Composing Hangul Syllables

Hangul is the Korean writing system and its primary unit is the syllable. In contrast with other syllabaries like the hiragana and katakana systems used to write Japanese, each syllable can be decomposed into simpler parts that specify the sounds that make up the syllable. Every syllable must have an initial consonant and a vowel; some syllables may contain a final consonant (patchim) or even two final consonants (double patchim).

In a string, each syllable block occupies a single character, but when typing each symbol (jamo) is inputted individually and must be composed into a syllable block. If we think about this composition of symbols to form syllable blocks, it could be very hard to do if the codepoints of the symbols and the syllables were not related. That is, if the codes for ㅁ, 마 and 만 were not related, you'd need a table to know the code of 마 when adding ㅏ to ㅁ, and the code of 만 when typing ㄴ after 마, and so on. The number of combinations would require a relatively large table.

Luckily the Unicode Consortium was smarter than that, and there is an algorithm relating the codes of the jamo and the symbol blocks. It is described here:

Korean language and computers - Wikipedia

The important part is:

The precomposed hangul syllables in the Hangul Syllables block in Unicode are algorithmically defined, using the following formula:

[(initial) × 588 + (medial) × 28 + (final)] + 44032

Initial consonants

Medial vowels

Final consonants

So on this system, ㅁ has value 6 as initial, and ㅏ represents 0 as a vowel. Using the formula, the code for 마 should be 6x588 + 0 + 0 + 44032 = 47560, and that's exactly it. If we want to add ㄴ as a final to 마 to make 만, by the tables and the formula we must add 4 to the code for 마, so 47560 + 4 = 47564 which is the right code for 만. This makes composing syllable blocks when typing much easier.

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