aviralgarg05 opened a new pull request, #18308:
URL: https://github.com/apache/nuttx/pull/18308
## Summary
This PR addresses Issue #18232 by improving the compatibility of
`include/cxx/cmath` with external toolchain libraries.
Users reported compilation errors when using external toolchains (e.g.,
MinGW or ARM GCC with incomplete C library integration) where symbols like
`float_t`, `double_t`, `acosf`, etc., are missing from the global namespace in
the toolchain's `<math.h>`.
The fix modifies `include/cxx/cmath` to verify if the underlying environment
provides these symbols before attempting to import them into the `std`
namespace via `using ::symbol`.
Specifically, it uses a checks: `!defined(CONFIG_ARCH_MATH_H) ||
(defined(FLT_EVAL_METHOD) && FLT_EVAL_METHOD == 0)`.
- If `CONFIG_ARCH_MATH_H` is **not** defined (Standard NuttX build): The
code assumes NuttX's internal `math.h` is used, which provides these symbols,
so usage is enabled.
- If `CONFIG_ARCH_MATH_H` **is** defined (External Toolchain): The code
checks for `FLT_EVAL_METHOD`. If missing (common in broken/deficient headers),
it falls back to defining `float_t`/`double_t` manually and skipping the `using
::function` declarations to prevent compilation errors.
## Impact
- **Users**: Enables compilation of C++ applications using `<cmath>` on
platforms/toolchains where the standard C library headers are incomplete or
non-compliant with C99/C++11.
- **Build**: No impact on standard NuttX builds (`sim:nsh`, etc.) because
`CONFIG_ARCH_MATH_H` is typically undefined, preserving the existing behavior.
- **Compatibility**: Improves portability across diverse toolchains.
## Testing
Verified by reproducing the failure in a simulated environment (fake
toolchain missing `float_t`) and confirming the fix allows compilation.
**Host Machine:** macOS (Apple Silicon)
**Target:** Simulator / Generic
### Before Fix (Log)
Compilation failed with errors indicating missing global symbols:
```
In file included from reproduce_issue.cpp:1:
include/cxx/cmath:47:11: error: no member named 'float_t' in the global
namespace
47 | using ::float_t;
| ~~^
include/cxx/cmath:48:11: error: no member named 'double_t' in the global
namespace
48 | using ::double_t;
| ~~^
include/cxx/cmath:51:11: error: no member named 'acosf' in the global
namespace
51 | using ::acosf;
| ~~^
...
fatal error: too many errors emitted, stopping now [-ferror-limit=]
20 errors generated.
```
### After Fix (Log)
Compilation succeeded with the simulated external toolchain configuration
(`-DCONFIG_ARCH_MATH_H`):
```
(No output - compilation successful)
```
### Regression Testing
Verified that specific standard NuttX builds are unaffected by checking that
`!defined(CONFIG_ARCH_MATH_H)` path remains valid.
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