recalloc.cpp

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//
// recalloc.cpp
//
//      Copyright (c) Microsoft Corporation. All rights reserved.
//
// Implementation of _recalloc()
//
#include <corecrt_internal.h>
#include <malloc.h>
#include <string.h>
 
 
 
// This function provides the logic for the _recalloc() function.  It is called
// only in the Release CRT (in the Debug CRT, the debug heap has its own
// implementation of _recalloc()).
//
// This function must be marked noinline, otherwise recalloc and
// _recalloc_base will have identical COMDATs, and the linker will fold
// them when calling one from the CRT. This is necessary because recalloc
// needs to support users patching in custom implementations.
extern "C" __declspec(noinline) void* __cdecl _recalloc_base(
    void*  const block,
    size_t const count,
    size_t const size
    )
{
    // Ensure that (count * size) does not overflow
    _VALIDATE_RETURN_NOEXC(count == 0 || (_HEAP_MAXREQ / count) >= size, ENOMEM, nullptr);
 
    size_t const old_block_size = block != nullptr ? _msize_base(block) : 0;
    size_t const new_block_size = count * size;
 
    void* const new_block = _realloc_base(block, new_block_size);
 
    // If the reallocation succeeded and the new block is larger, zero-fill the
    // new bytes:
    if (new_block != nullptr && old_block_size < new_block_size)
    {
        memset(static_cast<char*>(new_block) + old_block_size, 0, new_block_size - old_block_size);
    }
 
    return new_block;
}
 
// Reallocates a block of memory in the heap.
//
// This function reallocates the block pointed to by 'block' such that it is
// 'count * size' bytes in size.  The new size may be either greater or less
// than the original size of the block.  If the new size is greater than the
// original size, the new bytes are zero-filled.  This function shares its
// implementation with the realloc() function; consult the comments of that
// function for more information about the implementation.
//
// This function supports patching and therefore must be marked noinline.
// Both _recalloc_dbg and _recalloc_base must also be marked noinline
// to prevent identical COMDAT folding from substituting calls to _recalloc
// with either other function or vice versa.
extern "C" __declspec(noinline) _CRTRESTRICT void* __cdecl _recalloc(
    void*  const block,
    size_t const count,
    size_t const size
    )
{
    #ifdef _DEBUG
    return _recalloc_dbg(block, count, size, _NORMAL_BLOCK, nullptr, 0);
    #else
    return _recalloc_base(block, count, size);
    #endif
}