Circular buffer fixes

src/rt/circular_buffer.cpp

@@ -4,22 +4,13 @@
 
 #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),
     unit_sz(unit_sz),
-    _buffer_sz(next_power_of_two(
-               INITIAL_CIRCULAR_BUFFFER_SIZE_IN_UNITS * unit_sz)),
+    _buffer_sz(initial_size()),
     _next(0),
     _unread(0),
-    _buffer((uint8_t *)dom->calloc(_buffer_sz)) {
+    _buffer((uint8_t *)dom->malloc(_buffer_sz)) {
 
     A(dom, unit_sz, "Unit size must be larger than zero.");
 
@@ -39,17 +30,38 @@ circular_buffer::~circular_buffer() {
     dom->free(_buffer);
 }
 
+size_t
+circular_buffer::initial_size() {
+    I(dom, unit_sz > 0);
+    return INITIAL_CIRCULAR_BUFFER_SIZE_IN_UNITS * unit_sz;
+}
+
 /**
  * Copies the unread data from this buffer to the "dst" address.
  */
 void
 circular_buffer::transfer(void *dst) {
     I(dom, dst);
-    I(dom, is_power_of_two(_buffer_sz));
+    I(dom, _unread <= _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 - 1)], unit_sz);
+
+    // First copy from _next to either the end of the unread
+    // items or the end of the buffer
+    size_t head_sz;
+    if (_next + _unread <= _buffer_sz) {
+        head_sz = _unread;
+    } else {
+        head_sz = _buffer_sz - _next;
     }
+    I(dom, _next + head_sz <= _buffer_sz);
+    memcpy(ptr, _buffer + _next, head_sz);
+
+    // Then copy any other items from the beginning of the buffer
+    I(dom, _unread >= head_sz);
+    size_t tail_sz = _unread - head_sz;
+    I(dom, head_sz + tail_sz <= _buffer_sz);
+    memcpy(ptr + head_sz, _buffer, tail_sz);
 }
 
 /**
@@ -60,35 +72,37 @@ void
 circular_buffer::enqueue(void *src) {
     I(dom, src);
     I(dom, _unread <= _buffer_sz);
+    I(dom, _buffer);
 
     // Grow if necessary.
     if (_unread == _buffer_sz) {
-        size_t new_buffer_sz = _buffer_sz << 1;
-        I(dom, new_buffer_sz <= MAX_CIRCULAR_BUFFFER_SIZE);
-        void *new_buffer = dom->malloc(new_buffer_sz);
-        transfer(new_buffer);
-        dom->free(_buffer);
-        _buffer = (uint8_t *)new_buffer;
-        _next = 0;
-        _buffer_sz = new_buffer_sz;
+        grow();
     }
 
     dom->log(rust_log::MEM | rust_log::COMM,
              "circular_buffer enqueue "
-             "unread: %d, buffer_sz: %d, unit_sz: %d",
-             _unread, _buffer_sz, unit_sz);
+             "unread: %d, next: %d, buffer_sz: %d, unit_sz: %d",
+             _unread, _next, _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 - 1);
-    memcpy(&_buffer[i], src, unit_sz);
+    size_t dst_idx = _next + _unread;
+    I(dom, dst_idx >= _buffer_sz || dst_idx + unit_sz <= _buffer_sz);
+    if (dst_idx >= _buffer_sz) {
+        dst_idx -= _buffer_sz;
+
+        I(dom, _next >= unit_sz);
+        I(dom, dst_idx <= _next - unit_sz);
+    }
+
+    I(dom, dst_idx + unit_sz <= _buffer_sz);
+    memcpy(&_buffer[dst_idx], src, unit_sz);
     _unread += unit_sz;
 
     dom->log(rust_log::MEM | rust_log::COMM,
-             "circular_buffer pushed data at index: %d", i);
+             "circular_buffer pushed data at index: %d", dst_idx);
 }
 
 /**
@@ -105,34 +119,53 @@ circular_buffer::dequeue(void *dst) {
 
     dom->log(rust_log::MEM | rust_log::COMM,
              "circular_buffer dequeue "
-             "unread: %d, buffer_sz: %d, unit_sz: %d",
-             _unread, _buffer_sz, unit_sz);
+             "unread: %d, next: %d, buffer_sz: %d, unit_sz: %d",
+             _unread, _next, _buffer_sz, unit_sz);
 
