From bb6f5690728486b71e280a295aef4c49d25ee758 Mon Sep 17 00:00:00 2001
From: Fabrice Bellard <fabrice@bellard.org>
Date: Mon, 28 Oct 2002 00:34:08 +0000
Subject: new generic FFT/MDCT code for audio codecs

Originally committed as revision 1088 to svn://svn.ffmpeg.org/ffmpeg/trunk
---
 libavcodec/mdct.c | 170 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 170 insertions(+)
 create mode 100644 libavcodec/mdct.c

(limited to 'libavcodec/mdct.c')

diff --git a/libavcodec/mdct.c b/libavcodec/mdct.c
new file mode 100644
index 0000000000..baab5d3152
--- /dev/null
+++ b/libavcodec/mdct.c
@@ -0,0 +1,170 @@
+/*
+ * MDCT/IMDCT transforms
+ * Copyright (c) 2002 Fabrice Bellard.
+ *
+ * This library 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 of the License, or (at your option) any later version.
+ *
+ * This library 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 this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+#include "dsputil.h"
+
+/*
+ * init MDCT or IMDCT computation
+ */
+int mdct_init(MDCTContext *s, int nbits, int inverse)
+{
+    int n, n4, i;
+    float alpha;
+
+    memset(s, 0, sizeof(*s));
+    n = 1 << nbits;
+    s->nbits = nbits;
+    s->n = n;
+    n4 = n >> 2;
+    s->tcos = malloc(n4 * sizeof(FFTSample));
+    if (!s->tcos)
+        goto fail;
+    s->tsin = malloc(n4 * sizeof(FFTSample));
+    if (!s->tsin)
+        goto fail;
+
+    for(i=0;i<n4;i++) {
+        alpha = 2 * M_PI * (i + 1.0 / 8.0) / n;
+        s->tcos[i] = -cos(alpha);
+        s->tsin[i] = -sin(alpha);
+    }
+    if (fft_init(&s->fft, s->nbits - 2, inverse) < 0)
+        goto fail;
+    return 0;
+ fail:
+    av_freep(&s->tcos);
+    av_freep(&s->tsin);
+    return -1;
+}
+
+/* complex multiplication: p = a * b */
+#define CMUL(pre, pim, are, aim, bre, bim) \
+{\
+    float _are = (are);\
+    float _aim = (aim);\
+    float _bre = (bre);\
+    float _bim = (bim);\
+    (pre) = _are * _bre - _aim * _bim;\
+    (pim) = _are * _bim + _aim * _bre;\
+}
+
+/**
+ * Compute inverse MDCT of size N = 2^nbits
+ * @param output N samples
+ * @param input N/2 samples
+ * @param tmp N/2 samples
+ */
+void imdct_calc(MDCTContext *s, FFTSample *output, 
+                const FFTSample *input, FFTSample *tmp)
+{
+    int k, n8, n4, n2, n, j;
+    const uint16_t *revtab = s->fft.revtab;
+    const FFTSample *tcos = s->tcos;
+    const FFTSample *tsin = s->tsin;
+    const FFTSample *in1, *in2;
+    FFTComplex *z = (FFTComplex *)tmp;
+
+    n = 1 << s->nbits;
+    n2 = n >> 1;
+    n4 = n >> 2;
+    n8 = n >> 3;
+
+    /* pre rotation */
+    in1 = input;
+    in2 = input + n2 - 1;
+    for(k = 0; k < n4; k++) {
+        j=revtab[k];
+        CMUL(z[j].re, z[j].im, *in2, *in1, tcos[k], tsin[k]);
+        in1 += 2;
+        in2 -= 2;
+    }
+    fft_calc(&s->fft, z);
+
+    /* post rotation + reordering */
+    /* XXX: optimize */
+    for(k = 0; k < n4; k++) {
+        CMUL(z[k].re, z[k].im, z[k].re, z[k].im, tcos[k], tsin[k]);
+    }
+    for(k = 0; k < n8; k++) {
+        output[2*k] = -z[n8 + k].im;
+        output[n2-1-2*k] = z[n8 + k].im;
+
+        output[2*k+1] = z[n8-1-k].re;
+        output[n2-1-2*k-1] = -z[n8-1-k].re;
+
+        output[n2 + 2*k]=-z[k+n8].re;
+        output[n-1- 2*k]=-z[k+n8].re;
+
+        output[n2 + 2*k+1]=z[n8-k-1].im;
+        output[n-2 - 2 * k] = z[n8-k-1].im;
+    }
+}
+
+/**
+ * Compute MDCT of size N = 2^nbits
+ * @param input N samples
+ * @param out N/2 samples
+ * @param tmp temporary storage of N/2 samples
+ */
+void mdct_calc(MDCTContext *s, FFTSample *out, 
+               const FFTSample *input, FFTSample *tmp)
+{
+    int i, j, n, n8, n4, n2, n3;
+    FFTSample re, im, re1, im1;
+    const uint16_t *revtab = s->fft.revtab;
+    const FFTSample *tcos = s->tcos;
+    const FFTSample *tsin = s->tsin;
+    FFTComplex *x = (FFTComplex *)tmp;
+
+    n = 1 << s->nbits;
+    n2 = n >> 1;
+    n4 = n >> 2;
+    n8 = n >> 3;
+    n3 = 3 * n4;
+
+    /* pre rotation */
+    for(i=0;i<n8;i++) {
+        re = -input[2*i+3*n4] - input[n3-1-2*i];
+        im = -input[n4+2*i] + input[n4-1-2*i];
+        j = revtab[i];
+        CMUL(x[j].re, x[j].im, re, im, -tcos[i], tsin[i]);
+
+        re = input[2*i] - input[n2-1-2*i];
+        im = -(input[n2+2*i] + input[n-1-2*i]);
+        j = revtab[n8 + i];
+        CMUL(x[j].re, x[j].im, re, im, -tcos[n8 + i], tsin[n8 + i]);
+    }
+
+    fft_calc(&s->fft, x);
+  
+    /* post rotation */
+    for(i=0;i<n4;i++) {
+        re = x[i].re;
+        im = x[i].im;
+        CMUL(re1, im1, re, im, -tsin[i], -tcos[i]);
+        out[2*i] = im1;
+        out[n2-1-2*i] = re1;
+    }
+}
+
+void mdct_end(MDCTContext *s)
+{
+    av_freep(&s->tcos);
+    av_freep(&s->tsin);
+    fft_end(&s->fft);
+}
-- 
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