Move fixed-point parts of the AC-3 encoder to separate files.

Originally committed as revision 26206 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/Makefile

@@ -54,7 +54,7 @@ OBJS-$(CONFIG_AAC_ENCODER)             += aacenc.o aaccoder.o    \
                                           mpeg4audio.o
 OBJS-$(CONFIG_AASC_DECODER)            += aasc.o msrledec.o
 OBJS-$(CONFIG_AC3_DECODER)             += ac3dec.o ac3dec_data.o ac3.o
-OBJS-$(CONFIG_AC3_ENCODER)             += ac3enc.o ac3tab.o ac3.o
+OBJS-$(CONFIG_AC3_ENCODER)             += ac3enc_fixed.o ac3tab.o ac3.o
 OBJS-$(CONFIG_ALAC_DECODER)            += alac.o
 OBJS-$(CONFIG_ALAC_ENCODER)            += alacenc.o
 OBJS-$(CONFIG_ALS_DECODER)             += alsdec.o bgmc.o mpeg4audio.o

libavcodec/ac3enc.c

@@ -43,34 +43,10 @@
 /** Scale a float value by 2^bits and convert to an integer. */
 #define SCALE_FLOAT(a, bits) lrintf((a) * (float)(1 << (bits)))
 
-typedef int16_t SampleType;
-typedef int32_t CoefType;
 
-#define SCALE_COEF(a) (a)
-
-/** Scale a float value by 2^15, convert to an integer, and clip to range -32767..32767. */
-#define FIX15(a) av_clip(SCALE_FLOAT(a, 15), -32767, 32767)
+#include "ac3enc_fixed.h"
 
 
-/**
- * Compex number.
- * Used in fixed-point MDCT calculation.
- */
-typedef struct IComplex {
-    int16_t re,im;
-} IComplex;
-
-typedef struct AC3MDCTContext {
-    const int16_t *window;                  ///< MDCT window function
-    int nbits;                              ///< log2(transform size)
-    int16_t *costab;                        ///< FFT cos table
-    int16_t *sintab;                        ///< FFT sin table
-    int16_t *xcos1;                         ///< MDCT cos table
-    int16_t *xsin1;                         ///< MDCT sin table
-    int16_t *rot_tmp;                       ///< temp buffer for pre-rotated samples
-    IComplex *cplx_tmp;                     ///< temp buffer for complex pre-rotated samples
-} AC3MDCTContext;
-
 /**
  * Data for a single audio block.
  */
@@ -154,6 +130,21 @@ typedef struct AC3EncodeContext {
 } AC3EncodeContext;
 
 
+/* prototypes for functions in ac3enc_fixed.c */
+
+static av_cold void mdct_end(AC3MDCTContext *mdct);
+
+static av_cold int mdct_init(AVCodecContext *avctx, AC3MDCTContext *mdct,
+                             int nbits);
+
+static void mdct512(AC3MDCTContext *mdct, CoefType *out, SampleType *in);
+
+static void apply_window(SampleType *output, const SampleType *input,
+                         const SampleType *window, int n);
+
+static int normalize_samples(AC3EncodeContext *s);
+
+
 /**
  * LUT for number of exponent groups.
  * exponent_group_tab[exponent strategy-1][number of coefficients]
@@ -233,291 +224,6 @@ static void deinterleave_input_samples(AC3EncodeContext *s,
 }
 
 
-/**
- * Finalize MDCT and free allocated memory.
- */
-static av_cold void mdct_end(AC3MDCTContext *mdct)
-{
-    mdct->nbits = 0;
-    av_freep(&mdct->costab);
-    av_freep(&mdct->sintab);
-    av_freep(&mdct->xcos1);
-    av_freep(&mdct->xsin1);
-    av_freep(&mdct->rot_tmp);
-    av_freep(&mdct->cplx_tmp);
-}
-
-
-/**
- * Initialize FFT tables.
