diff options
Diffstat (limited to 'obstack.h')
| -rw-r--r-- | obstack.h | 204 |
1 files changed, 0 insertions, 204 deletions
@@ -1,204 +0,0 @@ -/* obstack.h - object stack macros - Copyright (c) 1986 Free Software Foundation, Inc. - -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 "facist 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 aymbol 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 beggining of the new larger chunk. We then carry on -accreting characters to the end of the object as we normaly 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' a obstack - back to a previous state. (You may remove objects much - as you would with a stack.) -*/ - -#ifndef obstackH -#define obstackH - /* these #defines keep it brief */ -#define _Ll struct obstack_chunk -#define _LL (8) /* _L length in chars */ - -struct obstack_chunk /* Lives at front of each chunk. */ -{ - char *obstack_l_limit; /* 1 past end of this chunk */ - _Ll *obstack_l_prev; /* address of prior chunk or NULL */ - char obstack_l_0[4]; /* objects begin here */ -}; - -#if 0 -This function, called like malloc but not returning on failure, -must return a chunk of the size given to it as argument, -aligned on a boundary of 2**OBSTACK_LOG_DEFAULT_ALIGNMENT bytes. - -struct obstack_chunk * obstack_chunk_alloc(); -#endif /* 0 */ - -struct obstack /* control current object in current chunk */ -{ - long chunk_size; /* preferred size to allocate chunks in */ - _Ll* chunk; /* address of current struct obstack_chunk */ - char *object_base; /* address of object we are building */ - char *next_free; /* where to add next char to current object */ - char *chunk_limit; /* address of char after current chunk */ - int temp; /* Temporary for some macros. */ - int alignment_mask; /* Mask of alignment for each object. */ -}; - -/* 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) ((h)->object_base) - -/* Pointer to next byte not yet allocated in current chunk. */ - -#define obstack_next_free(h) ((h)->next_free) - -/* Size of object currently growing */ - -#define obstack_object_size(h) ((h)->next_free - (h)->object_base) - -/* Mask specifying low bits that should be clear in address of an object. */ - -#define obstack_alignment_mask(h) ((h)->alignment_mask) - -#define obstack_init(h) obstack_begin (h, 4096 - 4 - _LL) - -#define obstack_begin(h,try_length) \ -((h)->chunk_size = (try_length) + (_LL), \ - (h)->alignment_mask = ((1 << 2) - 1), \ - _obstack_begin ((h), obstack_chunk_alloc)) - -#define obstack_grow(h,where,length) \ -( (h)->temp = (length), \ - (((h)->next_free + (h)->temp > (h)->chunk_limit) \ - ? _obstack_newchunk ((h), obstack_chunk_alloc, (h)->temp) : 0), \ - bcopy (where, (h)->next_free, (h)->temp), \ - (h)->next_free += (h)->temp) - -#define obstack_grow0(h,where,length) \ -( (h)->temp = (length), \ - (((h)->next_free + (h)->temp + 1 > (h)->chunk_limit) \ - ? _obstack_newchunk ((h), obstack_chunk_alloc, (h)->temp + 1) : 0), \ - bcopy (where, (h)->next_free, (h)->temp), \ - (h)->next_free += (h)->temp, \ - *((h)->next_free)++ = 0) - -#define obstack_1grow(h,datum) \ -( (((h)->next_free + 1 > (h)->chunk_limit) \ - ? _obstack_newchunk ((h), obstack_chunk_alloc, 1) : 0), \ - *((h)->next_free)++ = (datum)) - -#define obstack_blank(h,length) \ -( (h)->temp = (length), \ - (((h)->next_free + (h)->temp > (h)->chunk_limit) \ - ? _obstack_newchunk ((h), obstack_chunk_alloc, (h)->temp) : 0), \ - (h)->next_free += (h)->temp) - -#define obstack_alloc(h,length) \ - (obstack_blank ((h), (length)), obstack_finish (h)) - -#define obstack_copy(h,where,length) \ - (obstack_grow ((h), (where), (length)), obstack_finish (h)) - -#define obstack_copy0(h,where,length) \ - (obstack_grow0 ((h), (where), (length)), obstack_finish (h)) - -#define obstack_room(h) ((long unsigned int) \ - ((h)->chunk_limit - (h)->next_free)) - -#define obstack_1grow_fast(h,achar) (*((h)->next_free)++ = achar) - -#define obstack_blank_fast(h,n) ((h)->next_free += (n)) - -#define obstack_finish(h) \ - ((h)->temp = (int) (h)->object_base, \ - (h)->next_free \ - = (char*)((int)((h)->next_free+(h)->alignment_mask) \ - & ~ ((h)->alignment_mask)), \ - (((h)->next_free - (char *)(h)->chunk \ - > (h)->chunk_limit - (char *)(h)->chunk) \ - ? (h)->next_free = (h)->chunk_limit : 0), \ - (h)->object_base = (h)->next_free, \ - (char *) (h)->temp) - -#define obstack_free(h,obj) \ -(((h)->temp = (char *)(obj) - (char *) (h)->chunk), \ - (((h)->temp >= 0 && (h)->temp < (h)->chunk_limit - (char *) (h)->chunk)\ - ? (int) ((h)->next_free = (h)->object_base \ - = (h)->temp + (char *) (h)->chunk) \ - : (int) _obstack_free ((h), obstack_chunk_free, \ - (h)->temp + (char *) (h)->chunk))) - -#endif /* #ifndef obstackH */ |