Floating point discrete cosine transform

Originally committed as revision 21338 to svn://svn.ffmpeg.org/ffmpeg/trunk

1 files changed, 139 insertions, 0 deletions

diff --git a/libavcodec/dct.c b/libavcodec/dct.c
new file mode 100644
index 0000000000..3776349df9
--- /dev/null
+++ b/libavcodec/dct.c
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+/*
+ * (I)DCT Transforms
+ * Copyright (c) 2009 Peter Ross <pross@xvid.org>
+ * Copyright (c) 2010 Alex Converse <alex.converse@gmail.com>
+ * Copyright (c) 2010 Vitor Sessak
+ *
+ * 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 St, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+/**
+ * @file libavcodec/dct.c
+ * (Inverse) Discrete Cosine Transforms. These are also known as the
+ * type II and type III DCTs respectively.
+ */
+
+#include <math.h>
+#include "dsputil.h"
+
+av_cold int ff_dct_init(DCTContext *s, int nbits, int inverse)
+{
+    int n = 1 << nbits;
+    int i;
+
+    s->nbits    = nbits;
+    s->inverse  = inverse;
+
+    ff_init_ff_cos_tabs(nbits+2);
+
+    s->costab = ff_cos_tabs[nbits+2];
+
+    s->csc2 = av_malloc(n/2 * sizeof(FFTSample));
+
+    if (ff_rdft_init(&s->rdft, nbits, inverse) < 0) {
+        av_free(s->csc2);
+        return -1;
+    }
+
+    for (i = 0; i < n/2; i++)
+        s->csc2[i] = 0.5 / sin((M_PI / (2*n) * (2*i + 1)));
+
+    return 0;
+}
+
+/* sin((M_PI * x / (2*n)) */
+#define SIN(s,n,x) (s->costab[(n) - (x)])
+
+/* cos((M_PI * x / (2*n)) */
+#define COS(s,n,x) (s->costab[x])
+
+static void ff_dct_calc_c(DCTContext *ctx, FFTSample *data)
+{
+    int n = 1 << ctx->nbits;
+    int i;
+
+    if (ctx->inverse) {
+        float next = data[n - 1];
+        float inv_n = 1.0f / n;
+
+        for (i = n - 2; i >= 2; i -= 2) {
+            float val1 = data[i    ];
+            float val2 = data[i - 1] - data[i + 1];
+            float c = COS(ctx, n, i);
+            float s = SIN(ctx, n, i);
+
+            data[i    ] = c * val1 + s * val2;
+            data[i + 1] = s * val1 - c * val2;
+        }
+
+        data[1] = 2 * next;
+
+        ff_rdft_calc(&ctx->rdft, data);
+
+        for (i = 0; i < n / 2; i++) {
+            float tmp1 = data[i        ] * inv_n;
+            float tmp2 = data[n - i - 1] * inv_n;
+            float csc = ctx->csc2[i] * (tmp1 - tmp2);
+
+            tmp1 += tmp2;
+            data[i        ] = tmp1 + csc;
+            data[n - i - 1] = tmp1 - csc;
+        }
+    } else {
+        float next;
+        for (i=0; i < n/2; i++) {
+            float tmp1 = data[i        ];
+            float tmp2 = data[n - i - 1];
+            float s = SIN(ctx, n, 2*i + 1);
+
+            s *= tmp1 - tmp2;
+            tmp1 = (tmp1 + tmp2) * 0.5f;
+
+            data[i    ] = tmp1 + s;
+            data[n-i-1] = tmp1 - s;
+        }
+
+        ff_rdft_calc(&ctx->rdft, data);
+
+        next = data[1] * 0.5;
+        data[1] *= -1;
+
+        for (i = n - 2; i >= 0; i -= 2) {
+            float inr = data[i    ];
+            float ini = data[i + 1];
+            float c = COS(ctx, n, i);
+            float s = SIN(ctx, n, i);
+
+            data[i  ] = c * inr + s * ini;
+
+            data[i+1] = next;
+
+            next +=     s * inr - c * ini;
+        }
+    }
+}
+
+void ff_dct_calc(DCTContext *s, FFTSample *data)
+{
+    ff_dct_calc_c(s, data);
+}
+
+av_cold void ff_dct_end(DCTContext *s)
+{
+    ff_rdft_end(&s->rdft);
+    av_free(s->csc2);
+}