- * @param ln log2(FFT size)
- */
-static av_cold int fft_init(AVCodecContext *avctx, AC3MDCTContext *mdct, int ln)
-{
-    int i, n, n2;
-    float alpha;
-
-    n  = 1 << ln;
-    n2 = n >> 1;
-
-    FF_ALLOC_OR_GOTO(avctx, mdct->costab, n2 * sizeof(*mdct->costab), fft_alloc_fail);
-    FF_ALLOC_OR_GOTO(avctx, mdct->sintab, n2 * sizeof(*mdct->sintab), fft_alloc_fail);
-
-    for (i = 0; i < n2; i++) {
-        alpha     = 2.0 * M_PI * i / n;
-        mdct->costab[i] = FIX15(cos(alpha));
-        mdct->sintab[i] = FIX15(sin(alpha));
-    }
-
-    return 0;
-fft_alloc_fail:
-    mdct_end(mdct);
-    return AVERROR(ENOMEM);
-}
-
-
-/**
- * Initialize MDCT tables.
- * @param nbits log2(MDCT size)
- */
-static av_cold int mdct_init(AVCodecContext *avctx, AC3MDCTContext *mdct,
-                             int nbits)
-{
-    int i, n, n4, ret;
-
-    n  = 1 << nbits;
-    n4 = n >> 2;
-
-    mdct->nbits = nbits;
-
-    ret = fft_init(avctx, mdct, nbits - 2);
-    if (ret)
-        return ret;
-
-    mdct->window = ff_ac3_window;
-
-    FF_ALLOC_OR_GOTO(avctx, mdct->xcos1,    n4 * sizeof(*mdct->xcos1),    mdct_alloc_fail);
-    FF_ALLOC_OR_GOTO(avctx, mdct->xsin1,    n4 * sizeof(*mdct->xsin1),    mdct_alloc_fail);
-    FF_ALLOC_OR_GOTO(avctx, mdct->rot_tmp,  n  * sizeof(*mdct->rot_tmp),  mdct_alloc_fail);
-    FF_ALLOC_OR_GOTO(avctx, mdct->cplx_tmp, n4 * sizeof(*mdct->cplx_tmp), mdct_alloc_fail);
-
-    for (i = 0; i < n4; i++) {
-        float alpha = 2.0 * M_PI * (i + 1.0 / 8.0) / n;
-        mdct->xcos1[i] = FIX15(-cos(alpha));
-        mdct->xsin1[i] = FIX15(-sin(alpha));
-    }
-
-    return 0;
-mdct_alloc_fail:
-    mdct_end(mdct);
-    return AVERROR(ENOMEM);
-}
-
-
-/** Butterfly op */
-#define BF(pre, pim, qre, qim, pre1, pim1, qre1, qim1)  \
-{                                                       \
-  int ax, ay, bx, by;                                   \
-  bx  = pre1;                                           \
-  by  = pim1;                                           \
-  ax  = qre1;                                           \
-  ay  = qim1;                                           \
-  pre = (bx + ax) >> 1;                                 \
-  pim = (by + ay) >> 1;                                 \
-  qre = (bx - ax) >> 1;                                 \
-  qim = (by - ay) >> 1;                                 \
-}
-
-
-/** Complex multiply */
-#define CMUL(pre, pim, are, aim, bre, bim)              \
-{                                                       \
-   pre = (MUL16(are, bre) - MUL16(aim, bim)) >> 15;     \
-   pim = (MUL16(are, bim) + MUL16(bre, aim)) >> 15;     \
-}
-
-
-/**
- * Calculate a 2^n point complex FFT on 2^ln points.
