Function ucdn_decompose 

pub unsafe extern "C" fn ucdn_decompose(
    code: u32,
    a: *mut u32,
    b: *mut u32,
) -> c_int

Pairwise canonical decomposition of a codepoint. This includes
Hangul Jamo decomposition (see chapter 3.12 of the Unicode core
specification).

Hangul is decomposed into L and V jamos for LV forms, and an
LV precomposed syllable and a T jamo for LVT forms.

Arguments

• code Unicode codepoint
• a filled with first codepoint of decomposition
• b filled with second codepoint of decomposition, or 0
  @return success