Tim Starling
93 linhas
2.7 KiB
C++
93 linhas
2.7 KiB
C++
/*
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+----------------------------------------------------------------------+
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| HipHop for PHP |
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+----------------------------------------------------------------------+
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| Copyright (c) 2010-2013 Facebook, Inc. (http://www.facebook.com) |
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+----------------------------------------------------------------------+
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| This source file is subject to version 3.01 of the PHP license, |
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| that is bundled with this package in the file LICENSE, and is |
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| available through the world-wide-web at the following url: |
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| http://www.php.net/license/3_01.txt |
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| If you did not receive a copy of the PHP license and are unable to |
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| obtain it through the world-wide-web, please send a note to |
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| license@php.net so we can mail you a copy immediately. |
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+----------------------------------------------------------------------+
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*/
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#ifndef incl_HPHP_UTIL_COMPACT_SIZED_PTR_H_
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#define incl_HPHP_UTIL_COMPACT_SIZED_PTR_H_
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/*
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* A combined pointer + size intended to save space on x64. The
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* maximum size should be 2^16 anywhere you use this class (although
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* the non-x64 implementation uses a larger size type).
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*
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* For the x64 version, this class relies on the x64 property that a
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* "canonical form" address must have all the upper bits set to the same
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* value as bit 47. Further, it relies on the OS using only "lower
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* half" canonical form addresses for userland pointers. For more,
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* see:
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*
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* http://en.wikipedia.org/wiki/X86-64#Canonical_form_addresses
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*
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* The portable version just uses a pointer plus a uint32_t for the
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* size.
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*/
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namespace HPHP {
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//////////////////////////////////////////////////////////////////////
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#ifdef __x86_64__
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template<class T>
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struct CompactSizedPtr {
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CompactSizedPtr() { set(0, 0); }
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void set(uint32_t size, T* ptr) {
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assert(size <= 0xffffu);
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assert(!(uintptr_t(ptr) >> 48));
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m_data = uintptr_t(ptr) | (size_t(size) << 48);
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}
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uint32_t size() const { return m_data >> 48; }
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const T* ptr() const {
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return const_cast<CompactSizedPtr*>(this)->ptr();
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}
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T* ptr() {
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return reinterpret_cast<T*>(m_data & (-1ull >> 16));
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}
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private:
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uintptr_t m_data;
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};
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#else
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template<class T>
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struct CompactSizedPtr {
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CompactSizedPtr() { set(0, 0); }
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void set(uint32_t size, T* ptr) {
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assert(size <= 0xffffu);
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m_size = size;
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m_ptr = ptr;
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}
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uint32_t size() const { return m_size; }
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const T* ptr() const { return m_ptr; }
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T* ptr() { return m_ptr; }
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private:
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T* m_ptr;
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uint32_t m_size;
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};
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#endif
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//////////////////////////////////////////////////////////////////////
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}
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#endif
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