From 686025404486c751c808aa7441da19cacef637b4 Mon Sep 17 00:00:00 2001
From: Alex Converse <alex.converse@gmail.com>
Date: Fri, 30 Jan 2009 20:15:48 +0000
Subject: Add the rdft family of transforms (fft/ifft of an all real sequence)
 to dsputil.

Originally committed as revision 16864 to svn://svn.ffmpeg.org/ffmpeg/trunk
---
 libavcodec/rdft.c | 127 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 libavcodec/rdft.c

(limited to 'libavcodec/rdft.c')

diff --git a/libavcodec/rdft.c b/libavcodec/rdft.c
new file mode 100644
index 0000000000..36c6f1bf05
--- /dev/null
+++ b/libavcodec/rdft.c
@@ -0,0 +1,127 @@
+/*
+ * (I)RDFT transforms
+ * Copyright (c) 2009 Alex Converse <alex dot converse at gmail dot com>
+ *
+ * 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
+ */
+#include <math.h>
+#include "dsputil.h"
+
+/**
+ * @file rdft.c
+ * (Inverse) Real Discrete Fourier Transforms.
+ */
+
+/* sin(2*pi*x/n) for 0<=x<n/4, followed by n/2<=x<3n/4 */
+DECLARE_ALIGNED_16(FFTSample, ff_sin_16[8]);
+DECLARE_ALIGNED_16(FFTSample, ff_sin_32[16]);
+DECLARE_ALIGNED_16(FFTSample, ff_sin_64[32]);
+DECLARE_ALIGNED_16(FFTSample, ff_sin_128[64]);
+DECLARE_ALIGNED_16(FFTSample, ff_sin_256[128]);
+DECLARE_ALIGNED_16(FFTSample, ff_sin_512[256]);
+DECLARE_ALIGNED_16(FFTSample, ff_sin_1024[512]);
+DECLARE_ALIGNED_16(FFTSample, ff_sin_2048[1024]);
+DECLARE_ALIGNED_16(FFTSample, ff_sin_4096[2048]);
+DECLARE_ALIGNED_16(FFTSample, ff_sin_8192[4096]);
+DECLARE_ALIGNED_16(FFTSample, ff_sin_16384[8192]);
+DECLARE_ALIGNED_16(FFTSample, ff_sin_32768[16384]);
+DECLARE_ALIGNED_16(FFTSample, ff_sin_65536[32768]);
+FFTSample *ff_sin_tabs[] = {
+    ff_sin_16, ff_sin_32, ff_sin_64, ff_sin_128, ff_sin_256, ff_sin_512, ff_sin_1024,
+    ff_sin_2048, ff_sin_4096, ff_sin_8192, ff_sin_16384, ff_sin_32768, ff_sin_65536,
+};
+
+av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
+{
+    int n = 1 << nbits;
+    int i;
+    const double theta = (trans == RDFT || trans == IRIDFT ? -1 : 1)*2*M_PI/n;
+
+    s->nbits           = nbits;
+    s->inverse         = trans == IRDFT || trans == IRIDFT;
+    s->sign_convention = trans == RIDFT || trans == IRIDFT ? 1 : -1;
+
+    if (nbits < 4 || nbits > 16)
+        return -1;
+
+    if (ff_fft_init(&s->fft, nbits-1, trans == IRDFT || trans == RIDFT) < 0)
+        return -1;
+
+    s->tcos = ff_cos_tabs[nbits-4];
+    s->tsin = ff_sin_tabs[nbits-4]+(trans == RDFT || trans == IRIDFT)*(n>>2);
+    for (i = 0; i < (n>>2); i++) {
+        s->tcos[i] = cos(i*theta);
+        s->tsin[i] = sin(i*theta);
+    }
+    return 0;
+}
+
+/** Map one real FFT into two parallel real even and odd FFTs. Then interleave
+ * the two real FFTs into one complex FFT. Unmangle the results.
+ * ref: http://www.engineeringproductivitytools.com/stuff/T0001/PT10.HTM
+ */
+void ff_rdft_calc_c(RDFTContext* s, FFTSample* data)
+{
+    int i, i1, i2;
+    FFTComplex ev, od;
+    const int n = 1 << s->nbits;
+    const float k1 = 0.5;
+    const float k2 = 0.5 - s->inverse;
+    const FFTSample *tcos = s->tcos;
+    const FFTSample *tsin = s->tsin;
+
+    if (!s->inverse) {
+        ff_fft_permute(&s->fft, (FFTComplex*)data);
+        ff_fft_calc(&s->fft, (FFTComplex*)data);
+    }
+    /* i=0 is a special case because of packing, the DC term is real, so we
+       are going to throw the N/2 term (also real) in with it. */
+    ev.re = data[0];
+    data[0] = ev.re+data[1];
+    data[1] = ev.re-data[1];
+    for (i = 1; i < (n>>2); i++) {
+        i1 = 2*i;
+        i2 = n-i1;
+        /* Separate even and odd FFTs */
+        ev.re =  k1*(data[i1  ]+data[i2  ]);
+        od.im = -k2*(data[i1  ]-data[i2  ]);
+        ev.im =  k1*(data[i1+1]-data[i2+1]);
+        od.re =  k2*(data[i1+1]+data[i2+1]);
+        /* Apply twiddle factors to the odd FFT and add to the even FFT */
+        data[i1  ] =  ev.re + od.re*tcos[i] - od.im*tsin[i];
+        data[i1+1] =  ev.im + od.im*tcos[i] + od.re*tsin[i];
+        data[i2  ] =  ev.re - od.re*tcos[i] + od.im*tsin[i];
+        data[i2+1] = -ev.im + od.im*tcos[i] + od.re*tsin[i];
+    }
+    data[2*i+1]=s->sign_convention*data[2*i+1];
+    if (s->inverse) {
+        data[0] *= k1;
+        data[1] *= k1;
+        ff_fft_permute(&s->fft, (FFTComplex*)data);
+        ff_fft_calc(&s->fft, (FFTComplex*)data);
+    }
+}
+
+void ff_rdft_calc(RDFTContext *s, FFTSample *data)
+{
+    ff_rdft_calc_c(s, data);
+}
+
+av_cold void ff_rdft_end(RDFTContext *s)
+{
+    ff_fft_end(&s->fft);
+}
-- 
cgit v1.2.3