lavu: add AV_DYNARRAY_ADD() macro.

Signed-off-by: Nicolas George <george@nsup.org>
Reviewed-by: Lukasz Marek <lukasz.m.luki@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/dynarray.h

+/*
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg 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 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg 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 FFmpeg; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVUTIL_DYNARRAY_H
+#define AVUTIL_DYNARRAY_H
+
+#include "log.h"
+#include "mem.h"
+
+/**
+ * Add an element of to a dynamic array.
+ *
+ * The array is reallocated when its number of elements reaches powers of 2.
+ * Therefore, the amortized cost of adding an element is constant.
+ *
+ * In case of success, the pointer to the array is updated in order to
+ * point to the new grown array, and the size is incremented.
+ *
+ * @param av_size_max  maximum size of the array, usually the MAX macro of
+ *                     the type of the size
+ * @param av_elt_size  size of the elements in the array, in bytes
+ * @param av_array     pointer to the array, must be a lvalue
+ * @param av_size      size of the array, must be an interger lvalue
+ * @param av_success   statement to execute on success; at this point, the
+ *                     size variable is not yet incremented
+ * @param av_failure   statement to execute on failure; if this happens, the
+ *                     array and size are not changed; the statement can end
+ *                     with a return or a goto
+ */
+#define AV_DYNARRAY_ADD(av_size_max, av_elt_size, av_array, av_size, \
+                        av_success, av_failure) \
+    do { \
+        size_t av_size_new = (av_size); \
+        if (!((av_size) & ((av_size) - 1))) { \
+            av_size_new = (av_size) ? (av_size) << 1 : 1; \
+            if (av_size_new > (av_size_max) / (av_elt_size)) { \
+                av_size_new = 0; \
+            } else { \
+                void *av_array_new = \
+                    av_realloc((av_array), av_size_new * (av_elt_size)); \
+                av_log(NULL, AV_LOG_DEBUG, "Resizing array to %zd\n", \
+                       av_size_new); \
+                if (!av_array_new) \
+                    av_size_new = 0; \
+                else \
+                    (av_array) = av_array_new; \
+            } \
+        } \
+        if (av_size_new) { \
+            { av_success } \
+            (av_size)++; \
+        } else { \
+            av_failure \
+        } \
+    } while (0)
+
+#endif /* AVUTIL_DYNARRAY_H */