perf(ini): Improve INI parsing performance by using std::from_chars

[Caball009]

This PR replaces 3 cases of sscanf that are used to parse integers and floats from ini files. It's replaced with std::from_chars, which is a C++17 replacement for C functions like sscanf.

std::from_chars can be a good deal faster. I checked the duration of the engine initialization, and it improved by ~2% for debug and release builds.

For convenience I made it so that #define USE_STD_FROM_CHARS_PARSING -1 compares the old and new methods, and throws if there's a difference. I didn't come across a difference for the standard ini files.

[greptile-apps]

Greptile Summary

Replaces three sscanf call-sites in INI parsing with std::from_chars for a claimed ~2% engine-init speedup, with a compile-time #define USE_STD_FROM_CHARS_PARSING -1 validation mode for parity checking. The logic of the new scanType<T> helper is sound, including the documented workaround of using Int64 as the intermediate type to handle "-1" for unsigned scans.

Confidence Score: 5/5

Safe to merge; both open findings are P2 style/portability notes that do not affect correctness on any supported toolchain.

The functional logic is correct and behavior-equivalent to sscanf for all normally-encountered INI values. The two remaining findings are: (1) a non-standard but accidentally-correct __cplusplus constant, and (2) a portability note on float from_chars support that only matters for very old C++17 compilers. Neither is a runtime defect on a modern toolchain.

No files require special attention beyond the two style notes on INI.cpp lines 62 and 1646.

Important Files Changed

Filename	Overview
Core/GameEngine/Source/Common/INI/INI.cpp	Replaces sscanf with std::from_chars for int, unsigned int, and float parsing; uses a non-standard __cplusplus constant (201611L instead of 201703L) and exposes a latent portability risk for float from_chars on older C++17 toolchains.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["INI::scanInt / scanUnsignedInt / scanReal(token)"] --> B{"USE_STD_FROM_CHARS_PARSING == 1?"}
    B -- Yes --> C["scanType<T>(token)\nstd::from_chars → Int64 or Real"]
    C --> D{"ec != std::errc{}?"}
    D -- Error --> E["throw INI_INVALID_DATA"]
    D -- OK --> F["static_cast<T>(result)"]
    B -- No --> G["sscanf(%d/%u/%f)"]
    G --> H{"sscanf result != 1?"}
    H -- Error --> E
    H -- OK --> I["value"]
    I --> J{"USE_STD_FROM_CHARS_PARSING == -1?"}
    J -- Yes --> K["Compare sscanf vs from_chars result"]
    K --> L{"mismatch?"}
    L -- Yes --> E
    L -- No --> M["return value"]
    J -- No --> M
    F --> M

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Prompt To Fix All With AI

This is a comment left during a code review.
Path: Core/GameEngine/Source/Common/INI/INI.cpp
Line: 62

Comment:
**Non-standard `__cplusplus` version constant**

`201611L` is not a defined value of `__cplusplus` for any C++ standard; the value for C++17 is `201703L`. In practice the check still works (no compiler emits `201611L`, so `201703L >= 201611L` is true for C++17 builds), but the magic number is misleading and should use the canonical constant.

```suggestion
#if __cplusplus >= 201703L
```

How can I resolve this? If you propose a fix, please make it concise.

---

This is a comment left during a code review.
Path: Core/GameEngine/Source/Common/INI/INI.cpp
Line: 1646

Comment:
**`std::from_chars` for floats not universally available in C++17 implementations**

The floating-point overloads of `std::from_chars` were added to the C++17 standard but compiler support lagged significantly: GCC added it in 11.1 (2021), Clang in 12.0 (2021), and MSVC in VS 2019 16.4. Any C++17 toolchain older than those thresholds will fail to compile this line because `<charconv>` won't provide a `std::from_chars` overload for `float`. If the project already requires a minimum compiler version that covers these, a comment documenting that requirement here would prevent future confusion.

How can I resolve this? If you propose a fix, please make it concise.

_{Reviews (6): Last reviewed commit: "Simplified macro." | Re-trigger Greptile}

[greptile-apps]

Float != comparison in validation mode may produce false positives

sscanf("%f") and std::from_chars are two independently implemented parsers. For most INI values this is fine, but for decimal strings near a floating-point midpoint (halfway rounding boundary) the two parsers can legitimately round in opposite directions and produce results that differ by 1 ULP — causing the validation mode to throw INI_INVALID_DATA even though both parsed the same string. If this mode is used to validate a full game initialization, those spurious exceptions will hide real data rather than proving parity.

Consider using an epsilon comparison or checking that the two results round-trip to the same string rather than requiring bitwise identity.

Prompt To Fix With AI

This is a comment left during a code review.
Path: Core/GameEngine/Source/Common/INI/INI.cpp
Line: 1706-1708

Comment:
**Float `!=` comparison in validation mode may produce false positives**

`sscanf("%f")` and `std::from_chars` are two independently implemented parsers. For most INI values this is fine, but for decimal strings near a floating-point midpoint (halfway rounding boundary) the two parsers can legitimately round in opposite directions and produce results that differ by 1 ULP — causing the validation mode to throw `INI_INVALID_DATA` even though both parsed the same string. If this mode is used to validate a full game initialization, those spurious exceptions will hide real data rather than proving parity.

Consider using an epsilon comparison or checking that the two results round-trip to the same string rather than requiring bitwise identity.

How can I resolve this? If you propose a fix, please make it concise.

[Caball009]

I realized too late that std::conditional_t<std::is_integral_v<Type>, Int64, Type> result{}; might be slightly better.