[opt] major speedup by 3x-4x via inlining short functions and caching

Author: fangq

encodevarname.m

@@ -4,7 +4,7 @@
 %
 %    Encode an invalid variable name using a hex-format for bi-directional
 %    conversions.
-
+%
 %    This function is sensitive to the default charset
 %    settings in MATLAB, please call feature('DefaultCharacterSet','utf8')
 %    to set the encoding to UTF-8 before calling this function.
@@ -37,21 +37,39 @@
 %    License: GPLv3 or 3-clause BSD license, see https://github.com/NeuroJSON/easyh5 for details
 %
 
-if (~isvarname(str(1)))
+% Fast path: check first character directly instead of calling isvarname
+c1 = str(1);
+if ~((c1 >= 'a' && c1 <= 'z') || (c1 >= 'A' && c1 <= 'Z'))
+    % First char is not a letter - need to encode it
     if (exist('unicode2native', 'builtin'))
-        str = sprintf('x0x%s_%s', sprintf('%X', unicode2native(str(1))), str(2:end));
+        str = sprintf('x0x%s_%s', sprintf('%X', unicode2native(c1)), str(2:end));
     else
-        str = sprintf('x0x%X_%s', char(str(1)) + 0, str(2:end));
+        str = sprintf('x0x%X_%s', c1 + 0, str(2:end));
     end
 end
-if (isvarname(str))
-    return
+
+% Fast validation: check if all remaining chars are valid (alphanumeric or underscore)
+% This is faster than calling isvarname for simple cases
+len = length(str);
+if len <= 63
+    isvalid = true;
+    for i = 1:len
+        c = str(i);
+        if ~((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c == '_')
+            isvalid = false;
+            break
+        end
+    end
+    if isvalid
+        return
+    end
 end
+
+% Slow path: has invalid characters, need full encoding
 if (exist('unicode2native', 'builtin'))
     str = regexprep(str, '([^0-9A-Za-z_])', '_0x${sprintf(''%X'',unicode2native($1))}_');
 else
     cpos = find(~ismember(str, ['0':'9', 'A':'Z', 'a':'z', '_']));
-    % cpos=regexp(str,'[^0-9A-Za-z_]');
     if (isempty(cpos))
         return
     end