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35 lines
1.1 KiB
35 lines
1.1 KiB
/*
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* Copyright 2013 Google Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <math.h>
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#include "synth.h"
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#include "log2.h"
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int32_t log2tab[LOG2_N_SAMPLES << 1];
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void Log2::init() {
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const double mul = 1 / log(2);
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for (int i = 0; i < LOG2_N_SAMPLES; i++) {
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double y = mul * log(i + (LOG2_N_SAMPLES)) + (7 - LOG2_LG_N_SAMPLES);
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log2tab[(i << 1) + 1] = (int32_t)floor(y * (1 << 24) + 0.5);
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}
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for (int i = 0; i < LOG2_N_SAMPLES - 1; i++) {
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log2tab[i << 1] = log2tab[(i << 1) + 3] - log2tab[(i << 1) + 1];
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}
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log2tab[(LOG2_N_SAMPLES << 1) - 2] = (8 << 24) - log2tab[(LOG2_N_SAMPLES << 1) - 1];
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}
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