+    I(dom, _next + unit_sz <= _buffer_sz);
     if (dst != NULL) {
         memcpy(dst, &_buffer[_next], unit_sz);
     }
     dom->log(rust_log::MEM | rust_log::COMM,
              "shifted data from index %d", _next);
     _unread -= unit_sz;
     _next += unit_sz;
-    I(dom, _next <= _buffer_sz);
     if (_next == _buffer_sz) {
         _next = 0;
     }
 
     // Shrink if possible.
-    if (_buffer_sz >= INITIAL_CIRCULAR_BUFFFER_SIZE_IN_UNITS * unit_sz &&
-        _unread <= _buffer_sz / 4) {
-        dom->log(rust_log::MEM | rust_log::COMM,
-                 "circular_buffer is shrinking to %d bytes", _buffer_sz / 2);
-        void *tmp = dom->malloc(_buffer_sz / 2);
-        transfer(tmp);
-        _buffer_sz >>= 1;
-        dom->free(_buffer);
-        _buffer = (uint8_t *)tmp;
-        _next = 0;
+    if (_buffer_sz > initial_size() && _unread <= _buffer_sz / 4) {
+        shrink();
     }
+}
 
+void
+circular_buffer::grow() {
+    size_t new_buffer_sz = _buffer_sz * 2;
+    I(dom, new_buffer_sz <= MAX_CIRCULAR_BUFFER_SIZE);
+    dom->log(rust_log::MEM | rust_log::COMM,
+             "circular_buffer is growing to %d bytes", new_buffer_sz);
+    void *new_buffer = dom->malloc(new_buffer_sz);
+    transfer(new_buffer);
+    dom->free(_buffer);
+    _buffer = (uint8_t *)new_buffer;
+    _next = 0;
+    _buffer_sz = new_buffer_sz;
+}
+
+void
+circular_buffer::shrink() {
+    size_t new_buffer_sz = _buffer_sz / 2;
+    I(dom, initial_size() <= new_buffer_sz);
+    dom->log(rust_log::MEM | rust_log::COMM,
+             "circular_buffer is shrinking to %d bytes", new_buffer_sz);
+    void *new_buffer = dom->malloc(new_buffer_sz);
+    transfer(new_buffer);
+    dom->free(_buffer);
+    _buffer = (uint8_t *)new_buffer;
+    _next = 0;
+    _buffer_sz = new_buffer_sz;
 }
 
 uint8_t *
@@ -149,3 +182,14 @@ size_t
 circular_buffer::size() {
     return _unread;
 }
+
+//
+// Local Variables:
+// mode: C++
+// fill-column: 78;
+// indent-tabs-mode: nil
+// c-basic-offset: 4
+// buffer-file-coding-system: utf-8-unix
+// compile-command: "make -k -C .. 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
+// End:
+//

src/rt/circular_buffer.h

@@ -7,8 +7,8 @@
 
 class
 circular_buffer : public dom_owned<circular_buffer> {
-    static const size_t INITIAL_CIRCULAR_BUFFFER_SIZE_IN_UNITS = 8;
-    static const size_t MAX_CIRCULAR_BUFFFER_SIZE = 1 << 24;
+    static const size_t INITIAL_CIRCULAR_BUFFER_SIZE_IN_UNITS = 8;
+    static const size_t MAX_CIRCULAR_BUFFER_SIZE = 1 << 24;
 
 public:
     rust_dom *dom;
@@ -24,9 +24,11 @@ circular_buffer : public dom_owned<circular_buffer> {
     size_t size();
 
 private:
-    // Size of the buffer in bytes, should always be a power of two so that
-    // modulo arithmetic (x % _buffer_sz) can optimized away with
-    // (x & (_buffer_sz - 1)).
+    size_t initial_size();
+    void grow();
+    void shrink();
+
+    // Size of the buffer in bytes.
     size_t _buffer_sz;
 
     // Byte offset within the buffer where to read the next unit of data.
@@ -39,4 +41,15 @@ circular_buffer : public dom_owned<circular_buffer> {
     uint8_t *_buffer;
 };
 
+//
+// Local Variables:
+// mode: C++
+// fill-column: 78;
+// indent-tabs-mode: nil
+// c-basic-offset: 4
+// buffer-file-coding-system: utf-8-unix
+// compile-command: "make -k -C .. 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
+// End:
+//
+
 #endif /* CIRCULAR_BUFFER_H */