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lib/cc: Define the standard C macro pasting trick in one place.
This file is a workaround for the issue that if you say `a ## b` to create a token that is the name of a macro, the C preprocessor won't expand that macro. So you can't say this: #define FOO__SQUARE(x) ((x)*(x)) #define FOO__CUBE(x) ((x)*(x)*(x)) #define FOO(func, x) FOO__##func(x) Instead, the standard C trick is to add a layer of indirection: #define PASTE(a,b) PASTE__(a,b) #define PASTE__(a,b) a ## b #define FOO__SQUARE(x) ((x)*(x)) #define FOO__CUBE(x) ((x)*(x)*(x)) #define FOO(func, x) PASTE(FOO__, func)(x) We should use this kind of trick sparingly, since it gets confusing.
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noinst_HEADERS += \
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src/lib/cc/compat_compiler.h \
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src/lib/cc/ctassert.h \
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src/lib/cc/tokpaste.h \
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src/lib/cc/torint.h
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src/lib/cc/tokpaste.h
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src/lib/cc/tokpaste.h
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/* Copyright (c) 2001 Matej Pfajfar.
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* Copyright (c) 2001-2004, Roger Dingledine.
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* Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
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* Copyright (c) 2007-2019, The Tor Project, Inc. */
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/* See LICENSE for licensing information */
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/**
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* @file tokpaste.h
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* @brief Token-pasting macros.
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**/
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#ifndef TOR_LIB_CC_TOKPASTE_H
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#define TOR_LIB_CC_TOKPASTE_H
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/**
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* Concatenate `a` and `b` in a way that allows their result itself to be
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* expanded by the preprocessor.
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*
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* Ordinarily you could just say `a ## b` in a macro definition. But doing so
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* results in a symbol which the preprocessor will not then expand. If you
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* wanted to use `a ## b` to create the name of a macro and have the
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* preprocessor expand _that_ macro, you need to have another level of
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* indirection, as this macro provides.
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**/
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#define PASTE(a,b) PASTE__(a,b)
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/** Helper for PASTE(). */
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#define PASTE__(a,b) a ## b
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#endif /* !defined(TOR_LIB_CC_TOKPASTE_H) */
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