/* obstack.h - object stack macros Copyright (C) 1988-1994,1996-1999,2003,2004,2005,2009 Free Software Foundation, Inc. This file is part of the GNU C Library. The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. The GNU C Library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with the GNU C Library; if not, see <http://www.gnu.org/licenses/>. */ /* Summary: All the apparent functions defined here are macros. The idea is that you would use these pre-tested macros to solve a very specific set of problems, and they would run fast. Caution: no side-effects in arguments please!! They may be evaluated MANY times!! These macros operate a stack of objects. Each object starts life small, and may grow to maturity. (Consider building a word syllable by syllable.) An object can move while it is growing. Once it has been "finished" it never changes address again. So the "top of the stack" is typically an immature growing object, while the rest of the stack is of mature, fixed size and fixed address objects. These routines grab large chunks of memory, using a function you supply, called `obstack_chunk_alloc'. On occasion, they free chunks, by calling `obstack_chunk_free'. You must define them and declare them before using any obstack macros. Each independent stack is represented by a `struct obstack'. Each of the obstack macros expects a pointer to such a structure as the first argument. One motivation for this package is the problem of growing char strings in symbol tables. Unless you are "fascist pig with a read-only mind" --Gosper's immortal quote from HAKMEM item 154, out of context--you would not like to put any arbitrary upper limit on the length of your symbols. In practice this often means you will build many short symbols and a few long symbols. At the time you are reading a symbol you don't know how long it is. One traditional method is to read a symbol into a buffer, realloc()ating the buffer every time you try to read a symbol that is longer than the buffer. This is beaut, but you still will want to copy the symbol from the buffer to a more permanent symbol-table entry say about half the time. With obstacks, you can work differently. Use one obstack for all symbol names. As you read a symbol, grow the name in the obstack gradually. When the name is complete, finalize it. Then, if the symbol exists already, free the newly read name. The way we do this is to take a large chunk, allocating memory from low addresses. When you want to build a symbol in the chunk you just add chars above the current "high water mark" in the chunk. When you have finished adding chars, because you got to the end of the symbol, you know how long the chars are, and you can create a new object. Mostly the chars will not burst over the highest address of the chunk, because you would typically expect a chunk to be (say) 100 times as long as an average object. In case that isn't clear, when we have enough chars to make up the object, THEY ARE ALREADY CONTIGUOUS IN THE CHUNK (guaranteed) so we just point to it where it lies. No moving of chars is needed and this is the second win: potentially long strings need never be explicitly shuffled. Once an object is formed, it does not change its address during its lifetime. When the chars burst over a chunk boundary, we allocate a larger chunk, and then copy the partly formed object from the end of the old chunk to the beginning of the new larger chunk. We then carry on accrediting characters to the end of the object as we normally would. A special macro is provided to add a single char at a time to a growing object. This allows the use of register variables, which break the ordinary 'growth' macro. Summary: We allocate large chunks. We carve out one object at a time from the current chunk. Once carved, an object never moves. We are free to append data of any size to the currently growing object. Exactly one object is growing in an obstack at any one time. You can run one obstack per control block. You may have as many control blocks as you dare. Because of the way we do it, you can `unwind' an obstack back to a previous state. (You may remove objects much as you would with a stack.) */ /* Don't do the contents of this file more than once. */ #ifndef _OBSTACK_H #define _OBSTACK_H … #ifdef __cplusplus extern "C" { #endif /* We need the type of a pointer subtraction. If __PTRDIFF_TYPE__ is defined, as with GNU C, use that; that way we don't pollute the namespace with <stddef.h>'s symbols. Otherwise, include <stddef.h> and use ptrdiff_t. */ #ifdef __PTRDIFF_TYPE__ #define PTR_INT_TYPE … #else # include <stddef.h> #define PTR_INT_TYPE … #endif /* If B is the base of an object addressed by P, return the result of aligning