InputText: amends: replace IMSTB_TEXTEDIT_GETPREVCHARINDEX code with …

…ImTextFindPreviousUtf8Codepoint(). (7925)

imgui_widgets.cpp

@@ -3955,42 +3955,10 @@ static int IMSTB_TEXTEDIT_GETNEXTCHARINDEX_IMPL(ImGuiInputTextState* obj, int id
     return idx + ImTextCharFromUtf8(&c, obj->TextA.Data + idx, obj->TextA.Data + obj->TextA.Size);
 }
 
-static int CountLeadingHighBits(unsigned char b)
-{
-    for (int i = 0; i < (int)sizeof(b) * 8; i++)
-    {
-        bool set = (b >> (7 - i)) & 1;
-        if (!set)
-            return i;
-    }
-
-    return sizeof(b) * 8;
-}
-
 static int IMSTB_TEXTEDIT_GETPREVCHARINDEX_IMPL(ImGuiInputTextState* obj, int idx)
 {
-    // Backwards check/count for UTF-8 multi byte sequence
-    int num_seq_bytes = 0;
-    for (int i = idx - 1; i >= 0; i -= 1)
-    {
-        bool is_seq_byte = (obj->TextA.Data[i] & 0x80) == 0x80 && (obj->TextA.Data[i] & 0x40) == 0;
-        num_seq_bytes += is_seq_byte;
-        if (!is_seq_byte)
-        {
-            if (num_seq_bytes > 0)
-            {
-                char initial_byte = obj->TextA.Data[i];
-                char num_leading_bits = (char)CountLeadingHighBits(initial_byte);
-                bool is_multi_byte_seq = num_leading_bits == num_seq_bytes + 1;
-                if (is_multi_byte_seq)
-                {
-                    return idx - (num_seq_bytes + 1);
-                }
-            }
-            break;
-        }
-    }
-    return idx - 1;
+    const char* p = ImTextFindPreviousUtf8Codepoint(obj->TextA.Data, obj->TextA.Data + idx);
+    return (int)(p - obj->TextA.Data);
 }
 
 static void STB_TEXTEDIT_DELETECHARS(ImGuiInputTextState* obj, int pos, int n)