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/*
* Copyright (c) 2015 Richard Braun.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*
* Circular character buffer.
*/
#ifndef _KERN_CBUF_H
#define _KERN_CBUF_H
/*
* Circular buffer descriptor.
*
* The buffer capacity must be a power-of-two. Indexes are absolute values
* which can overflow. Their difference cannot exceed the capacity.
*/
struct cbuf {
char *buf;
unsigned long capacity;
unsigned long start;
unsigned long end;
};
static inline unsigned long
cbuf_capacity(const struct cbuf *cbuf)
{
return cbuf->capacity;
}
static inline unsigned long
cbuf_start(const struct cbuf *cbuf)
{
return cbuf->start;
}
static inline unsigned long
cbuf_end(const struct cbuf *cbuf)
{
return cbuf->end;
}
static inline unsigned long
cbuf_size(const struct cbuf *cbuf)
{
return cbuf->end - cbuf->start;
}
static inline void
cbuf_clear(struct cbuf *cbuf)
{
cbuf->start = cbuf->end;
}
/*
* Initialize a circular buffer.
*
* The descriptor is set to use the given buffer for storage. Capacity
* must be a power-of-two.
*/
void cbuf_init(struct cbuf *cbuf, char *buf, unsigned long capacity);
/*
* Append a byte to a circular buffer.
*
* The end index is incremented. If the buffer is full, the oldest byte
* is overwritten and the start index is updated accordingly.
*/
void cbuf_push(struct cbuf *cbuf, char byte);
/*
* Read a byte from a circular buffer.
*
* If the buffer is empty, ERROR_AGAIN is returned. Otherwise, the oldest
* byte is stored at the bytep address, the start index is incremented,
* and 0 is returned.
*/
int cbuf_pop(struct cbuf *cbuf, char *bytep);
/*
* Read a byte at a specific location.
*
* If the given index is outside buffer boundaries, ERROR_INVAL is returned.
* Otherwise the byte is stored at the bytep address and 0 is returned.
* The buffer isn't changed by this operation.
*/
int cbuf_read(const struct cbuf *cbuf, unsigned long index, char *bytep);
#endif /* _KERN_CBUF_H */
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