P to the next multiple of A + 1. B and P must be of type char *. A + 1 must be a power of 2. */ #define __BPTR_ALIGN(B, P, A) … /* Similar to _BPTR_ALIGN (B, P, A), except optimize the common case where pointers can be converted to integers, aligned as integers, and converted back again. If PTR_INT_TYPE is narrower than a pointer (e.g., the AS/400), play it safe and compute the alignment relative to B. Otherwise, use the faster strategy of computing the alignment relative to 0. */ #define __PTR_ALIGN(B, P, A) … #include <string.h> struct _obstack_chunk /* Lives at front of each chunk. */ { … }; struct obstack /* control current object in current chunk */ { … }; /* Declare the external functions we use; they are in obstack.c. */ extern void _obstack_newchunk (struct obstack *, int); extern int _obstack_begin (struct obstack *, int, int, void *(*) (long), void (*) (void *)); extern int _obstack_begin_1 (struct obstack *, int, int, void *(*) (void *, long), void (*) (void *, void *), void *); extern int _obstack_memory_used (struct obstack *); void obstack_free (struct obstack *, void *); /* Error handler called when `obstack_chunk_alloc' failed to allocate more memory. This can be set to a user defined function which should either abort gracefully or use longjump - but shouldn't return. The default action is to print a message and abort. */ extern void (*obstack_alloc_failed_handler) (void); /* Pointer to beginning of object being allocated or to be allocated next. Note that this might not be the final address of the object because a new chunk might be needed to hold the final size. */ #define obstack_base(h) … /* Size for allocating ordinary chunks. */ #define obstack_chunk_size(h) … /* Pointer to next byte not yet allocated in current chunk. */ #define obstack_next_free(h) … /* Mask specifying low bits that should be clear in address of an object. */ #define obstack_alignment_mask(h) … /* To prevent prototype warnings provide complete argument list. */ #define obstack_init(h) … #define obstack_begin(h, size) … #define obstack_specify_allocation(h, size, alignment, chunkfun, freefun) … #define obstack_specify_allocation_with_arg(h, size, alignment, chunkfun, freefun, arg) … #define obstack_chunkfun(h, newchunkfun) … #define obstack_freefun(h, newfreefun) … #define obstack_1grow_fast(h,achar) … #define obstack_blank_fast(h,n) … #define obstack_memory_used(h) … #if defined __GNUC__ && defined __STDC__ && __STDC__ /* NextStep 2.0 cc is really gcc 1.93 but it defines __GNUC__ = 2 and does not implement __extension__. But that compiler doesn't define __GNUC_MINOR__. */ # if __GNUC__ < 2 || (__NeXT__ && !__GNUC_MINOR__) # define __extension__ # endif /* For GNU C, if not -traditional, we can define these macros to compute all args only once without using a global variable. Also, we can avoid using the `temp' slot, to make faster code. */ #define obstack_object_size(OBSTACK) … #define obstack_room(OBSTACK) … #define obstack_make_room(OBSTACK,length) … #define obstack_empty_p(OBSTACK) … #define obstack_grow(OBSTACK,where,length) … #define obstack_grow0(OBSTACK,where,length) … #define obstack_1grow(OBSTACK,datum) … /* These assume that the obstack alignment is good enough for pointers or ints, and that the data added so far to the current object shares that much alignment. */ #define obstack_ptr_grow(OBSTACK,datum) … \ #define obstack_int_grow(OBSTACK,datum) … #define obstack_ptr_grow_fast(OBSTACK,aptr) … #define obstack_int_grow_fast(OBSTACK,aint) … #define obstack_blank(OBSTACK,length) … #define obstack_alloc(OBSTACK,length) … #define obstack_copy(OBSTACK,where,length) … #define obstack_copy0(OBSTACK,where,length) … /* The local variable is named __o1 to avoid a name conflict when obstack_blank is called. */ #define obstack_finish(OBSTACK) … #define obstack_free(OBSTACK, OBJ) … #else /* not __GNUC__ or not __STDC__ */ #define obstack_object_size … #define obstack_room … #define obstack_empty_p … /* Note that the call to _obstack_newchunk is enclosed in (..., 0) so that we can avoid having void expressions in the arms of the conditional expression. Casting the third operand to void was tried before, but some compilers won't accept it. */ #define obstack_make_room … #define obstack_grow … #define obstack_grow0 … #define obstack_1grow … #define obstack_ptr_grow … #define obstack_int_grow … #define obstack_ptr_grow_fast … #define obstack_int_grow_fast … #define obstack_blank … #define obstack_alloc … #define obstack_copy … #define obstack_copy0 … #define obstack_finish … #define obstack_free … #endif /* not __GNUC__ or not __STDC__ */ #ifdef __cplusplus } /* C++ */ #endif #endif /* obstack.h */
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