2 * Copyright (C) 2014 The Android Open Source Project
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
8 * http://www.apache.org/licenses/LICENSE-2.0
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.
18 #include <audio_utils/sample.h>
20 #define SAMPLE_NEG_MAX 0xFFFF
21 #define SAMPLE_POS_MAX 0x7FFF
23 #define SIGN_MASK 0x8000
26 #define EXPONENT_BITS 3
27 #define EXPONENT_MAX ((1 << EXPONENT_BITS) - 1)
28 #define EXCESS ((1 << EXPONENT_BITS) - 2)
30 #define MANTISSA_BITS 12
31 #define MANTISSA_MAX ((1 << MANTISSA_BITS) - 1)
32 #define HIDDEN_BIT (1 << MANTISSA_BITS)
33 #define ONE_FLOAT ((float) (1 << (MANTISSA_BITS + 1)))
36 #if SIGN_BITS + EXPONENT_BITS + MANTISSA_BITS != 16
37 #error SIGN_BITS, EXPONENT_BITS and MANTISSA_BITS must sum to 16
40 sample_minifloat_t sample_from_float(float v)
45 sample_minifloat_t sign = 0;
50 // This check could conceivably be tighter: v < constexpr float_from_sample(1).
51 // Probably only useful to be made more accurate if this is changed to
52 // manipulate the raw IEEE single precision float bit fields.
54 // originally returned sign, but now seems better not to return negative 0
58 return SAMPLE_POS_MAX | sign;
61 float r = frexpf(v, &exp);
62 if ((exp += EXCESS) > EXPONENT_MAX) {
63 return SAMPLE_POS_MAX | sign;
65 if (-exp >= MANTISSA_BITS) {
66 // originally returned sign, but now seems better not to return negative 0
69 int mantissa = (int) (r * ONE_FLOAT);
70 sample_minifloat_t ret = exp > 0 ? (exp << MANTISSA_BITS) | (mantissa & ~HIDDEN_BIT) :
71 (mantissa >> (1 - exp)) & MANTISSA_MAX;
76 float float_from_sample(sample_minifloat_t a)
78 int mantissa = a & MANTISSA_MAX;
79 int exponent = (a >> MANTISSA_BITS) & EXPONENT_MAX;
80 float f = ldexpf((exponent > 0 ? HIDDEN_BIT | mantissa : mantissa << 1) / ONE_FLOAT,
82 return a & SIGN_MASK ? -f : f;