- * @param z  complex input/output samples
- * @param ln log2(FFT size)
- */
-static void fft(AC3MDCTContext *mdct, IComplex *z, int ln)
-{
-    int j, l, np, np2;
-    int nblocks, nloops;
-    register IComplex *p,*q;
-    int tmp_re, tmp_im;
-
-    np = 1 << ln;
-
-    /* reverse */
-    for (j = 0; j < np; j++) {
-        int k = av_reverse[j] >> (8 - ln);
-        if (k < j)
-            FFSWAP(IComplex, z[k], z[j]);
-    }
-
-    /* pass 0 */
-
-    p = &z[0];
-    j = np >> 1;
-    do {
-        BF(p[0].re, p[0].im, p[1].re, p[1].im,
-           p[0].re, p[0].im, p[1].re, p[1].im);
-        p += 2;
-    } while (--j);
-
-    /* pass 1 */
-
-    p = &z[0];
-    j = np >> 2;
-    do {
-        BF(p[0].re, p[0].im, p[2].re,  p[2].im,
-           p[0].re, p[0].im, p[2].re,  p[2].im);
-        BF(p[1].re, p[1].im, p[3].re,  p[3].im,
-           p[1].re, p[1].im, p[3].im, -p[3].re);
-        p+=4;
-    } while (--j);
-
-    /* pass 2 .. ln-1 */
-
-    nblocks = np >> 3;
-    nloops  =  1 << 2;
-    np2     = np >> 1;
-    do {
-        p = z;
-        q = z + nloops;
-        for (j = 0; j < nblocks; j++) {
-            BF(p->re, p->im, q->re, q->im,
-               p->re, p->im, q->re, q->im);
-            p++;
-            q++;
-            for(l = nblocks; l < np2; l += nblocks) {
-                CMUL(tmp_re, tmp_im, mdct->costab[l], -mdct->sintab[l], q->re, q->im);
-                BF(p->re, p->im, q->re,  q->im,
-                   p->re, p->im, tmp_re, tmp_im);
-                p++;
-                q++;
-            }
-            p += nloops;
-            q += nloops;
-        }
-        nblocks = nblocks >> 1;
-        nloops  = nloops  << 1;
-    } while (nblocks);
-}
-
-
-/**
- * Calculate a 512-point MDCT
- * @param out 256 output frequency coefficients
- * @param in  512 windowed input audio samples
- */
-static void mdct512(AC3MDCTContext *mdct, int32_t *out, int16_t *in)
-{
-    int i, re, im, n, n2, n4;
-    int16_t *rot = mdct->rot_tmp;
-    IComplex *x  = mdct->cplx_tmp;
-
-    n  = 1 << mdct->nbits;
-    n2 = n >> 1;
-    n4 = n >> 2;
-
-    /* shift to simplify computations */
-    for (i = 0; i <n4; i++)
-        rot[i] = -in[i + 3*n4];
-    memcpy(&rot[n4], &in[0], 3*n4*sizeof(*in));
-
-    /* pre rotation */
-    for (i = 0; i < n4; i++) {
-        re =  ((int)rot[   2*i] - (int)rot[ n-1-2*i]) >> 1;
-        im = -((int)rot[n2+2*i] - (int)rot[n2-1-2*i]) >> 1;
-        CMUL(x[i].re, x[i].im, re, im, -mdct->xcos1[i], mdct->xsin1[i]);
-    }
-
-    fft(mdct, x, mdct->nbits - 2);
-
-    /* post rotation */
-    for (i = 0; i < n4; i++) {
-        re = x[i].re;
-        im = x[i].im;
-        CMUL(out[n2-1-2*i], out[2*i], re, im, mdct->xsin1[i], mdct->xcos1[i]);
-    }
-}
-
-
-/**
- * Apply KBD window to input samples prior to MDCT.
- */
-static void apply_window(int16_t *output, const int16_t *input,
-                         const int16_t *window, int n)
-{
-    int i;
-    int n2 = n >> 1;
-
-    for (i = 0; i < n2; i++) {
-        output[i]     = MUL16(input[i],     window[i]) >> 15;
-        output[n-i-1] = MUL16(input[n-i-1], window[i]) >> 15;
-    }
-}
-
-
-/**
- * Calculate the log2() of the maximum absolute value in an array.
- * @param tab input array
- * @param n   number of values in the array
- * @return    log2(max(abs(tab[])))
- */
-static int log2_tab(int16_t *tab, int n)
-{
-    int i, v;
-
-    v = 0;
-    for (i = 0; i < n; i++)
-        v |= abs(tab[i]);
-
-    return av_log2(v);
-}
-
-
-/**
- * Left-shift each value in an array by a specified amount.
- * @param tab    input array
- * @param n      number of values in the array
- * @param lshift left shift amount. a negative value means right shift.
- */
-static void lshift_tab(int16_t *tab, int n, int lshift)
-{
-    int i;
-
-    if (lshift > 0) {
-        for (i = 0; i < n; i++)
-            tab[i] <<= lshift;
-    } else if (lshift < 0) {
-        lshift = -lshift;
-        for (i = 0; i < n; i++)
-            tab[i] >>= lshift;
-    }
-}
-
-
-/**
- * Normalize the input samples to use the maximum available precision.
