cbrt_tablegen.h

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/*
 * Header file for hardcoded AAC cube-root table
 *
 * Copyright (c) 2010 Reimar Döffinger <Reimar.Doeffinger@gmx.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
 */
 
#ifndef AVCODEC_CBRT_TABLEGEN_H
#define AVCODEC_CBRT_TABLEGEN_H
 
#include <assert.h>
#include <stdint.h>
#include <math.h>
#include "libavutil/attributes.h"
#include "libavutil/intfloat.h"
#include "libavcodec/aac_defines.h"
#include "cbrt_data.h"
 
#if USE_FIXED
#define CBRT(x) lrint((x) * 8192)
#else
#define CBRT(x) av_float2int((float)(x))
#endif
 
union CBRT AAC_RENAME(ff_cbrt_tab_internal);
 
av_cold void AAC_RENAME(ff_cbrt_tableinit)(void)
{
    static_assert(2 * sizeof(AAC_RENAME(ff_cbrt_tab_internal).cbrt_tab[0])
                  >= sizeof(AAC_RENAME(ff_cbrt_tab_internal).tmp[0]),
                  "unexpected sizeofs");
    // We reuse ff_cbrt_tab_internal.tmp as a LUT (of doubles) for the roots
    // of the odd integers: tmp[idx] contains (2 * idx + 1)^{4/3}.
    ff_cbrt_dbl_tableinit(AAC_RENAME(ff_cbrt_tab_internal).tmp);
 
    double cbrt_2 = 2 * cbrt(2);
    for (int idx = TMP_LUT_SIZE - 1; idx >= 0; --idx) {
        double cbrt_val = AAC_RENAME(ff_cbrt_tab_internal).tmp[idx];
        // Due to i * sizeof(ff_cbrt_tab_internal.cbrt_tab[0]) >=
        // 2 * idx * sizeof(ff_cbrt_tab_internal.cbrt_tab[0])  >= idx * sizeof(double)
        // we don't clobber the double-LUT entries with index < idx
        // in the loop below. This is why we process idx in descending order.
        for (int i = 2 * idx + 1; i < LUT_SIZE; i *= 2) {
            AAC_RENAME(ff_cbrt_tab_internal).cbrt_tab[i] = CBRT(cbrt_val);
            cbrt_val *= cbrt_2;
        }
    }
    AAC_RENAME(ff_cbrt_tab_internal).cbrt_tab[0] = CBRT(0);
}
 
#endif /* AVCODEC_CBRT_TABLEGEN_H */