1/*
2 * Copyright (C) 2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#include <math.h>
18#include <audio_utils/minifloat.h>
19
20#define EXPONENT_BITS   3
21#define EXPONENT_MAX    ((1 << EXPONENT_BITS) - 1)
22#define EXCESS          ((1 << EXPONENT_BITS) - 2)
23
24#define MANTISSA_BITS   13
25#define MANTISSA_MAX    ((1 << MANTISSA_BITS) - 1)
26#define HIDDEN_BIT      (1 << MANTISSA_BITS)
27#define ONE_FLOAT       ((float) (1 << (MANTISSA_BITS + 1)))
28
29#define MINIFLOAT_MAX   ((EXPONENT_MAX << MANTISSA_BITS) | MANTISSA_MAX)
30
31#if EXPONENT_BITS + MANTISSA_BITS != 16
32#error EXPONENT_BITS and MANTISSA_BITS must sum to 16
33#endif
34
35gain_minifloat_t gain_from_float(float v)
36{
37    if (isnan(v) || v <= 0.0f) {
38        return 0;
39    }
40    if (v >= 2.0f) {
41        return MINIFLOAT_MAX;
42    }
43    int exp;
44    float r = frexpf(v, &exp);
45    if ((exp += EXCESS) > EXPONENT_MAX) {
46        return MINIFLOAT_MAX;
47    }
48    if (-exp >= MANTISSA_BITS) {
49        return 0;
50    }
51    int mantissa = (int) (r * ONE_FLOAT);
52    return exp > 0 ? (exp << MANTISSA_BITS) | (mantissa & ~HIDDEN_BIT) :
53            (mantissa >> (1 - exp)) & MANTISSA_MAX;
54}
55
56float float_from_gain(gain_minifloat_t a)
57{
58    int mantissa = a & MANTISSA_MAX;
59    int exponent = (a >> MANTISSA_BITS) & EXPONENT_MAX;
60    return ldexpf((exponent > 0 ? HIDDEN_BIT | mantissa : mantissa << 1) / ONE_FLOAT,
61            exponent - EXCESS);
62}
63