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+/*

+ * reference discrete cosine transform (double precision)

+ * Copyright (C) 2009 Dylan Yudaken

+ *

+ * 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 libavcodec/dctref.c

+ * reference discrete cosine transform (double precision)

+ *

+ * @author Dylan Yudaken (dyudaken at gmail)

+ *

+ * @note This file could be optimized a lot, but is for

+ * reference and so readability is better.

+ */

+

+#include "libavutil/mathematics.h"

+static double coefficients[8 * 8];

+

+/**

+ * Initialize the double precision discrete cosine transform

+ * functions fdct & idct.

+ */

+av_cold void ff_ref_dct_init(void)

+{

+    unsigned int i, j;

+

+    for (j = 0; j < 8; ++j) {

+        coefficients[j] = sqrt(0.125);

+        for (i = 8; i < 64; i += 8) {

+            coefficients[i + j] = 0.5 * cos(i * (j + 0.5) * M_PI / 64.0);

+        }

+    }

+}

+

+/**

+ * Transform 8x8 block of data with a double precision forward DCT <br>

+ * This is a reference implementation.

+ *

+ * @param block pointer to 8x8 block of data to transform

+ */

+void ff_ref_fdct(short *block)

+{

+    /* implement the equation: block = coefficients * block * coefficients' */

+

+    unsigned int i, j, k;

+    double out[8 * 8];

+

+    /* out = coefficients * block */

+    for (i = 0; i < 64; i += 8) {

+        for (j = 0; j < 8; ++j) {

+            double tmp = 0;

+            for (k = 0; k < 8; ++k) {

+                tmp += coefficients[i + k] * block[k * 8 + j];

+            }

+            out[i + j] = tmp * 8;

+        }

+    }

+

+    /* block = out * (coefficients') */

+    for (j = 0; j < 8; ++j) {

+        for (i = 0; i < 64; i += 8) {

+            double tmp = 0;

+            for (k = 0; k < 8; ++k) {

+                tmp += out[i + k] * coefficients[j * 8 + k];

+            }

+            block[i + j] = floor(tmp + 0.499999999999);

+        }

+    }

+}

+

+/**

+ * Transform 8x8 block of data with a double precision inverse DCT <br>

+ * This is a reference implementation.

+ *

+ * @param block pointer to 8x8 block of data to transform

+ */

+void ff_ref_idct(short *block)

+{

+    /* implement the equation: block = (coefficients') * block * coefficients */

+

+    unsigned int i, j, k;

+    double out[8 * 8];

+

+    /* out = block * coefficients */

+    for (i = 0; i < 64; i += 8) {

+        for (j = 0; j < 8; ++j) {

+            double tmp = 0;

+            for (k = 0; k < 8; ++k) {

+                tmp += block[i + k] * coefficients[k * 8 + j];

+            }

+            out[i + j] = tmp;

+        }

+    }

+

+    /* block = (coefficients') * out */

+    for (i = 0; i < 8; ++i) {

+        for (j = 0; j < 8; ++j) {

+            double tmp = 0;

+            for (k = 0; k < 64; k += 8) {

+                tmp += coefficients[k + i] * out[k + j];

+            }

+            block[i * 8 + j] = floor(tmp + 0.5);

+        }

+    }

+}