lavu/fifo: Add new AVFifo API based upon the notion of element size

Many AVFifoBuffer users operate on fixed-size elements (e.g. pointers),
but the current FIFO API deals exclusively in bytes, requiring extra
complexity in all these callers.

Add a new AVFifo API creating a FIFO with an element size
that may be larger than a byte. All operations on such a FIFO then
operate on complete elements.

This API does not reuse AVFifoBuffer and its API at all, but instead uses
an opaque struct called AVFifo. The AVFifoBuffer API will be deprecated
in a future commit once all of its users have been switched to the new
API.

Not reusing AVFifoBuffer also allowed to use the full range of size_t
from the beginning.

1 files changed, 226 insertions, 0 deletions

diff --git a/libavutil/fifo.c b/libavutil/fifo.c
index 55621f0dca..0001ccbd43 100644
--- a/libavutil/fifo.c
+++ b/libavutil/fifo.c
@@ -26,6 +26,232 @@
 #include "common.h"
 #include "fifo.h"
 
+struct AVFifo {
+    uint8_t *buffer;
+
+    size_t elem_size, nb_elems;
+    size_t offset_r, offset_w;
+    // distinguishes the ambiguous situation offset_r == offset_w
+    int    is_empty;
+};
+
+AVFifo *av_fifo_alloc2(size_t nb_elems, size_t elem_size,
+                       unsigned int flags)
+{
+    AVFifo *f;
+    void *buffer = NULL;
+
+    if (!elem_size)
+        return NULL;
+
+    if (nb_elems) {
+        buffer = av_realloc_array(NULL, nb_elems, elem_size);
+        if (!buffer)
+            return NULL;
+    }
+    f = av_mallocz(sizeof(*f));
+    if (!f) {
+        av_free(buffer);
+        return NULL;
+    }
+    f->buffer    = buffer;
+    f->nb_elems  = nb_elems;
+    f->elem_size = elem_size;
+    f->is_empty  = 1;
+
+    return f;
+}
+
+size_t av_fifo_elem_size(const AVFifo *f)
+{
+    return f->elem_size;
+}
+
+size_t av_fifo_can_read(const AVFifo *f)
+{
+    if (f->offset_w <= f->offset_r && !f->is_empty)
+        return f->nb_elems - f->offset_r + f->offset_w;
+    return f->offset_w - f->offset_r;
+}
+
+size_t av_fifo_can_write(const AVFifo *f)
+{
+    return f->nb_elems - av_fifo_can_read(f);
+}
+
+int av_fifo_grow2(AVFifo *f, size_t inc)
+{
+    uint8_t *tmp;
+
+    if (inc > SIZE_MAX - f->nb_elems)
+        return AVERROR(EINVAL);
+
+    tmp = av_realloc_array(f->buffer, f->nb_elems + inc, f->elem_size);
+    if (!tmp)
+        return AVERROR(ENOMEM);
+    f->buffer = tmp;
+
+    // move the data from the beginning of the ring buffer
+    // to the newly allocated space
+    if (f->offset_w <= f->offset_r && !f->is_empty) {
+        const size_t copy = FFMIN(inc, f->offset_w);
+        memcpy(tmp + f->nb_elems * f->elem_size, tmp, copy * f->elem_size);
+        if (copy < f->offset_w) {
+            memmove(tmp, tmp + copy * f->elem_size,
+                    (f->offset_w - copy) * f->elem_size);
+            f->offset_w -= copy;
+        } else
+            f->offset_w = f->nb_elems + copy;
+    }
+
+    f->nb_elems += inc;
+
+    return 0;
+}
+
+static int fifo_write_common(AVFifo *f, const uint8_t *buf, size_t *nb_elems,
+                             AVFifoCB read_cb, void *opaque)
+{
+    size_t to_write = *nb_elems;
+    size_t offset_w = f->offset_w;
+    int         ret = 0;
+
+    if (to_write > av_fifo_can_write(f))
+        return AVERROR(ENOSPC);
+
+    while (to_write > 0) {
+        size_t    len = FFMIN(f->nb_elems - offset_w, to_write);
+        uint8_t *wptr = f->buffer + offset_w * f->elem_size;
+
