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3ebf2b4545
If we're going to write a semicolon after calls of relptr_declare(), then we don't need one inside the macro, and removing it suppresses "empty declaration" warnings from pickier compilers (eg pademelon). While at it, we might as well use relptr() inside relptr_declare(), because otherwise that macro would likely go unused altogether. Also improve the comment, which I for one found unclear, and provide a specific example of intended usage.
77 lines
2.6 KiB
C
77 lines
2.6 KiB
C
/*-------------------------------------------------------------------------
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*
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* relptr.h
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* This file contains basic declarations for relative pointers.
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*
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* Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/utils/relptr.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef RELPTR_H
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#define RELPTR_H
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/*
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* Relative pointers are intended to be used when storing an address that may
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* be relative either to the base of the process's address space or some
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* dynamic shared memory segment mapped therein.
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*
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* The idea here is that you declare a relative pointer as relptr(type)
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* and then use relptr_access to dereference it and relptr_store to change
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* it. The use of a union here is a hack, because what's stored in the
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* relptr is always a Size, never an actual pointer. But including a pointer
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* in the union allows us to use stupid macro tricks to provide some measure
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* of type-safety.
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*/
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#define relptr(type) union { type *relptr_type; Size relptr_off; }
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/*
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* pgindent gets confused by declarations that use "relptr(type)" directly,
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* so preferred style is to write
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* typedef struct ... SomeStruct;
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* relptr_declare(SomeStruct, RelptrSomeStruct);
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* and then declare pointer variables as "RelptrSomeStruct someptr".
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*/
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#define relptr_declare(type, relptrtype) \
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typedef relptr(type) relptrtype
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#ifdef HAVE__BUILTIN_TYPES_COMPATIBLE_P
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#define relptr_access(base, rp) \
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(AssertVariableIsOfTypeMacro(base, char *), \
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(__typeof__((rp).relptr_type)) ((rp).relptr_off == 0 ? NULL : \
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(base + (rp).relptr_off)))
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#else
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/*
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* If we don't have __builtin_types_compatible_p, assume we might not have
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* __typeof__ either.
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*/
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#define relptr_access(base, rp) \
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(AssertVariableIsOfTypeMacro(base, char *), \
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(void *) ((rp).relptr_off == 0 ? NULL : (base + (rp).relptr_off)))
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#endif
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#define relptr_is_null(rp) \
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((rp).relptr_off == 0)
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#ifdef HAVE__BUILTIN_TYPES_COMPATIBLE_P
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#define relptr_store(base, rp, val) \
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(AssertVariableIsOfTypeMacro(base, char *), \
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AssertVariableIsOfTypeMacro(val, __typeof__((rp).relptr_type)), \
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(rp).relptr_off = ((val) == NULL ? 0 : ((char *) (val)) - (base)))
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#else
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/*
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* If we don't have __builtin_types_compatible_p, assume we might not have
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* __typeof__ either.
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*/
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#define relptr_store(base, rp, val) \
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(AssertVariableIsOfTypeMacro(base, char *), \
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(rp).relptr_off = ((val) == NULL ? 0 : ((char *) (val)) - (base)))
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#endif
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#define relptr_copy(rp1, rp2) \
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((rp1).relptr_off = (rp2).relptr_off)
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#endif /* RELPTR_H */
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