- * This assumes signed 16-bit input samples. Exponents are reduced by 9 to
- * match the 24-bit internal precision for MDCT coefficients.
- *
- * @return exponent shift
- */
-static int normalize_samples(AC3EncodeContext *s)
-{
-    int v = 14 - log2_tab(s->windowed_samples, AC3_WINDOW_SIZE);
-    v = FFMAX(0, v);
-    lshift_tab(s->windowed_samples, AC3_WINDOW_SIZE, v);
-    return v - 9;
-}
-
-
 /**
  * Apply the MDCT to input samples to generate frequency coefficients.
  * This applies the KBD window and normalizes the input to reduce precision
@@ -1982,113 +1688,3 @@ init_fail:
     ac3_encode_close(avctx);
     return ret;
 }
-
-
-#ifdef TEST
-/*************************************************************************/
-/* TEST */
-
-#include "libavutil/lfg.h"
-
-#define MDCT_NBITS 9
-#define MDCT_SAMPLES (1 << MDCT_NBITS)
-#define FN (MDCT_SAMPLES/4)
-
-
-static void fft_test(AC3MDCTContext *mdct, AVLFG *lfg)
-{
-    IComplex in[FN], in1[FN];
-    int k, n, i;
-    float sum_re, sum_im, a;
-
-    for (i = 0; i < FN; i++) {
-        in[i].re = av_lfg_get(lfg) % 65535 - 32767;
-        in[i].im = av_lfg_get(lfg) % 65535 - 32767;
-        in1[i]   = in[i];
-    }
-    fft(mdct, in, 7);
-
-    /* do it by hand */
-    for (k = 0; k < FN; k++) {
-        sum_re = 0;
-        sum_im = 0;
-        for (n = 0; n < FN; n++) {
-            a = -2 * M_PI * (n * k) / FN;
-            sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);
-            sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);
-        }
-        av_log(NULL, AV_LOG_DEBUG, "%3d: %6d,%6d %6.0f,%6.0f\n",
-               k, in[k].re, in[k].im, sum_re / FN, sum_im / FN);
-    }
-}
-
-
-static void mdct_test(AC3MDCTContext *mdct, AVLFG *lfg)
-{
-    int16_t input[MDCT_SAMPLES];
-    int32_t output[AC3_MAX_COEFS];
-    float input1[MDCT_SAMPLES];
-    float output1[AC3_MAX_COEFS];
-    float s, a, err, e, emax;
-    int i, k, n;
-
-    for (i = 0; i < MDCT_SAMPLES; i++) {
-        input[i]  = (av_lfg_get(lfg) % 65535 - 32767) * 9 / 10;
-        input1[i] = input[i];
-    }
-
-    mdct512(mdct, output, input);
-
-    /* do it by hand */
-    for (k = 0; k < AC3_MAX_COEFS; k++) {
-        s = 0;
-        for (n = 0; n < MDCT_SAMPLES; n++) {
-            a = (2*M_PI*(2*n+1+MDCT_SAMPLES/2)*(2*k+1) / (4 * MDCT_SAMPLES));
-            s += input1[n] * cos(a);
-        }
-        output1[k] = -2 * s / MDCT_SAMPLES;
-    }
-
-    err  = 0;
-    emax = 0;
-    for (i = 0; i < AC3_MAX_COEFS; i++) {
-        av_log(NULL, AV_LOG_DEBUG, "%3d: %7d %7.0f\n", i, output[i], output1[i]);
-        e = output[i] - output1[i];
-        if (e > emax)
-            emax = e;
-        err += e * e;
-    }
-    av_log(NULL, AV_LOG_DEBUG, "err2=%f emax=%f\n", err / AC3_MAX_COEFS, emax);
-}
-
-
-int main(void)
-{
-    AVLFG lfg;
-    AC3MDCTContext mdct;
-
-    mdct.avctx = NULL;
-    av_log_set_level(AV_LOG_DEBUG);
-    mdct_init(&mdct, 9);
-
-    fft_test(&mdct, &lfg);
-    mdct_test(&mdct, &lfg);
-
-    return 0;
-}
-#endif /* TEST */
-
-
-AVCodec ac3_encoder = {
-    "ac3",
-    AVMEDIA_TYPE_AUDIO,
-    CODEC_ID_AC3,
-    sizeof(AC3EncodeContext),
-    ac3_encode_init,
-    ac3_encode_frame,
-    ac3_encode_close,
-    NULL,
-    .sample_fmts = (const enum AVSampleFormat[]){AV_SAMPLE_FMT_S16,AV_SAMPLE_FMT_NONE},
-    .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
-    .channel_layouts = ac3_channel_layouts,
-};

libavcodec/ac3enc_fixed.c

@@ -0,0 +1,428 @@
+/*
+ * The simplest AC-3 encoder
+ * Copyright (c) 2000 Fabrice Bellard
+ * Copyright (c) 2006-2010 Justin Ruggles <justin.ruggles@gmail.com>
+ * Copyright (c) 2006-2010 Prakash Punnoor <prakash@punnoor.de>
+ *
+ * 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
+ * fixed-point AC-3 encoder.
