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 
gain_from_float(float v)35 gain_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 
float_from_gain(gain_minifloat_t a)56 float 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