118 lines
4.4 KiB
C
118 lines
4.4 KiB
C
/* Variable-sized buffer with on-stack default allocation.
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Copyright (C) 2017-2024 Free Software Foundation, Inc.
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This file is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation; either version 2.1 of the
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License, or (at your option) any later version.
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This file is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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/* Written by Paul Eggert, 2017. */
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#ifndef _GL_SCRATCH_BUFFER_H
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#define _GL_SCRATCH_BUFFER_H
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/* Scratch buffers with a default stack allocation and fallback to
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heap allocation. It is expected that this function is used in this
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way:
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struct scratch_buffer tmpbuf;
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scratch_buffer_init (&tmpbuf);
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while (!function_that_uses_buffer (tmpbuf.data, tmpbuf.length))
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if (!scratch_buffer_grow (&tmpbuf))
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return -1;
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scratch_buffer_free (&tmpbuf);
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return 0;
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The allocation functions (scratch_buffer_grow,
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scratch_buffer_grow_preserve, scratch_buffer_set_array_size) make
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sure that the heap allocation, if any, is freed, so that the code
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above does not have a memory leak. The buffer still remains in a
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state that can be deallocated using scratch_buffer_free, so a loop
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like this is valid as well:
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struct scratch_buffer tmpbuf;
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scratch_buffer_init (&tmpbuf);
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while (!function_that_uses_buffer (tmpbuf.data, tmpbuf.length))
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if (!scratch_buffer_grow (&tmpbuf))
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break;
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scratch_buffer_free (&tmpbuf);
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scratch_buffer_grow and scratch_buffer_grow_preserve are guaranteed
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to grow the buffer by at least 512 bytes. This means that when
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using the scratch buffer as a backing store for a non-character
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array whose element size, in bytes, is 512 or smaller, the scratch
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buffer only has to grow once to make room for at least one more
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element.
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*/
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/* Scratch buffer. Must be initialized with scratch_buffer_init
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before its use. */
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struct scratch_buffer;
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/* Initializes *BUFFER so that BUFFER->data points to BUFFER->__space
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and BUFFER->length reflects the available space. */
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#if 0
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extern void scratch_buffer_init (struct scratch_buffer *buffer);
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#endif
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/* Deallocates *BUFFER (if it was heap-allocated). */
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#if 0
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extern void scratch_buffer_free (struct scratch_buffer *buffer);
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#endif
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/* Grow *BUFFER by some arbitrary amount. The buffer contents is NOT
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preserved. Return true on success, false on allocation failure (in
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which case the old buffer is freed). On success, the new buffer is
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larger than the previous size. On failure, *BUFFER is deallocated,
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but remains in a free-able state, and errno is set. */
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#if 0
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extern bool scratch_buffer_grow (struct scratch_buffer *buffer);
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#endif
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/* Like scratch_buffer_grow, but preserve the old buffer
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contents on success, as a prefix of the new buffer. */
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#if 0
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extern bool scratch_buffer_grow_preserve (struct scratch_buffer *buffer);
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#endif
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/* Grow *BUFFER so that it can store at least NELEM elements of SIZE
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bytes. The buffer contents are NOT preserved. Both NELEM and SIZE
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can be zero. Return true on success, false on allocation failure
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(in which case the old buffer is freed, but *BUFFER remains in a
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free-able state, and errno is set). It is unspecified whether this
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function can reduce the array size. */
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#if 0
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extern bool scratch_buffer_set_array_size (struct scratch_buffer *buffer,
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size_t nelem, size_t size);
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#endif
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/* The implementation is imported from glibc. */
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/* Avoid possible conflicts with symbols exported by the GNU libc. */
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#define __libc_scratch_buffer_grow gl_scratch_buffer_grow
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#define __libc_scratch_buffer_grow_preserve gl_scratch_buffer_grow_preserve
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#define __libc_scratch_buffer_set_array_size gl_scratch_buffer_set_array_size
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#ifndef _GL_LIKELY
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/* Rely on __builtin_expect, as provided by the module 'builtin-expect'. */
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# define _GL_LIKELY(cond) __builtin_expect ((cond), 1)
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# define _GL_UNLIKELY(cond) __builtin_expect ((cond), 0)
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#endif
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#include <malloc/scratch_buffer.gl.h>
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#endif /* _GL_SCRATCH_BUFFER_H */
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