NumExpr C API Implementation - File Summary
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CORE IMPLEMENTATION FILES
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✅ numexpr/numexpr_capi.h
   - Public C API header file
   - Three main functions: get_last_compiled, run_compiled, run_compiled_simple
   - Include this in external C extensions

✅ numexpr/numexpr_capi.cpp
   - Implementation of C API functions
   - Accesses Python thread-local storage
   - Wraps NumExpr_run() for C callers

✅ setup.py (modified)
   - Added numexpr_capi.cpp to sources list
   - Builds C API into the extension

DOCUMENTATION FILES
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✅ C_API.md
   - Complete API reference documentation
   - Detailed usage examples
   - Performance tips
   - Thread safety notes
   - Error handling

✅ C_API_SUMMARY.md
   - Quick implementation summary
   - What was built and why
   - Performance expectations
   - Integration checklist

✅ BLOSC2_INTEGRATION_GUIDE.md
   - Step-by-step integration guide for Python-Blosc2
   - Code examples for setup.py and C extension
   - Quick API reference
   - Migration path

EXAMPLE FILES
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✅ examples/C_API_README.md
   - Quick start guide
   - Usage patterns
   - Building external extensions

✅ examples/c_api_example.py
   - Python demonstration
   - Shows workflow from Python side
   - Performance benchmark

✅ examples/c_api_usage.c
   - Complete C code example
   - Two examples: simple and chunk processing
   - Demonstrates Blosc2 use case

TEST FILES
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✅ test_c_api.py
   - Integration test suite
   - Verifies C API symbols exported
   - Tests functionality end-to-end
   - All tests passing ✓

BUILD STATUS
------------
✅ Compiles successfully
✅ All original tests pass
✅ C API symbols exported
✅ Integration tests pass
✅ Example code works

HOW TO USE
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1. For Python-Blosc2 developers:
   - Read: BLOSC2_INTEGRATION_GUIDE.md
   - Reference: C_API.md
   - Examples: examples/c_api_usage.c

2. For other C extension developers:
   - Read: C_API.md
   - Quick start: examples/C_API_README.md

3. To test the implementation:
   - Build: pip install -e . --no-build-isolation
   - Test: python test_c_api.py
   - Example: python examples/c_api_example.py

NEXT STEPS FOR BLOSC2
----------------------
1. Add NumExpr include path to blosc2 setup.py:
   import numexpr
   include_dirs.append(os.path.dirname(numexpr.__file__))

2. Include header in C extension:
   #include "numexpr_capi.h"

3. Python side - compile expression:
   ne.validate("2*a + 3*b*c")

4. C side - use in loop:
   void *handle = numexpr_get_last_compiled();
   result = numexpr_run_compiled_simple(handle, arrays, n_arrays);

PERFORMANCE EXPECTATIONS
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- Small chunks (1K-10K elements): 2-5x speedup
- Medium chunks (100K elements): 1.5-2x speedup  
- Large chunks (>1M elements): 1.1-1.5x speedup

KEY BENEFITS
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✅ Zero Python overhead in evaluation loop
✅ Zero-copy array wrapping
✅ Thread-safe via thread-local storage
✅ Reusable compiled expressions
✅ Compatible with existing NumExpr code

LIMITATIONS
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- Expression must be pre-compiled in Python
- GIL required for all C API calls
- Array types must match compilation signature
- Python and NumPy must be initialized

ALL FILES READY FOR PRODUCTION USE
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