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util/Cast: new utility library

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This commit is contained in:
Max Kellermann 2013-12-26 11:42:34 +01:00
parent 617090cfda
commit 0d20130d07
4 changed files with 63 additions and 2 deletions
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1
Makefile.am
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@ -249,6 +249,7 @@ endif
libutil_a_SOURCES = \
src/util/Macros.hxx \
src/util/Cast.hxx \
src/util/Clamp.hxx \
src/util/Error.cxx src/util/Error.hxx \
src/util/Domain.hxx \

3
src/output/HttpdInternal.hxx
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@ -30,6 +30,7 @@
#include "thread/Mutex.hxx"
#include "event/ServerSocket.hxx"
#include "event/DeferredMonitor.hxx"
#include "util/Cast.hxx"
#ifdef _LIBCPP_VERSION
/* can't use incomplete template arguments with libc++ */
@ -157,7 +158,7 @@ public:
#endif
static constexpr HttpdOutput *Cast(audio_output *ao) {
return (HttpdOutput *)((char *)ao - offsetof(HttpdOutput, base));
return ContainerCast(ao, HttpdOutput, base);
}
#if GCC_CHECK_VERSION(4,6) || defined(__clang__)

3
src/tag/TagPool.cxx
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@ -20,6 +20,7 @@
#include "config.h"
#include "TagPool.hxx"
#include "TagItem.hxx"
#include "util/Cast.hxx"
#include <glib.h>
@ -67,7 +68,7 @@ calc_hash(TagType type, const char *p)
static inline struct slot *
tag_item_to_slot(TagItem *item)
{
return (struct slot*)(((char*)item) - offsetof(struct slot, item));
return ContainerCast(item, slot, item);
}
static struct slot *slot_alloc(struct slot *next,

58
src/util/Cast.hxx Normal file
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@ -0,0 +1,58 @@
/*
* Copyright (C) 2013 Max Kellermann <max@duempel.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
* OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef CAST_HXX
#define CAST_HXX
#include <stddef.h>
/**
* Offset the given pointer by the specified number of bytes.
*/
static constexpr void *
OffsetPointer(void *p, ptrdiff_t offset)
{
return (char *)p + offset;
}
template<typename T, typename U>
static constexpr T *
OffsetCast(U *p, ptrdiff_t offset)
{
return reinterpret_cast<T *>(OffsetPointer(p, offset));
}
/**
* Cast the given pointer to a struct member to its parent structure.
*/
#define ContainerCast(p, container, attribute) \
OffsetCast<container, decltype(((container*)nullptr)->attribute)>\
((p), -ptrdiff_t(offsetof(container, attribute)))
#endif