Switch grapheme break property searching to Eytzinger binary search (#71668)

stdlib/public/stubs/Unicode/UnicodeGrapheme.cpp

@@ -18,48 +18,40 @@
 #include "swift/shims/UnicodeData.h"
 #include <limits>
 
+
 SWIFT_RUNTIME_STDLIB_INTERNAL
 __swift_uint8_t _swift_stdlib_getGraphemeBreakProperty(__swift_uint32_t scalar) {
 #if !SWIFT_STDLIB_ENABLE_UNICODE_DATA
   swift::swift_abortDisabledUnicodeSupport();
 #else
-  auto low = 0;
-  auto high = GRAPHEME_BREAK_DATA_COUNT - 1;
-
-  while (high >= low) {
-    auto idx = low + (high - low) / 2;
-
-    auto entry = _swift_stdlib_graphemeBreakProperties[idx];
-
+  auto index = 1; //0th element is a dummy element
+  while (index < GRAPHEME_BREAK_DATA_COUNT) {
+    auto entry = _swift_stdlib_graphemeBreakProperties[index];
+    
     // Shift the enum and range count out of the value.
     auto lower = (entry << 11) >> 11;
-
+    
     // Shift the enum out first, then shift out the scalar value.
     auto upper = lower + ((entry << 3) >> 24);
-
+    
     // Shift everything out.
     auto enumValue = (__swift_uint8_t)(entry >> 29);
-
+    
     // Special case: extendedPictographic who used an extra bit for the range.
     if (enumValue == 5) {
       upper = lower + ((entry << 2) >> 23);
     }
-
-    if (scalar >= lower && scalar <= upper) {
-      return enumValue;
-    }
-
-    if (scalar > upper) {
-      low = idx + 1;
-      continue;
-    }
-
+    
+    //If we want the left child of the current node in our virtual tree,
+    //that's at index * 2, if we want the right child it's at (index * 2) + 1
     if (scalar < lower) {
-      high = idx - 1;
-      continue;
+      index = 2 * index;
+    } else if (scalar <= upper) {
+      return enumValue;
+    } else {
+      index = 2 * index + 1;
     }
   }
-
   // If we made it out here, then our scalar was not found in the grapheme
   // array (this occurs when a scalar doesn't map to any grapheme break
   // property). Return the max value here to indicate .any.