/*
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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 <math.h>
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#include <audio_utils/sample.h>
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#define SAMPLE_NEG_MAX 0xFFFF
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#define SAMPLE_POS_MAX 0x7FFF
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#define SIGN_MASK 0x8000
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#define SIGN_BITS 1
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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 12
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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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#if SIGN_BITS + EXPONENT_BITS + MANTISSA_BITS != 16
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#error SIGN_BITS, EXPONENT_BITS and MANTISSA_BITS must sum to 16
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#endif
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sample_minifloat_t sample_from_float(float v)
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{
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if (isnan(v)) {
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return 0;
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}
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sample_minifloat_t sign = 0;
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if (v < 0.0f) {
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sign = SIGN_MASK;
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v = -v;
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}
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// This check could conceivably be tighter: v < constexpr float_from_sample(1).
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// Probably only useful to be made more accurate if this is changed to
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// manipulate the raw IEEE single precision float bit fields.
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if (v <= 0.0f) {
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// originally returned sign, but now seems better not to return negative 0
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return 0;
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}
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if (v >= 2.0f) {
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return SAMPLE_POS_MAX | sign;
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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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return SAMPLE_POS_MAX | sign;
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}
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if (-exp >= MANTISSA_BITS) {
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// originally returned sign, but now seems better not to return negative 0
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return 0;
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}
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int mantissa = (int) (r * ONE_FLOAT);
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sample_minifloat_t ret = exp > 0 ? (exp << MANTISSA_BITS) | (mantissa & ~HIDDEN_BIT) :
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(mantissa >> (1 - exp)) & MANTISSA_MAX;
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// ret != 0
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return ret | sign;
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}
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float float_from_sample(sample_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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float f = ldexpf((exponent > 0 ? HIDDEN_BIT | mantissa : mantissa << 1) / ONE_FLOAT,
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exponent - EXCESS);
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return a & SIGN_MASK ? -f : f;
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}
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