comparison ffmpeg/libavcodec/rangecoder.c @ 10:6840f77b83aa

commit

+/*
+ * Range coder
+ * Copyright (c) 2004 Michael Niedermayer <[e-mail]>
+ *
+ * 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
+ */
+
+/**
+ * @file
+ * Range coder.
+ * based upon
+ *    "Range encoding: an algorithm for removing redundancy from a digitised
+ *                     message.
+ *     G. N. N. Martin                  Presented in March 1979 to the Video &
+ *                                      Data Recording Conference,
+ *     IBM UK Scientific Center         held in Southampton July 24-27 1979."
+ *
+ */
+
+#include <string.h>
+
+#include "libavutil/avassert.h"
+#include "avcodec.h"
+#include "rangecoder.h"
+#include "bytestream.h"
+
+void ff_init_range_encoder(RangeCoder *c, uint8_t *buf, int buf_size)
+{
+    c->bytestream_start  =
+    c->bytestream        = buf;
+    c->bytestream_end    = buf + buf_size;
+    c->low               = 0;
+    c->range             = 0xFF00;
+    c->outstanding_count = 0;
+    c->outstanding_byte  = -1;
+}
+
+void ff_init_range_decoder(RangeCoder *c, const uint8_t *buf, int buf_size)
+{
+    /* cast to avoid compiler warning */
+    ff_init_range_encoder(c, (uint8_t *)buf, buf_size);
+
+    c->low = bytestream_get_be16((const uint8_t **)&c->bytestream);
+}
+
+void ff_build_rac_states(RangeCoder *c, int factor, int max_p)
+{
+    const int64_t one = 1LL << 32;
+    int64_t p;
+    int last_p8, p8, i;
+
+    memset(c->zero_state, 0, sizeof(c->zero_state));
+    memset(c->one_state, 0, sizeof(c->one_state));
+
+    last_p8 = 0;
+    p       = one / 2;
+    for (i = 0; i < 128; i++) {
+        p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
+        if (p8 <= last_p8)
+            p8 = last_p8 + 1;
+        if (last_p8 && last_p8 < 256 && p8 <= max_p)
+            c->one_state[last_p8] = p8;
+
+        p      += ((one - p) * factor + one / 2) >> 32;
+        last_p8 = p8;
+    }
+
+    for (i = 256 - max_p; i <= max_p; i++) {
+        if (c->one_state[i])
+            continue;
+
+        p  = (i * one + 128) >> 8;
+        p += ((one - p) * factor + one / 2) >> 32;
+        p8 = (256 * p + one / 2) >> 32; // FIXME: try without the one
+        if (p8 <= i)
+            p8 = i + 1;
+        if (p8 > max_p)
+            p8 = max_p;
+        c->one_state[i] = p8;
+    }
+
+    for (i = 1; i < 255; i++)
+        c->zero_state[i] = 256 - c->one_state[256 - i];
+}
+
+/* Return the number of bytes written. */
+int ff_rac_terminate(RangeCoder *c)
+{
+    c->range = 0xFF;
+    c->low  += 0xFF;
+    renorm_encoder(c);
+    c->range = 0xFF;
+    renorm_encoder(c);
+
+    av_assert1(c->low   == 0);
+    av_assert1(c->range >= 0x100);
+
+    return c->bytestream - c->bytestream_start;
+}
+
+#ifdef TEST
+#define SIZE 10240
+
+#include "libavutil/lfg.h"
+#include "libavutil/log.h"
+
+int main(void)
+{
+    RangeCoder c;
+    uint8_t b[9 * SIZE];
+    uint8_t r[9 * SIZE];
+    int i;
+    uint8_t state[10];
+    AVLFG prng;
+
+    av_lfg_init(&prng, 1);
+
+    ff_init_range_encoder(&c, b, SIZE);
+    ff_build_rac_states(&c, 0.05 * (1LL << 32), 128 + 64 + 32 + 16);
+
+    memset(state, 128, sizeof(state));
+
+    for (i = 0; i < SIZE; i++)
+        r[i] = av_lfg_get(&prng) % 7;
+
+    for (i = 0; i < SIZE; i++)
+        put_rac(&c, state, r[i] & 1);
+
+    ff_rac_terminate(&c);
+
+    ff_init_range_decoder(&c, b, SIZE);
+
+    memset(state, 128, sizeof(state));
+
+    for (i = 0; i < SIZE; i++)
+        if ((r[i] & 1) != get_rac(&c, state)) {
+            av_log(NULL, AV_LOG_ERROR, "rac failure at %d\n", i);
+            return 1;
+        }
+
+    return 0;
+}
+#endif /* TEST */