That's 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). --- gatchat/ringbuffer.c | 14 ++++++++------ 1 files changed, 8 insertions(+), 6 deletions(-) diff --git a/gatchat/ringbuffer.c b/gatchat/ringbuffer.c index becd3f8..27be3a8 100644 --- a/gatchat/ringbuffer.c +++ b/gatchat/ringbuffer.c @@ -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) -- 1.7.1