Store the first indicator directly into the u16

Since we don't need all bits we can store the first indicator in `u16`
directly and save another 3kb

Author: Markus Westerlind

idna/src/make_uts46_mapping_table.py

@@ -155,12 +155,13 @@ def merge_single_char_ranges(ranges):
 
 print("];\n")
 
-print("static INDEX_TABLE: &'static [(u16, bool)] = &[")
+print("static INDEX_TABLE: &'static [u16] = &[")
 
 offset = 0
 for ranges in optimized_ranges:
     block_len = len(ranges)
-    print("(%s, %s), " % (offset, "true" if block_len == 1 else "false"))
+    single = (1 << 15) if block_len == 1 else 0 
+    print("    %s | %s, " % (offset, single))
     offset += block_len
 
 print("];\n")

idna/src/uts46.rs

@@ -68,11 +68,13 @@ fn find_char(codepoint: char) -> &'static Mapping {
         }
     });
     r.ok().map(|i| {
-        let (offset, single) = INDEX_TABLE[i];
+        let x = INDEX_TABLE[i];
+        let single = (x & (1 << 15)) != 0;
+        let offset = !(1 << 15) & x;
         if single {
             &MAPPING_TABLE[offset as usize]
         } else {
-            &MAPPING_TABLE[(offset + codepoint as u16 - TABLE[i].from as u16) as usize]
+            &MAPPING_TABLE[(offset + (codepoint as u16 - TABLE[i].from as u16)) as usize]
         }
     }).unwrap()
 }