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/*
* QEMU generic buffers
*
* Copyright (c) 2015 Red Hat, Inc.
*
* This 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 of the License, or (at your option) any later version.
*
* This 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 this library; if not, see <http://www.gnu.org/licenses/>.
*
*/
#include "qemu/buffer.h"
#include "trace.h"
#define BUFFER_MIN_INIT_SIZE 4096
#define BUFFER_MIN_SHRINK_SIZE 65536
/* define the factor alpha for the expentional smoothing
* that is used in the average size calculation. a shift
* of 7 results in an alpha of 1/2^7. */
#define BUFFER_AVG_SIZE_SHIFT 7
static size_t buffer_req_size(Buffer *buffer, size_t len)
{
return MAX(BUFFER_MIN_INIT_SIZE,
pow2ceil(buffer->offset + len));
}
static void buffer_adj_size(Buffer *buffer, size_t len)
{
size_t old = buffer->capacity;
buffer->capacity = buffer_req_size(buffer, len);
buffer->buffer = g_realloc(buffer->buffer, buffer->capacity);
trace_buffer_resize(buffer->name ?: "unnamed",
old, buffer->capacity);
/* make it even harder for the buffer to shrink, reset average size
* to currenty capacity if it is larger than the average. */
buffer->avg_size = MAX(buffer->avg_size,
buffer->capacity << BUFFER_AVG_SIZE_SHIFT);
}
void buffer_init(Buffer *buffer, const char *name, ...)
{
va_list ap;
va_start(ap, name);
buffer->name = g_strdup_vprintf(name, ap);
va_end(ap);
}
static uint64_t buffer_get_avg_size(Buffer *buffer)
{
return buffer->avg_size >> BUFFER_AVG_SIZE_SHIFT;
}
void buffer_shrink(Buffer *buffer)
{
size_t new;
/* Calculate the average size of the buffer as
* avg_size = avg_size * ( 1 - a ) + required_size * a
* where a is 1 / 2 ^ BUFFER_AVG_SIZE_SHIFT. */
buffer->avg_size *= (1 << BUFFER_AVG_SIZE_SHIFT) - 1;
buffer->avg_size >>= BUFFER_AVG_SIZE_SHIFT;
buffer->avg_size += buffer_req_size(buffer, 0);
/* And then only shrink if the average size of the buffer is much
* too big, to avoid bumping up & down the buffers all the time.
* realloc() isn't exactly cheap ... */
new = buffer_req_size(buffer, buffer_get_avg_size(buffer));
if (new < buffer->capacity >> 3 &&
new >= BUFFER_MIN_SHRINK_SIZE) {
buffer_adj_size(buffer, buffer_get_avg_size(buffer));
}
buffer_adj_size(buffer, 0);
}
void buffer_reserve(Buffer *buffer, size_t len)
{
if ((buffer->capacity - buffer->offset) < len) {
buffer_adj_size(buffer, len);
}
}
gboolean buffer_empty(Buffer *buffer)
{
return buffer->offset == 0;
}
uint8_t *buffer_end(Buffer *buffer)
{
return buffer->buffer + buffer->offset;
}
void buffer_reset(Buffer *buffer)
{
buffer->offset = 0;
buffer_shrink(buffer);
}
void buffer_free(Buffer *buffer)
{
trace_buffer_free(buffer->name ?: "unnamed", buffer->capacity);
g_free(buffer->buffer);
g_free(buffer->name);
buffer->offset = 0;
buffer->capacity = 0;
buffer->buffer = NULL;
buffer->name = NULL;
}
void buffer_append(Buffer *buffer, const void *data, size_t len)
{
memcpy(buffer->buffer + buffer->offset, data, len);
buffer->offset += len;
}
void buffer_advance(Buffer *buffer, size_t len)
{
memmove(buffer->buffer, buffer->buffer + len,
(buffer->offset - len));
buffer->offset -= len;
buffer_shrink(buffer);
}
void buffer_move_empty(Buffer *to, Buffer *from)
{
trace_buffer_move_empty(to->name ?: "unnamed",
from->offset,
from->name ?: "unnamed");
assert(to->offset == 0);
g_free(to->buffer);
to->offset = from->offset;
to->capacity = from->capacity;
to->buffer = from->buffer;
from->offset = 0;
from->capacity = 0;
from->buffer = NULL;
}
void buffer_move(Buffer *to, Buffer *from)
{
if (to->offset == 0) {
buffer_move_empty(to, from);
return;
}
trace_buffer_move(to->name ?: "unnamed",
from->offset,
from->name ?: "unnamed");
buffer_reserve(to, from->offset);
buffer_append(to, from->buffer, from->offset);
g_free(from->buffer);
from->offset = 0;
from->capacity = 0;
from->buffer = NULL;
}
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