+ */
+
+#include "ac3enc.c"
+
+
+/** Scale a float value by 2^15, convert to an integer, and clip to range -32767..32767. */
+#define FIX15(a) av_clip(SCALE_FLOAT(a, 15), -32767, 32767)
+
+
+/**
+ * Finalize MDCT and free allocated memory.
+ */
+static av_cold void mdct_end(AC3MDCTContext *mdct)
+{
+    mdct->nbits = 0;
+    av_freep(&mdct->costab);
+    av_freep(&mdct->sintab);
+    av_freep(&mdct->xcos1);
+    av_freep(&mdct->xsin1);
+    av_freep(&mdct->rot_tmp);
+    av_freep(&mdct->cplx_tmp);
+}
+
+
+/**
+ * Initialize FFT tables.
+ * @param ln log2(FFT size)
+ */
+static av_cold int fft_init(AVCodecContext *avctx, AC3MDCTContext *mdct, int ln)
+{
+    int i, n, n2;
+    float alpha;
+
+    n  = 1 << ln;
+    n2 = n >> 1;
+
+    FF_ALLOC_OR_GOTO(avctx, mdct->costab, n2 * sizeof(*mdct->costab), fft_alloc_fail);
+    FF_ALLOC_OR_GOTO(avctx, mdct->sintab, n2 * sizeof(*mdct->sintab), fft_alloc_fail);
+
+    for (i = 0; i < n2; i++) {
+        alpha     = 2.0 * M_PI * i / n;
+        mdct->costab[i] = FIX15(cos(alpha));
+        mdct->sintab[i] = FIX15(sin(alpha));
+    }
+
+    return 0;
+fft_alloc_fail:
+    mdct_end(mdct);
+    return AVERROR(ENOMEM);
+}
+
+
+/**
+ * Initialize MDCT tables.
+ * @param nbits log2(MDCT size)
+ */
+static av_cold int mdct_init(AVCodecContext *avctx, AC3MDCTContext *mdct,
+                             int nbits)
+{
+    int i, n, n4, ret;
+
+    n  = 1 << nbits;
+    n4 = n >> 2;
+
+    mdct->nbits = nbits;
+
+    ret = fft_init(avctx, mdct, nbits - 2);
+    if (ret)
+        return ret;
+
+    mdct->window = ff_ac3_window;
+
+    FF_ALLOC_OR_GOTO(avctx, mdct->xcos1,    n4 * sizeof(*mdct->xcos1),    mdct_alloc_fail);
+    FF_ALLOC_OR_GOTO(avctx, mdct->xsin1,    n4 * sizeof(*mdct->xsin1),    mdct_alloc_fail);
+    FF_ALLOC_OR_GOTO(avctx, mdct->rot_tmp,  n  * sizeof(*mdct->rot_tmp),  mdct_alloc_fail);
+    FF_ALLOC_OR_GOTO(avctx, mdct->cplx_tmp, n4 * sizeof(*mdct->cplx_tmp), mdct_alloc_fail);
+
+    for (i = 0; i < n4; i++) {
+        float alpha = 2.0 * M_PI * (i + 1.0 / 8.0) / n;
+        mdct->xcos1[i] = FIX15(-cos(alpha));
+        mdct->xsin1[i] = FIX15(-sin(alpha));
+    }
+
+    return 0;
+mdct_alloc_fail:
+    mdct_end(mdct);
+    return AVERROR(ENOMEM);
+}
+
+
+/** Butterfly op */
+#define BF(pre, pim, qre, qim, pre1, pim1, qre1, qim1)  \
+{                                                       \
+  int ax, ay, bx, by;                                   \
+  bx  = pre1;                                           \
+  by  = pim1;                                           \
+  ax  = qre1;                                           \
+  ay  = qim1;                                           \
+  pre = (bx + ax) >> 1;                                 \
+  pim = (by + ay) >> 1;                                 \
+  qre = (bx - ax) >> 1;                                 \
+  qim = (by - ay) >> 1;                                 \
+}
+
+
+/** Complex multiply */
+#define CMUL(pre, pim, are, aim, bre, bim)              \
+{                                                       \
+   pre = (MUL16(are, bre) - MUL16(aim, bim)) >> 15;     \
+   pim = (MUL16(are, bim) + MUL16(bre, aim)) >> 15;     \
+}
+
+
+/**
+ * Calculate a 2^n point complex FFT on 2^ln points.
