mirror of https://github.com/axmolengine/axmol.git
71 lines
2.0 KiB
C++
71 lines
2.0 KiB
C++
/*
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* Copyright (C) 2014 The Android Open Source Project
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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 <cmath>
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#include "audio/android/audio_utils/include/audio_utils/minifloat.h"
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#define EXPONENT_BITS 3
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#define EXPONENT_MAX ((1 << EXPONENT_BITS) - 1)
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#define EXCESS ((1 << EXPONENT_BITS) - 2)
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#define MANTISSA_BITS 13
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#define MANTISSA_MAX ((1 << MANTISSA_BITS) - 1)
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#define HIDDEN_BIT (1 << MANTISSA_BITS)
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#define ONE_FLOAT ((float) (1 << (MANTISSA_BITS + 1)))
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#define MINIFLOAT_MAX ((EXPONENT_MAX << MANTISSA_BITS) | MANTISSA_MAX)
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#if EXPONENT_BITS + MANTISSA_BITS != 16
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#error EXPONENT_BITS and MANTISSA_BITS must sum to 16
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#endif
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extern "C" {
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gain_minifloat_t gain_from_float(float v)
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{
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if (std::isnan(v) || v <= 0.0f)
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{
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return 0;
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}
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if (v >= 2.0f)
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{
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return MINIFLOAT_MAX;
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}
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int exp;
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float r = frexpf(v, &exp);
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if ((exp += EXCESS) > EXPONENT_MAX)
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{
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return MINIFLOAT_MAX;
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}
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if (-exp >= MANTISSA_BITS)
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{
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return 0;
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}
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int mantissa = (int) (r * ONE_FLOAT);
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return exp > 0 ? (exp << MANTISSA_BITS) | (mantissa & ~HIDDEN_BIT) :
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(mantissa >> (1 - exp)) & MANTISSA_MAX;
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}
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float float_from_gain(gain_minifloat_t a)
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{
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int mantissa = a & MANTISSA_MAX;
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int exponent = (a >> MANTISSA_BITS) & EXPONENT_MAX;
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return ldexpf((exponent > 0 ? HIDDEN_BIT | mantissa : mantissa << 1) / ONE_FLOAT,
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exponent - EXCESS);
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}
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} // extern "C" {
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