From 60b0486c11f3c88e0a9aa13986ea338a54468bca Mon Sep 17 00:00:00 2001 From: Michael Bebenita Date: Tue, 27 Jul 2010 23:38:16 -0700 Subject: Make circular buffer use only power-of-two sizes, cheaper arithmetic. --- src/rt/circular_buffer.cpp | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) (limited to 'src/rt/circular_buffer.cpp') diff --git a/src/rt/circular_buffer.cpp b/src/rt/circular_buffer.cpp index 415a966b8fd..ee9cc58e9a7 100644 --- a/src/rt/circular_buffer.cpp +++ b/src/rt/circular_buffer.cpp @@ -4,6 +4,14 @@ #include "rust_internal.h" +bool +is_power_of_two(size_t value) { + if (value > 0) { + return (value & (value - 1)) == 0; + } + return false; +} + circular_buffer::circular_buffer(rust_dom *dom, size_t unit_sz) : dom(dom), _buffer_sz(INITIAL_CIRCULAR_BUFFFER_SIZE_IN_UNITS * unit_sz), @@ -37,9 +45,10 @@ circular_buffer::~circular_buffer() { void circular_buffer::transfer(void *dst) { I(dom, dst); + I(dom, is_power_of_two(_buffer_sz)); uint8_t *ptr = (uint8_t *) dst; for (size_t i = 0; i < _unread; i += _unit_sz) { - memcpy(&ptr[i], &_buffer[(_next + i) % _buffer_sz], _unit_sz); + memcpy(&ptr[i], &_buffer[(_next + i) & (_buffer_sz - 1)], _unit_sz); } } @@ -67,11 +76,12 @@ circular_buffer::enqueue(void *src) { "unread: %d, buffer_sz: %d, unit_sz: %d", _unread, _buffer_sz, _unit_sz); + I(dom, is_power_of_two(_buffer_sz)); I(dom, _unread < _buffer_sz); I(dom, _unread + _unit_sz <= _buffer_sz); // Copy data - size_t i = (_next + _unread) % _buffer_sz; + size_t i = (_next + _unread) & (_buffer_sz - 1); memcpy(&_buffer[i], src, _unit_sz); _unread += _unit_sz; -- cgit 1.4.1-3-g733a5