+ * @param z  complex input/output samples
+ * @param ln log2(FFT size)
+ */
+static void fft(AC3MDCTContext *mdct, IComplex *z, int ln)
+{
+    int j, l, np, np2;
+    int nblocks, nloops;
+    register IComplex *p,*q;
+    int tmp_re, tmp_im;
+
+    np = 1 << ln;
+
+    /* reverse */
+    for (j = 0; j < np; j++) {
+        int k = av_reverse[j] >> (8 - ln);
+        if (k < j)
+            FFSWAP(IComplex, z[k], z[j]);
+    }
+
+    /* pass 0 */
+
+    p = &z[0];
+    j = np >> 1;
+    do {
+        BF(p[0].re, p[0].im, p[1].re, p[1].im,
+           p[0].re, p[0].im, p[1].re, p[1].im);
+        p += 2;
+    } while (--j);
+
+    /* pass 1 */
+
+    p = &z[0];
+    j = np >> 2;
+    do {
+        BF(p[0].re, p[0].im, p[2].re,  p[2].im,
+           p[0].re, p[0].im, p[2].re,  p[2].im);
+        BF(p[1].re, p[1].im, p[3].re,  p[3].im,
+           p[1].re, p[1].im, p[3].im, -p[3].re);
+        p+=4;
+    } while (--j);
+
+    /* pass 2 .. ln-1 */
+
+    nblocks = np >> 3;
+    nloops  =  1 << 2;
+    np2     = np >> 1;
+    do {
+        p = z;
+        q = z + nloops;
+        for (j = 0; j < nblocks; j++) {
+            BF(p->re, p->im, q->re, q->im,
+               p->re, p->im, q->re, q->im);
+            p++;
+            q++;
+            for(l = nblocks; l < np2; l += nblocks) {
+                CMUL(tmp_re, tmp_im, mdct->costab[l], -mdct->sintab[l], q->re, q->im);
+                BF(p->re, p->im, q->re,  q->im,
+                   p->re, p->im, tmp_re, tmp_im);
+                p++;
+                q++;
+            }
+            p += nloops;
+            q += nloops;
+        }
+        nblocks = nblocks >> 1;
+        nloops  = nloops  << 1;
+    } while (nblocks);
+}
+
+
+/**
+ * Calculate a 512-point MDCT
+ * @param out 256 output frequency coefficients
+ * @param in  512 windowed input audio samples
+ */
+static void mdct512(AC3MDCTContext *mdct, int32_t *out, int16_t *in)
+{
+    int i, re, im, n, n2, n4;
+    int16_t *rot = mdct->rot_tmp;
+    IComplex *x  = mdct->cplx_tmp;
+
+    n  = 1 << mdct->nbits;
+    n2 = n >> 1;
+    n4 = n >> 2;
+
+    /* shift to simplify computations */
+    for (i = 0; i <n4; i++)
+        rot[i] = -in[i + 3*n4];
+    memcpy(&rot[n4], &in[0], 3*n4*sizeof(*in));
+
+    /* pre rotation */
+    for (i = 0; i < n4; i++) {
+        re =  ((int)rot[   2*i] - (int)rot[ n-1-2*i]) >> 1;
+        im = -((int)rot[n2+2*i] - (int)rot[n2-1-2*i]) >> 1;
+        CMUL(x[i].re, x[i].im, re, im, -mdct->xcos1[i], mdct->xsin1[i]);
+    }
+
+    fft(mdct, x, mdct->nbits - 2);
+
+    /* post rotation */
+    for (i = 0; i < n4; i++) {
+        re = x[i].re;
+        im = x[i].im;
+        CMUL(out[n2-1-2*i], out[2*i], re, im, mdct->xsin1[i], mdct->xcos1[i]);
+    }
+}
+
+
+/**
+ * Apply KBD window to input samples prior to MDCT.