+        if (read_cb) {
+            ret = read_cb(opaque, wptr, &len);
+            if (ret < 0 || len == 0)
+                break;
+        } else {
+            memcpy(wptr, buf, len * f->elem_size);
+            buf += len * f->elem_size;
+        }
+        offset_w += len;
+        if (offset_w >= f->nb_elems)
+            offset_w = 0;
+        to_write -= len;
+    }
+    f->offset_w = offset_w;
+
+    if (*nb_elems != to_write)
+        f->is_empty = 0;
+    *nb_elems -= to_write;
+
+    return ret;
+}
+
+int av_fifo_write(AVFifo *f, const void *buf, size_t nb_elems)
+{
+    return fifo_write_common(f, buf, &nb_elems, NULL, NULL);
+}
+
+int av_fifo_write_from_cb(AVFifo *f, AVFifoCB read_cb,
+                          void *opaque, size_t *nb_elems)
+{
+    return fifo_write_common(f, NULL, nb_elems, read_cb, opaque);
+}
+
+static int fifo_peek_common(const AVFifo *f, uint8_t *buf, size_t *nb_elems,
+                            size_t offset, AVFifoCB write_cb, void *opaque)
+{
+    size_t  to_read = *nb_elems;
+    size_t offset_r = f->offset_r;
+    size_t can_read = av_fifo_can_read(f);
+    int         ret = 0;
+
+    if (offset > can_read || to_read > can_read - offset) {
+        *nb_elems = 0;
+        return AVERROR(EINVAL);
+    }
+
+    if (offset_r >= f->nb_elems - offset)
+        offset_r -= f->nb_elems - offset;
+    else
+        offset_r += offset;
+
+    while (to_read > 0) {
+        size_t    len = FFMIN(f->nb_elems - offset_r, to_read);
+        uint8_t *rptr = f->buffer + offset_r * f->elem_size;
+
+        if (write_cb) {
+            ret = write_cb(opaque, rptr, &len);
+            if (ret < 0 || len == 0)
+                break;
+        } else {
+            memcpy(buf, rptr, len * f->elem_size);
+            buf += len * f->elem_size;
+        }
+        offset_r += len;
+        if (offset_r >= f->nb_elems)
+            offset_r = 0;
+        to_read -= len;
+    }
+
+    *nb_elems -= to_read;
+
+    return ret;
+}
+
+int av_fifo_read(AVFifo *f, void *buf, size_t nb_elems)
+{
+    int ret = fifo_peek_common(f, buf, &nb_elems, 0, NULL, NULL);
+    av_fifo_drain2(f, nb_elems);
+    return ret;
+}
+
+int av_fifo_read_to_cb(AVFifo *f, AVFifoCB write_cb,
+                       void *opaque, size_t *nb_elems)
+{
+    int ret = fifo_peek_common(f, NULL, nb_elems, 0, write_cb, opaque);
+    av_fifo_drain2(f, *nb_elems);
+    return ret;
+}
+
+int av_fifo_peek(AVFifo *f, void *buf, size_t nb_elems, size_t offset)
+{
+    return fifo_peek_common(f, buf, &nb_elems, offset, NULL, NULL);
+}
+
+int av_fifo_peek_to_cb(AVFifo *f, AVFifoCB write_cb, void *opaque,
+                       size_t *nb_elems, size_t offset)
+{
+    return fifo_peek_common(f, NULL, nb_elems, offset, write_cb, opaque);
+}
+
+void av_fifo_drain2(AVFifo *f, size_t size)
+{
+    const size_t cur_size = av_fifo_can_read(f);
+
+    av_assert0(cur_size >= size);
+    if (cur_size == size)
+        f->is_empty = 1;
+
+    if (f->offset_r >= f->nb_elems - size)
+        f->offset_r -= f->nb_elems - size;
+    else
+        f->offset_r += size;
+}
+
+void av_fifo_reset2(AVFifo *f)
+{
+    f->offset_r = f->offset_w = 0;
+    f->is_empty = 1;
+}
+
+void av_fifo_freep2(AVFifo **f)
+{
+    if (*f) {
+        av_freep(&(*f)->buffer);
+        av_freep(f);
+    }
+}
+
+
 #define OLD_FIFO_SIZE_MAX (size_t)FFMIN3(INT_MAX, UINT32_MAX, SIZE_MAX)
 
 AVFifoBuffer *av_fifo_alloc_array(size_t nmemb, size_t size)