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Diffstat (limited to 'lib/scratch_buffer.h')
| -rw-r--r-- | lib/scratch_buffer.h | 127 |
1 files changed, 127 insertions, 0 deletions
diff --git a/lib/scratch_buffer.h b/lib/scratch_buffer.h new file mode 100644 index 0000000..f4fe5e8 --- /dev/null +++ b/lib/scratch_buffer.h @@ -0,0 +1,127 @@ +/* Variable-sized buffer with on-stack default allocation. + Copyright (C) 2017-2022 Free Software Foundation, Inc. + + This file 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. + + This file 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 this program. If not, see <https://www.gnu.org/licenses/>. */ + +/* Written by Paul Eggert, 2017. */ + +#ifndef _GL_SCRATCH_BUFFER_H +#define _GL_SCRATCH_BUFFER_H + +/* Scratch buffers with a default stack allocation and fallback to + heap allocation. It is expected that this function is used in this + way: + + struct scratch_buffer tmpbuf; + scratch_buffer_init (&tmpbuf); + + while (!function_that_uses_buffer (tmpbuf.data, tmpbuf.length)) + if (!scratch_buffer_grow (&tmpbuf)) + return -1; + + scratch_buffer_free (&tmpbuf); + return 0; + + The allocation functions (scratch_buffer_grow, + scratch_buffer_grow_preserve, scratch_buffer_set_array_size) make + sure that the heap allocation, if any, is freed, so that the code + above does not have a memory leak. The buffer still remains in a + state that can be deallocated using scratch_buffer_free, so a loop + like this is valid as well: + + struct scratch_buffer tmpbuf; + scratch_buffer_init (&tmpbuf); + + while (!function_that_uses_buffer (tmpbuf.data, tmpbuf.length)) + if (!scratch_buffer_grow (&tmpbuf)) + break; + + scratch_buffer_free (&tmpbuf); + + scratch_buffer_grow and scratch_buffer_grow_preserve are guaranteed + to grow the buffer by at least 512 bytes. This means that when + using the scratch buffer as a backing store for a non-character + array whose element size, in bytes, is 512 or smaller, the scratch + buffer only has to grow once to make room for at least one more + element. +*/ + +/* Scratch buffer. Must be initialized with scratch_buffer_init + before its use. */ +struct scratch_buffer; + +/* Initializes *BUFFER so that BUFFER->data points to BUFFER->__space + and BUFFER->length reflects the available space. */ +#if 0 +extern void scratch_buffer_init (struct scratch_buffer *buffer); +#endif + +/* Deallocates *BUFFER (if it was heap-allocated). */ +#if 0 +extern void scratch_buffer_free (struct scratch_buffer *buffer); +#endif + +/* Grow *BUFFER by some arbitrary amount. The buffer contents is NOT + preserved. Return true on success, false on allocation failure (in + which case the old buffer is freed). On success, the new buffer is + larger than the previous size. On failure, *BUFFER is deallocated, + but remains in a free-able state, and errno is set. */ +#if 0 +extern bool scratch_buffer_grow (struct scratch_buffer *buffer); +#endif + +/* Like scratch_buffer_grow, but preserve the old buffer + contents on success, as a prefix of the new buffer. */ +#if 0 +extern bool scratch_buffer_grow_preserve (struct scratch_buffer *buffer); +#endif + +/* Grow *BUFFER so that it can store at least NELEM elements of SIZE + bytes. The buffer contents are NOT preserved. Both NELEM and SIZE + can be zero. Return true on success, false on allocation failure + (in which case the old buffer is freed, but *BUFFER remains in a + free-able state, and errno is set). It is unspecified whether this + function can reduce the array size. */ +#if 0 +extern bool scratch_buffer_set_array_size (struct scratch_buffer *buffer, + size_t nelem, size_t size); +#endif + +/* Return a copy of *BUFFER's first SIZE bytes as a heap-allocated block, + deallocating *BUFFER if it was heap-allocated. SIZE must be at + most *BUFFER's size. Return NULL (setting errno) on memory + exhaustion. */ +#if 0 +extern void *scratch_buffer_dupfree (struct scratch_buffer *buffer, + size_t size); +#endif + + +/* The implementation is imported from glibc. */ + +/* Avoid possible conflicts with symbols exported by the GNU libc. */ +#define __libc_scratch_buffer_dupfree gl_scratch_buffer_dupfree +#define __libc_scratch_buffer_grow gl_scratch_buffer_grow +#define __libc_scratch_buffer_grow_preserve gl_scratch_buffer_grow_preserve +#define __libc_scratch_buffer_set_array_size gl_scratch_buffer_set_array_size + +#ifndef _GL_LIKELY +/* Rely on __builtin_expect, as provided by the module 'builtin-expect'. */ +# define _GL_LIKELY(cond) __builtin_expect ((cond), 1) +# define _GL_UNLIKELY(cond) __builtin_expect ((cond), 0) +#endif + +#include <malloc/scratch_buffer.gl.h> + +#endif /* _GL_SCRATCH_BUFFER_H */ |