+ */
+static void apply_window(int16_t *output, const int16_t *input,
+                         const int16_t *window, int n)
+{
+    int i;
+    int n2 = n >> 1;
+
+    for (i = 0; i < n2; i++) {
+        output[i]     = MUL16(input[i],     window[i]) >> 15;
+        output[n-i-1] = MUL16(input[n-i-1], window[i]) >> 15;
+    }
+}
+
+
+/**
+ * Calculate the log2() of the maximum absolute value in an array.
+ * @param tab input array
+ * @param n   number of values in the array
+ * @return    log2(max(abs(tab[])))
+ */
+static int log2_tab(int16_t *tab, int n)
+{
+    int i, v;
+
+    v = 0;
+    for (i = 0; i < n; i++)
+        v |= abs(tab[i]);
+
+    return av_log2(v);
+}
+
+
+/**
+ * Left-shift each value in an array by a specified amount.
+ * @param tab    input array
+ * @param n      number of values in the array
+ * @param lshift left shift amount. a negative value means right shift.
+ */
+static void lshift_tab(int16_t *tab, int n, int lshift)
+{
+    int i;
+
+    if (lshift > 0) {
+        for (i = 0; i < n; i++)
+            tab[i] <<= lshift;
+    } else if (lshift < 0) {
+        lshift = -lshift;
+        for (i = 0; i < n; i++)
+            tab[i] >>= lshift;
+    }
+}
+
+
+/**
+ * Normalize the input samples to use the maximum available precision.
+ * This assumes signed 16-bit input samples. Exponents are reduced by 9 to
+ * match the 24-bit internal precision for MDCT coefficients.
+ *
+ * @return exponent shift
+ */
+static int normalize_samples(AC3EncodeContext *s)
+{
+    int v = 14 - log2_tab(s->windowed_samples, AC3_WINDOW_SIZE);
+    v = FFMAX(0, v);
+    lshift_tab(s->windowed_samples, AC3_WINDOW_SIZE, v);
+    return v - 9;
+}
+
+
+#ifdef TEST
+/*************************************************************************/
+/* TEST */
+
+#include "libavutil/lfg.h"
+
+#define MDCT_NBITS 9
+#define MDCT_SAMPLES (1 << MDCT_NBITS)
+#define FN (MDCT_SAMPLES/4)
+
+
+static void fft_test(AC3MDCTContext *mdct, AVLFG *lfg)
+{
+    IComplex in[FN], in1[FN];
+    int k, n, i;
+    float sum_re, sum_im, a;
+
+    for (i = 0; i < FN; i++) {
+        in[i].re = av_lfg_get(lfg) % 65535 - 32767;
+        in[i].im = av_lfg_get(lfg) % 65535 - 32767;
+        in1[i]   = in[i];
+    }
+    fft(mdct, in, 7);
+
+    /* do it by hand */
+    for (k = 0; k < FN; k++) {
+        sum_re = 0;
+        sum_im = 0;
+        for (n = 0; n < FN; n++) {
+            a = -2 * M_PI * (n * k) / FN;
+            sum_re += in1[n].re * cos(a) - in1[n].im * sin(a);
+            sum_im += in1[n].re * sin(a) + in1[n].im * cos(a);
+        }
+        av_log(NULL, AV_LOG_DEBUG, "%3d: %6d,%6d %6.0f,%6.0f\n",
+               k, in[k].re, in[k].im, sum_re / FN, sum_im / FN);
+    }
+}
+
+
+static void mdct_test(AC3MDCTContext *mdct, AVLFG *lfg)
+{
+    int16_t input[MDCT_SAMPLES];
+    int32_t output[AC3_MAX_COEFS];
+    float input1[MDCT_SAMPLES];
+    float output1[AC3_MAX_COEFS];
