refactor: Move inline processor functions and required structs to header file

- Moved DateTimeOffset struct definition to header (required by ColumnBuffers)
- Moved ColumnBuffers struct definition to header (required by inline functions)
- Moved typedef ColumnProcessor, struct ColumnInfoExt, and all 10 inline processor functions to header
- Added new 'INTERNAL: Performance Optimization Helpers' section in header
- Added forward declaration for FetchLobColumnData function
- Enables true cross-compilation-unit inlining for performance optimization
- Follows C++ best practices for inline function placement

Addresses review comments #4, #5, #6 from subrata-ms
Build verified successful (universal2 binary for macOS arm64 + x86_64)

Author: bewithgaurav

mssql_python/pybind/ddbc_bindings.cpp

@@ -135,52 +135,6 @@ struct NumericData {
     }
 };
 
-// Struct to hold the DateTimeOffset structure
-struct DateTimeOffset
-{
-    SQLSMALLINT    year;
-    SQLUSMALLINT   month;
-    SQLUSMALLINT   day;
-    SQLUSMALLINT   hour;
-    SQLUSMALLINT   minute;
-    SQLUSMALLINT   second;
-    SQLUINTEGER    fraction;        // Nanoseconds
-    SQLSMALLINT    timezone_hour;   // Offset hours from UTC
-    SQLSMALLINT    timezone_minute; // Offset minutes from UTC
-};
-
-// Struct to hold data buffers and indicators for each column
-struct ColumnBuffers {
-    std::vector<std::vector<SQLCHAR>> charBuffers;
-    std::vector<std::vector<SQLWCHAR>> wcharBuffers;
-    std::vector<std::vector<SQLINTEGER>> intBuffers;
-    std::vector<std::vector<SQLSMALLINT>> smallIntBuffers;
-    std::vector<std::vector<SQLREAL>> realBuffers;
-    std::vector<std::vector<SQLDOUBLE>> doubleBuffers;
-    std::vector<std::vector<SQL_TIMESTAMP_STRUCT>> timestampBuffers;
-    std::vector<std::vector<SQLBIGINT>> bigIntBuffers;
-    std::vector<std::vector<SQL_DATE_STRUCT>> dateBuffers;
-    std::vector<std::vector<SQL_TIME_STRUCT>> timeBuffers;
-    std::vector<std::vector<SQLGUID>> guidBuffers;
-    std::vector<std::vector<SQLLEN>> indicators;
-    std::vector<std::vector<DateTimeOffset>> datetimeoffsetBuffers;
-
-    ColumnBuffers(SQLSMALLINT numCols, int fetchSize)
-        : charBuffers(numCols),
-          wcharBuffers(numCols),
-          intBuffers(numCols),
-          smallIntBuffers(numCols),
-          realBuffers(numCols),
-          doubleBuffers(numCols),
-          timestampBuffers(numCols),
-          bigIntBuffers(numCols),
-          dateBuffers(numCols),
-          timeBuffers(numCols),
-          guidBuffers(numCols),
-          datetimeoffsetBuffers(numCols),
-          indicators(numCols, std::vector<SQLLEN>(fetchSize)) {}
-};
-
 //-------------------------------------------------------------------------------------------------
 // Function pointer initialization
 //-------------------------------------------------------------------------------------------------
@@ -3185,208 +3139,6 @@ SQLRETURN SQLBindColums(SQLHSTMT hStmt, ColumnBuffers& buffers, py::list& column
     return ret;
 }
 
