[FFmpeg-devel] [PATCH 2/4] avutil/buffer: Add av_fast_malloc equivalent

[Andreas Rheinhardt]

A new function, avpriv_buffer_fast_alloc, is added. Its distinguishing
feature is that the content of the buffer is considered expendable
for the given reference, so that no data copying is performed.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at googlemail.com>
---
 libavutil/buffer.c | 37 +++++++++++++++++++++++++++++++++++++
 libavutil/buffer.h | 19 +++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/libavutil/buffer.c b/libavutil/buffer.c
index 8d1aa5fa84..8303f2fc80 100644
--- a/libavutil/buffer.c
+++ b/libavutil/buffer.c
@@ -215,6 +215,43 @@ int av_buffer_realloc(AVBufferRef **pbuf, int size)
     return 0;
 }
 
+int avpriv_buffer_fast_alloc(AVBufferRef **pbuf, int min_size)
+{
+    AVBufferRef *buf = *pbuf;
+
+    if (!buf || !av_buffer_is_writable(buf)) {
+        av_buffer_unref(pbuf);
+
+        buf = av_buffer_alloc(FFMAX(min_size + (min_size >> 4) + 32,
+                                    min_size));
+        if (!buf)
+            return AVERROR(ENOMEM);
+
+        *pbuf = buf;
+        return 0;
+    }
+
+    if (min_size <= buf->buffer->size) {
+        buf->data = buf->buffer->data;
+        buf->size = buf->buffer->size;
+        return 0;
+    }
+
+    min_size = FFMAX(min_size + (min_size >> 4) + 32, min_size);
+    av_free(buf->buffer->data);
+    buf->buffer->data = av_malloc(min_size);
+    if (!buf->buffer->data) {
+        av_free(buf->buffer);
+        av_freep(pbuf);
+        return AVERROR(ENOMEM);
+    }
+
+    buf->data = buf->buffer->data;
+    buf->size = buf->buffer->size = min_size;
+
+    return 0;
+}
+
 AVBufferPool *av_buffer_pool_init2(int size, void *opaque,
                                    AVBufferRef* (*alloc)(void *opaque, int size),
                                    void (*pool_free)(void *opaque))
diff --git a/libavutil/buffer.h b/libavutil/buffer.h
index 73b6bd0b14..26715275c4 100644
--- a/libavutil/buffer.h
+++ b/libavutil/buffer.h
@@ -197,6 +197,25 @@ int av_buffer_make_writable(AVBufferRef **buf);
  */
 int av_buffer_realloc(AVBufferRef **buf, int size);
 
+/**
+ * Create a writable buffer with given minimum size, reusing the given buffer
+ * if possible. The content of the buffer is considered expendable for the
+ * given reference and might not be preserved at all if the buffer is writable.
+ * The underlying buffer must be compatible with av_free; furthermore, only the
+ * default free callback may be used.
+ *
+ * @param buf      Pointer to NULL or a pointer to a pointer to a buffer reference.
+ *                 On success, **buf will be an AVBufferRef whose size is the
+ *                 allocated size. On failure the reference is unreferenced.
+ *                 If *buf is NULL, a new buffer is allocated.
+ * @param min_size Desired minimal buffer size in bytes.
+ * @return 0 on success, a negative AVERROR on failure.
+ *
+ * @note The function intentionally overallocates in order to reduce the need
+ * for future allocations.
+ */
+int avpriv_buffer_fast_alloc(AVBufferRef **buf, int min_size);
+
 /**
  * @}
  */
-- 
2.19.1