+    float s, a, err, e, emax;
+    int i, k, n;
+
+    for (i = 0; i < MDCT_SAMPLES; i++) {
+        input[i]  = (av_lfg_get(lfg) % 65535 - 32767) * 9 / 10;
+        input1[i] = input[i];
+    }
+
+    mdct512(mdct, output, input);
+
+    /* do it by hand */
+    for (k = 0; k < AC3_MAX_COEFS; k++) {
+        s = 0;
+        for (n = 0; n < MDCT_SAMPLES; n++) {
+            a = (2*M_PI*(2*n+1+MDCT_SAMPLES/2)*(2*k+1) / (4 * MDCT_SAMPLES));
+            s += input1[n] * cos(a);
+        }
+        output1[k] = -2 * s / MDCT_SAMPLES;
+    }
+
+    err  = 0;
+    emax = 0;
+    for (i = 0; i < AC3_MAX_COEFS; i++) {
+        av_log(NULL, AV_LOG_DEBUG, "%3d: %7d %7.0f\n", i, output[i], output1[i]);
+        e = output[i] - output1[i];
+        if (e > emax)
+            emax = e;
+        err += e * e;
+    }
+    av_log(NULL, AV_LOG_DEBUG, "err2=%f emax=%f\n", err / AC3_MAX_COEFS, emax);
+}
+
+
+int main(void)
+{
+    AVLFG lfg;
+    AC3MDCTContext mdct;
+
+    mdct.avctx = NULL;
+    av_log_set_level(AV_LOG_DEBUG);
+    mdct_init(&mdct, 9);
+
+    fft_test(&mdct, &lfg);
+    mdct_test(&mdct, &lfg);
+
+    return 0;
+}
+#endif /* TEST */
+
+
+AVCodec ac3_encoder = {
+    "ac3",
+    AVMEDIA_TYPE_AUDIO,
+    CODEC_ID_AC3,
+    sizeof(AC3EncodeContext),
+    ac3_encode_init,
+    ac3_encode_frame,
+    ac3_encode_close,
+    NULL,
+    .sample_fmts = (const enum AVSampleFormat[]){AV_SAMPLE_FMT_S16,AV_SAMPLE_FMT_NONE},
+    .long_name = NULL_IF_CONFIG_SMALL("ATSC A/52A (AC-3)"),
+    .channel_layouts = ac3_channel_layouts,
+};

libavcodec/ac3enc_fixed.h

@@ -0,0 +1,60 @@
+/*
+ * The simplest AC-3 encoder
+ * Copyright (c) 2000 Fabrice Bellard
+ * Copyright (c) 2006-2010 Justin Ruggles <justin.ruggles@gmail.com>
+ * Copyright (c) 2006-2010 Prakash Punnoor <prakash@punnoor.de>
+ *
+ * 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
+ * fixed-point AC-3 encoder header.
+ */
+
+#ifndef AVCODEC_AC3ENC_FIXED_H
+#define AVCODEC_AC3ENC_FIXED_H
+
+#include <stdint.h>
+
+
+typedef int16_t SampleType;
+typedef int32_t CoefType;
+
+#define SCALE_COEF(a) (a)
+
+
+/**
+ * Compex number.
+ * Used in fixed-point MDCT calculation.
+ */
+typedef struct IComplex {
+    int16_t re,im;
+} IComplex;
+
+typedef struct AC3MDCTContext {
+    const int16_t *window;                  ///< MDCT window function
+    int nbits;                              ///< log2(transform size)
+    int16_t *costab;                        ///< FFT cos table
+    int16_t *sintab;                        ///< FFT sin table
+    int16_t *xcos1;                         ///< MDCT cos table
+    int16_t *xsin1;                         ///< MDCT sin table
+    int16_t *rot_tmp;                       ///< temp buffer for pre-rotated samples
+    IComplex *cplx_tmp;                     ///< temp buffer for complex pre-rotated samples
+} AC3MDCTContext;
+
+#endif /* AVCODEC_AC3ENC_FIXED_H */