Multiplication and division have adjustments to compensate for over-rounding in the least significant digits.

There is a special case for the value 0. In this case, the sign bit, exponent, and mantissa are all zeroes, so the 64-bit value is serialized as 0x8000000000000000000000000000000000000000.

Currency Codes

All non-XRP currencies in the XRP Ledger have a 160-bit currency code. The rippled APIs map 3-character ASCII strings (case-sensitive) to 160-bit currency codes using a standard mapping. The currency code XRP is disallowed for issued currencies. Currencies with the same code can ripple across connected trustlines. Currency codes have no other behavior built into the XRP Ledger.

Standard Currency Codes

The standard currency mapping allocates the bits as follows:

The first 8 bits must be 0x00.
The next 88 bits are reserved, and should be all 0's.
The next 24 bits represent 3 characters of ASCII. Ripple recommends using ISO 4217 codes, or popular pseudo-ISO 4217 codes such as "BTC". However, any combination of the following characters is permitted: all uppercase and lowercase letters, digits, as well as the symbols ?, !, @, #, $, %, ^, &, *, <, >, (, ), {, }, [, ], and |. The currency code XRP (all-uppercase) is reserved for XRP and cannot be used by issued currencies.
The next 40 bits are reserved and should be all 0's.

Usually, XRP amounts are not specified with currency codes. In the rare case that a field specifies a currency code for XRP, the currency code's binary format is all zeroes.

Nonstandard Currency Codes

You can also issue currency of other types by using a 160-bit (40-character) hexadecimal string such as 015841551A748AD2C1F76FF6ECB0CCCD00000000 as the currency code. To prevent this from being treated as a different currency code type, the first 8 bits MUST NOT be 0x00.

Deprecated: Some previous versions of ripple-lib supported an "interest-bearing" or "demurraging" currency code type. These currencies have the first 8 bits 0x01. Demurraging / interest-bearing currencies are no longer supported, but you may encounter them in ledger data. For more information, see Demurrage.

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