-// OPTIMIZATION #5: Column processor function type - processes one cell
-// Using function pointers eliminates switch statement overhead in the hot loop
-typedef void (*ColumnProcessor)(PyObject* row, ColumnBuffers& buffers, const void* colInfo, 
-                                 SQLUSMALLINT col, SQLULEN rowIdx, SQLHSTMT hStmt);
-
-// Extended column info struct for processor functions
-struct ColumnInfoExt {
-    SQLSMALLINT dataType;
-    SQLULEN columnSize;
-    SQLULEN processedColumnSize;
-    uint64_t fetchBufferSize;
-    bool isLob;
-};
-
-// Specialized column processors for each data type (eliminates switch in hot loop)
-namespace ColumnProcessors {
-
-inline void ProcessInteger(PyObject* row, ColumnBuffers& buffers, const void*, SQLUSMALLINT col, 
-                           SQLULEN rowIdx, SQLHSTMT) {
-    if (buffers.indicators[col - 1][rowIdx] == SQL_NULL_DATA) {
-        Py_INCREF(Py_None);
-        PyList_SET_ITEM(row, col - 1, Py_None);
-        return;
-    }
-    // OPTIMIZATION #2: Direct Python C API call (bypasses pybind11)
-    PyObject* pyInt = PyLong_FromLong(buffers.intBuffers[col - 1][rowIdx]);
-    PyList_SET_ITEM(row, col - 1, pyInt);
-}
-
-inline void ProcessSmallInt(PyObject* row, ColumnBuffers& buffers, const void*, SQLUSMALLINT col, 
-                            SQLULEN rowIdx, SQLHSTMT) {
-    if (buffers.indicators[col - 1][rowIdx] == SQL_NULL_DATA) {
-        Py_INCREF(Py_None);
-        PyList_SET_ITEM(row, col - 1, Py_None);
-        return;
-    }
-    // OPTIMIZATION #2: Direct Python C API call
-    PyObject* pyInt = PyLong_FromLong(buffers.smallIntBuffers[col - 1][rowIdx]);
-    PyList_SET_ITEM(row, col - 1, pyInt);
-}
-
-inline void ProcessBigInt(PyObject* row, ColumnBuffers& buffers, const void*, SQLUSMALLINT col, 
-                          SQLULEN rowIdx, SQLHSTMT) {
-    if (buffers.indicators[col - 1][rowIdx] == SQL_NULL_DATA) {
-        Py_INCREF(Py_None);
-        PyList_SET_ITEM(row, col - 1, Py_None);
-        return;
-    }
-    // OPTIMIZATION #2: Direct Python C API call
-    PyObject* pyInt = PyLong_FromLongLong(buffers.bigIntBuffers[col - 1][rowIdx]);
-    PyList_SET_ITEM(row, col - 1, pyInt);
-}
-
-inline void ProcessTinyInt(PyObject* row, ColumnBuffers& buffers, const void*, SQLUSMALLINT col, 
-                           SQLULEN rowIdx, SQLHSTMT) {
-    if (buffers.indicators[col - 1][rowIdx] == SQL_NULL_DATA) {
-        Py_INCREF(Py_None);
-        PyList_SET_ITEM(row, col - 1, Py_None);
-        return;
-    }
-    // OPTIMIZATION #2: Direct Python C API call
-    PyObject* pyInt = PyLong_FromLong(buffers.charBuffers[col - 1][rowIdx]);
-    PyList_SET_ITEM(row, col - 1, pyInt);
-}
-
-inline void ProcessBit(PyObject* row, ColumnBuffers& buffers, const void*, SQLUSMALLINT col, 
-                       SQLULEN rowIdx, SQLHSTMT) {
-    if (buffers.indicators[col - 1][rowIdx] == SQL_NULL_DATA) {
-        Py_INCREF(Py_None);
-        PyList_SET_ITEM(row, col - 1, Py_None);
-        return;
-    }
-    // OPTIMIZATION #2: Direct Python C API call
-    PyObject* pyBool = PyBool_FromLong(buffers.charBuffers[col - 1][rowIdx]);
-    PyList_SET_ITEM(row, col - 1, pyBool);
-}
-
-inline void ProcessReal(PyObject* row, ColumnBuffers& buffers, const void*, SQLUSMALLINT col, 
-                        SQLULEN rowIdx, SQLHSTMT) {
-    if (buffers.indicators[col - 1][rowIdx] == SQL_NULL_DATA) {
-        Py_INCREF(Py_None);
-        PyList_SET_ITEM(row, col - 1, Py_None);
-        return;
-    }
-    // OPTIMIZATION #2: Direct Python C API call
-    PyObject* pyFloat = PyFloat_FromDouble(buffers.realBuffers[col - 1][rowIdx]);
-    PyList_SET_ITEM(row, col - 1, pyFloat);
-}
-
-inline void ProcessDouble(PyObject* row, ColumnBuffers& buffers, const void*, SQLUSMALLINT col, 
-                          SQLULEN rowIdx, SQLHSTMT) {
-    if (buffers.indicators[col - 1][rowIdx] == SQL_NULL_DATA) {
-        Py_INCREF(Py_None);
-        PyList_SET_ITEM(row, col - 1, Py_None);
-        return;
-    }
-    // OPTIMIZATION #2: Direct Python C API call
-    PyObject* pyFloat = PyFloat_FromDouble(buffers.doubleBuffers[col - 1][rowIdx]);
-    PyList_SET_ITEM(row, col - 1, pyFloat);
-}
-
-inline void ProcessChar(PyObject* row, ColumnBuffers& buffers, const void* colInfoPtr, 
-                        SQLUSMALLINT col, SQLULEN rowIdx, SQLHSTMT hStmt) {
