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gatchat: Optimize ringbuffer modulo operations 

Replace modulo operations in ringbuffer.c by masking operations.  This
is possible because the size of the ring buffers is always a power of
two, and yields a small performance improvement.

The improvement should be mostly visible on processors that implement
division in microcode (Atom) or lack a division instruction (ARM).
This commit is contained in:
Patrick Porlan 2011-03-02 11:15:35 +01:00 committed by Denis Kenzior
parent 9b1675c000
commit 992019cad4
1 changed files with 8 additions and 6 deletions
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14
gatchat/ringbuffer.c
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@ -34,6 +34,7 @@
struct ring_buffer {
unsigned char *buffer;
unsigned int size;
unsigned int mask;
unsigned int in;
unsigned int out;
};
@ -61,6 +62,7 @@ struct ring_buffer *ring_buffer_new(unsigned int size)
}
buffer->size = real_size;
buffer->mask = real_size - 1;
buffer->in = 0;
buffer->out = 0;
@ -78,7 +80,7 @@ int ring_buffer_write(struct ring_buffer *buf, const void *data,
len = MIN(len, buf->size - buf->in + buf->out);
/* Determine how much to write before wrapping */
offset = buf->in % buf->size;
offset = buf->in & buf->mask;
end = MIN(len, buf->size - offset);
memcpy(buf->buffer+offset, d, end);
@ -93,12 +95,12 @@ int ring_buffer_write(struct ring_buffer *buf, const void *data,
unsigned char *ring_buffer_write_ptr(struct ring_buffer *buf,
unsigned int offset)
{
return buf->buffer + (buf->in + offset) % buf->size;
return buf->buffer + ((buf->in + offset) & buf->mask);
}
int ring_buffer_avail_no_wrap(struct ring_buffer *buf)
{
unsigned int offset = buf->in % buf->size;
unsigned int offset = buf->in & buf->mask;
unsigned int len = buf->size - buf->in + buf->out;
return MIN(len, buf->size - offset);
@ -121,7 +123,7 @@ int ring_buffer_read(struct ring_buffer *buf, void *data, unsigned int len)
len = MIN(len, buf->in - buf->out);
/* Grab data from buffer starting at offset until the end */
offset = buf->out % buf->size;
offset = buf->out & buf->mask;
end = MIN(len, buf->size - offset);
memcpy(d, buf->buffer + offset, end);
@ -150,7 +152,7 @@ int ring_buffer_drain(struct ring_buffer *buf, unsigned int len)
int ring_buffer_len_no_wrap(struct ring_buffer *buf)
{
unsigned int offset = buf->out % buf->size;
unsigned int offset = buf->out & buf->mask;
unsigned int len = buf->in - buf->out;
return MIN(len, buf->size - offset);
@ -159,7 +161,7 @@ int ring_buffer_len_no_wrap(struct ring_buffer *buf)
unsigned char *ring_buffer_read_ptr(struct ring_buffer *buf,
unsigned int offset)
{
return buf->buffer + (buf->out + offset) % buf->size;
return buf->buffer + ((buf->out + offset) & buf->mask);
}
int ring_buffer_len(struct ring_buffer *buf)