[FFmpeg-devel] [PATCH v2] avutil/buffer: add av_buffer_fast_alloc()

[James Almer]

Same use case as av_fast_malloc(). If the buffer passed to it is
writable and big enough it will be reused, otherwise a new one will
be allocated instead.

Signed-off-by: James Almer <jamrial at gmail.com>
---
TODO: Changelog and APIChanges entries, version bump.

 libavutil/buffer.c | 33 +++++++++++++++++++++++++++++++++
 libavutil/buffer.h | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 75 insertions(+)

diff --git a/libavutil/buffer.c b/libavutil/buffer.c
index 8d1aa5fa84..26e015d7ee 100644
--- a/libavutil/buffer.c
+++ b/libavutil/buffer.c
@@ -215,6 +215,39 @@ int av_buffer_realloc(AVBufferRef **pbuf, int size)
     return 0;
 }
 
+static inline int buffer_fast_alloc(AVBufferRef **pbuf, int size,
+                                    AVBufferRef* (*buffer_alloc)(int size))
+{
+    AVBufferRef *buf = *pbuf;
+
+    if (buf && av_buffer_is_writable(buf)
+            && buf->data == buf->buffer->data
+            && size <= buf->buffer->size) {
+        buf->size = FFMAX(0, size);
+        return 0;
+    }
+
+    av_buffer_unref(pbuf);
+
+    buf = buffer_alloc(size);
+    if (!buf)
+        return AVERROR(ENOMEM);
+
+    *pbuf = buf;
+
+    return 0;
+}
+
+int av_buffer_fast_alloc(AVBufferRef **pbuf, int size)
+{
+    return buffer_fast_alloc(pbuf, size, av_buffer_alloc);
+}
+
+int av_buffer_fast_allocz(AVBufferRef **pbuf, int size)
+{
+    return buffer_fast_alloc(pbuf, size, av_buffer_allocz);
+}
+
 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..1166017d22 100644
--- a/libavutil/buffer.h
+++ b/libavutil/buffer.h
@@ -197,6 +197,48 @@ int av_buffer_make_writable(AVBufferRef **buf);
  */
 int av_buffer_realloc(AVBufferRef **buf, int size);
 
+/**
+ * Allocate a buffer, reusing the given one if writable and large enough.
+ *
+ * @code{.c}
+ * AVBufferRef *buf = ...;
+ * int ret = av_buffer_fast_alloc(&buf, size);
+ * if (ret < 0) {
+ *     // Allocation failed; buf already freed
+ *     return ret;
+ * }
+ * @endcode
+ *
+ * @param buf  A buffer reference. *buf may be NULL. On success, a new buffer
+ *             reference will be written in its place. On failure, it will be
+ *             unreferenced and set to NULL.
+ * @param size Required buffer size.
+ *
+ * @return 0 on success, a negative AVERROR on failure.
+ *
+ * @see av_buffer_realloc()
+ * @see av_buffer_fast_allocz()
+ */
+int av_buffer_fast_alloc(AVBufferRef **buf, int size);
+
+/**
+ * Allocate and clear a buffer, reusing the given one if writable and large
+ * enough.
+ *
+ * Like av_buffer_fast_alloc(), but all newly allocated space is initially
+ * cleared. Reused buffer is not cleared.
+ *
+ * @param buf  A buffer reference. *buf may be NULL. On success, a new buffer
+ *             reference will be written in its place. On failure, it will be
+ *             unreferenced and set to NULL.
+ * @param size Required buffer size.
+ *
+ * @return 0 on success, a negative AVERROR on failure.
+ *
+ * @see av_buffer_fast_alloc()
+ */
+int av_buffer_fast_allocz(AVBufferRef **buf, int size);
+
 /**
  * @}
  */
-- 
2.16.2