Factor out T_START from match statement

Author: sujayakar

src/normalize.rs

@@ -82,6 +82,10 @@ const L_END: u32 = L_BASE + L_COUNT - 1;
 const V_END: u32 = V_BASE + V_COUNT - 1;
 const T_END: u32 = T_BASE + T_COUNT - 1;
 
+// Composition only occurs for `TPart`s in `U+11A8 ... U+11C2`,
+// i.e. `T_BASE + 1 ... T_END`.
+const T_START: u32 = T_BASE + 1;
+
 pub(crate) fn is_hangul_syllable(c: char) -> bool {
     (c as u32) >= S_BASE && (c as u32) < (S_BASE + S_COUNT)
 }
@@ -127,7 +131,7 @@ fn compose_hangul(a: char, b: char) -> Option<char> {
             Some(unsafe {char::from_u32_unchecked(s)})
         },
         // Compose an LV_Syllable and a trailing consonant into an LVT_Syllable
-        (S_BASE ... S_END, T_BASE ... T_END) if (a - S_BASE) % T_COUNT == 0 && (b - T_BASE) > 0 => {
+        (S_BASE ... S_END, T_START ... T_END) if (a - S_BASE) % T_COUNT == 0 => {
             Some(unsafe {char::from_u32_unchecked(a + (b - T_BASE))})
         },
         _ => None,