-    const ColumnInfoExt* colInfo = static_cast<const ColumnInfoExt*>(colInfoPtr);
-    SQLLEN dataLen = buffers.indicators[col - 1][rowIdx];
-    
-    if (dataLen == SQL_NULL_DATA || dataLen == SQL_NO_TOTAL) {
-        Py_INCREF(Py_None);
-        PyList_SET_ITEM(row, col - 1, Py_None);
-        return;
-    }
-    if (dataLen == 0) {
-        PyList_SET_ITEM(row, col - 1, PyUnicode_FromStringAndSize("", 0));
-        return;
-    }
-    
-    uint64_t numCharsInData = dataLen / sizeof(SQLCHAR);
-    // fetchBufferSize includes null-terminator, numCharsInData doesn't. Hence '<'
-    if (!colInfo->isLob && numCharsInData < colInfo->fetchBufferSize) {
-        // OPTIMIZATION #2: Direct Python C API call
-        PyObject* pyStr = PyUnicode_FromStringAndSize(
-            reinterpret_cast<char*>(&buffers.charBuffers[col - 1][rowIdx * colInfo->fetchBufferSize]),
-            numCharsInData);
-        PyList_SET_ITEM(row, col - 1, pyStr);
-    } else {
-        PyList_SET_ITEM(row, col - 1, FetchLobColumnData(hStmt, col, SQL_C_CHAR, false, false).release().ptr());
-    }
-}
-
-inline void ProcessWChar(PyObject* row, ColumnBuffers& buffers, const void* colInfoPtr, 
-                         SQLUSMALLINT col, SQLULEN rowIdx, SQLHSTMT hStmt) {
-    const ColumnInfoExt* colInfo = static_cast<const ColumnInfoExt*>(colInfoPtr);
-    SQLLEN dataLen = buffers.indicators[col - 1][rowIdx];
-    
-    if (dataLen == SQL_NULL_DATA || dataLen == SQL_NO_TOTAL) {
-        Py_INCREF(Py_None);
-        PyList_SET_ITEM(row, col - 1, Py_None);
-        return;
-    }
-    if (dataLen == 0) {
-        PyList_SET_ITEM(row, col - 1, PyUnicode_FromStringAndSize("", 0));
-        return;
-    }
-    
-    uint64_t numCharsInData = dataLen / sizeof(SQLWCHAR);
-    // fetchBufferSize includes null-terminator, numCharsInData doesn't. Hence '<'
-    if (!colInfo->isLob && numCharsInData < colInfo->fetchBufferSize) {
-#if defined(__APPLE__) || defined(__linux__)
-        SQLWCHAR* wcharData = &buffers.wcharBuffers[col - 1][rowIdx * colInfo->fetchBufferSize];
-        // OPTIMIZATION #1: Direct UTF-16 decode
-        PyObject* pyStr = PyUnicode_DecodeUTF16(
-            reinterpret_cast<const char*>(wcharData),
-            numCharsInData * sizeof(SQLWCHAR),
-            NULL,
-            NULL
-        );
-        if (pyStr) {
-            PyList_SET_ITEM(row, col - 1, pyStr);
-        } else {
-            PyErr_Clear();
-            PyList_SET_ITEM(row, col - 1, PyUnicode_FromStringAndSize("", 0));
-        }
-#else
-        // OPTIMIZATION #2: Direct Python C API call
-        PyObject* pyStr = PyUnicode_FromWideChar(
-            reinterpret_cast<wchar_t*>(&buffers.wcharBuffers[col - 1][rowIdx * colInfo->fetchBufferSize]),
-            numCharsInData);
-        PyList_SET_ITEM(row, col - 1, pyStr);
-#endif
-    } else {
-        PyList_SET_ITEM(row, col - 1, FetchLobColumnData(hStmt, col, SQL_C_WCHAR, true, false).release().ptr());
-    }
-}
-
-inline void ProcessBinary(PyObject* row, ColumnBuffers& buffers, const void* colInfoPtr, 
-                          SQLUSMALLINT col, SQLULEN rowIdx, SQLHSTMT hStmt) {
-    const ColumnInfoExt* colInfo = static_cast<const ColumnInfoExt*>(colInfoPtr);
-    SQLLEN dataLen = buffers.indicators[col - 1][rowIdx];
-    
-    if (dataLen == SQL_NULL_DATA || dataLen == SQL_NO_TOTAL) {
-        Py_INCREF(Py_None);
-        PyList_SET_ITEM(row, col - 1, Py_None);
-        return;
-    }
-    if (dataLen == 0) {
-        PyList_SET_ITEM(row, col - 1, PyBytes_FromStringAndSize("", 0));
-        return;
-    }
-    
-    if (!colInfo->isLob && static_cast<size_t>(dataLen) <= colInfo->processedColumnSize) {
-        // OPTIMIZATION #2: Direct Python C API call
-        PyObject* pyBytes = PyBytes_FromStringAndSize(
-            reinterpret_cast<const char*>(&buffers.charBuffers[col - 1][rowIdx * colInfo->processedColumnSize]),
-            dataLen);
-        PyList_SET_ITEM(row, col - 1, pyBytes);
-    } else {
-        PyList_SET_ITEM(row, col - 1, FetchLobColumnData(hStmt, col, SQL_C_BINARY, false, true).release().ptr());
-    }
-}
-
-} // namespace ColumnProcessors
-
 // Fetch rows in batches
 // TODO: Move to anonymous namespace, since it is not used outside this file
 SQLRETURN FetchBatchData(SQLHSTMT hStmt, ColumnBuffers& buffers, py::list& columnNames,