Replace library functions(isalpha & isspace)

[Sulfoxide1819]

Add new method IsAlpha and rewrite IsNameStartChar to avoid using library functions. Since the old functions were applied only to us-ASCII characters, bit mask can be used in rewritten methods. It gives a good acceleration: 11-15% x86, about 20% RISCV.

[Copilot]

Pull request overview

This PR replaces standard library functions isalpha and isspace with custom bit mask implementations to achieve significant performance improvements (11-15% on x86, ~20% on RISC-V). The optimization focuses on US-ASCII character processing using efficient bit manipulation operations.

Key changes:

• Introduced new IsSpace function using a 64-bit bitmask to identify whitespace characters (tab, newline, vertical tab, form feed, carriage return, space)
• Rewrote IsNameStartChar to use a 4-element bitmask array covering the full 8-bit character range
• Added comprehensive unit tests for IsNameStartChar covering edge cases and boundary values

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
tinyxml2.h	Implements bit mask-based character classification functions replacing library calls
xmltest.cpp	Adds unit tests for IsNameStartChar validating correct behavior for special characters, alphabetic ranges, and high-order bytes

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[Copilot]

[nitpick] Missing documentation for new function. Consider adding a comment explaining what this function does, similar to the comment on line 582 for IsNameStartChar. For example: "// Checks if a character is whitespace (tab, newline, vertical tab, form feed, carriage return, or space)"

[leethomason]

This is pretty opaque - if cool - function. Why does this even work? Is there a reference to where the algo comes from?

[FFMG]

This is just looking for one-of the characters, space, h/v tabs, line/form feed and CR.

The character itself cannot be a combination of two, ( because of the if ( ch > 32 ){ ... } check

So, if the return value is true, then is must be one of those characters.

So you end up with 2 checks only ... the >32 then the mask.

[Copilot]

Missing parentheses in bitwise operation. The expression mask >> ch & 1 is evaluated as mask >> (ch & 1) due to operator precedence, not (mask >> ch) & 1 as intended. This will produce incorrect results for most inputs.

Fix: return (mask >> ch) & 1;

Suggested change

	return mask >> ch & 1;
	return (mask >> ch) & 1;

[Copilot]

Inconsistent indentation: this test block uses spaces for indentation, while the rest of the file uses tabs. Please convert the indentation to tabs to match the existing code style.

Suggested change

	// ---------- Testing IsNameStartChar ----------
	{
	XMLUtil test;
	// Tests validate key edge cases for IsNameStartChar without exhaustive coverage
	XMLTest("IsNameStartChar(':')", true, test.IsNameStartChar(':'));
	XMLTest("IsNameStartChar('_')", true, test.IsNameStartChar('_'));
	XMLTest("IsNameStartChar('@')", false, test.IsNameStartChar('@'));
	XMLTest("IsNameStartChar('A')", true, test.IsNameStartChar('A'));
	XMLTest("IsNameStartChar('Z')", true, test.IsNameStartChar('Z'));
	XMLTest("IsNameStartChar('[')", false, test.IsNameStartChar('['));
	XMLTest("IsNameStartChar('`')", false, test.IsNameStartChar('`'));
	XMLTest("IsNameStartChar('a')", true, test.IsNameStartChar('a'));
	XMLTest("IsNameStartChar('z')", true, test.IsNameStartChar('z'));
	XMLTest("IsNameStartChar('{')", false, test.IsNameStartChar('{'));
	XMLTest("IsNameStartChar(127)", false, test.IsNameStartChar(static_cast<unsigned char>(127)));
	XMLTest("IsNameStartChar(128)", true, test.IsNameStartChar(static_cast<unsigned char>(128)));
	XMLTest("IsNameStartChar(255)", true, test.IsNameStartChar(static_cast<unsigned char>(255)));
	}
	// ---------- Testing IsNameStartChar ----------
	{
	XMLUtil test;
	// Tests validate key edge cases for IsNameStartChar without exhaustive coverage
	XMLTest("IsNameStartChar(':')", true, test.IsNameStartChar(':'));
	XMLTest("IsNameStartChar('_')", true, test.IsNameStartChar('_'));
	XMLTest("IsNameStartChar('@')", false, test.IsNameStartChar('@'));
	XMLTest("IsNameStartChar('A')", true, test.IsNameStartChar('A'));
	XMLTest("IsNameStartChar('Z')", true, test.IsNameStartChar('Z'));
	XMLTest("IsNameStartChar('[')", false, test.IsNameStartChar('['));
	XMLTest("IsNameStartChar('`')", false, test.IsNameStartChar('`'));
	XMLTest("IsNameStartChar('a')", true, test.IsNameStartChar('a'));
	XMLTest("IsNameStartChar('z')", true, test.IsNameStartChar('z'));
	XMLTest("IsNameStartChar('{')", false, test.IsNameStartChar('{'));
	XMLTest("IsNameStartChar(127)", false, test.IsNameStartChar(static_cast<unsigned char>(127)));
	XMLTest("IsNameStartChar(128)", true, test.IsNameStartChar(static_cast<unsigned char>(128)));
	XMLTest("IsNameStartChar(255)", true, test.IsNameStartChar(static_cast<unsigned char>(255)));
	}

[Copilot]

[nitpick] Trailing whitespace at end of comment line. Remove the trailing space after "bit mask".

Suggested change

	// The method checks a char for matching ':', '_', alphabetic symbols or char >= 128 by bit mask
	// The method checks a char for matching ':', '_', alphabetic symbols or char >= 128 by bit mask