Surrogaattiluvut

Surrogaattiluvut, often translated as surrogate numbers or surrogate pairs, are a concept in computing and data representation. They are used to represent characters that cannot be directly encoded using a single unit of a character encoding scheme. This typically occurs when dealing with character sets that contain a vast number of characters, such as the full range of Unicode.

In systems like UTF-16, which uses 16-bit code units, characters outside the Basic Multilingual Plane (BMP) require more than 16 bits. To represent these characters, a surrogate pair is employed. A surrogate pair consists of two 16-bit code units. The first code unit is called a high surrogate, and the second is called a low surrogate. These surrogates are drawn from a specific reserved range within the Unicode character set, indicating that they are not intended to represent characters on their own but rather to combine with another surrogate to form a complete character representation.

The process involves taking a code point beyond the BMP and mapping it to a specific high surrogate and a specific low surrogate. When a system encounters a high surrogate, it expects to find a low surrogate immediately following it to correctly decode the full character. Conversely, encountering a low surrogate without a preceding high surrogate is typically an error. This mechanism allows encodings like UTF-16 to efficiently represent a much larger set of characters than would be possible with fixed 16-bit units alone. Surrogates are a key part of ensuring broad character support, particularly for languages and symbols not included in the initial, more limited character sets.