Joonas Rikkonen
94 lines
3.3 KiB
C#
94 lines
3.3 KiB
C#
/* Copyright (c) 2006-2011 Skype Limited. All Rights Reserved
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Ported to C# by Logan Stromberg
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions
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are met:
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- Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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- Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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- Neither the name of Internet Society, IETF or IETF Trust, nor the
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names of specific contributors, may be used to endorse or promote
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products derived from this software without specific prior written
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permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
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OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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namespace Concentus.Silk
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{
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using Concentus.Common;
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using Concentus.Common.CPlusPlus;
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using Concentus.Silk.Enums;
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using Concentus.Silk.Structs;
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using System.Diagnostics;
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/// <summary>
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/// Approximate sigmoid function
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/// </summary>
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internal static class Sigmoid
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{
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private static readonly int[] sigm_LUT_slope_Q10 = {
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237, 153, 73, 30, 12, 7
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};
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private static readonly int[] sigm_LUT_pos_Q15 = {
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16384, 23955, 28861, 31213, 32178, 32548
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};
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private static readonly int[] sigm_LUT_neg_Q15 = {
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16384, 8812, 3906, 1554, 589, 219
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};
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internal static int silk_sigm_Q15(int in_Q5)
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{
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int ind;
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if (in_Q5 < 0)
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{
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/* Negative input */
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in_Q5 = -in_Q5;
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if (in_Q5 >= 6 * 32)
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{
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return 0; /* Clip */
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}
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else
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{
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/* Linear interpolation of look up table */
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ind = Inlines.silk_RSHIFT(in_Q5, 5);
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return (sigm_LUT_neg_Q15[ind] - Inlines.silk_SMULBB(sigm_LUT_slope_Q10[ind], in_Q5 & 0x1F));
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}
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}
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else
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{
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/* Positive input */
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if (in_Q5 >= 6 * 32)
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{
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return 32767; /* clip */
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}
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else
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{
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/* Linear interpolation of look up table */
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ind = Inlines.silk_RSHIFT(in_Q5, 5);
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return (sigm_LUT_pos_Q15[ind] + Inlines.silk_SMULBB(sigm_LUT_slope_Q10[ind], in_Q5 & 0x1F));
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}
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}
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}
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}
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}
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