You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
84 lines
2.6 KiB
84 lines
2.6 KiB
/*
|
|
* Copyright (C) 2014 The Android Open Source Project
|
|
*
|
|
* Licensed under the Apache License, Version 2.0 (the "License");
|
|
* you may not use this file except in compliance with the License.
|
|
* You may obtain a copy of the License at
|
|
*
|
|
* http://www.apache.org/licenses/LICENSE-2.0
|
|
*
|
|
* Unless required by applicable law or agreed to in writing, software
|
|
* distributed under the License is distributed on an "AS IS" BASIS,
|
|
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
* See the License for the specific language governing permissions and
|
|
* limitations under the License.
|
|
*/
|
|
|
|
#include <math.h>
|
|
#include <audio_utils/sample.h>
|
|
|
|
#define SAMPLE_NEG_MAX 0xFFFF
|
|
#define SAMPLE_POS_MAX 0x7FFF
|
|
|
|
#define SIGN_MASK 0x8000
|
|
#define SIGN_BITS 1
|
|
|
|
#define EXPONENT_BITS 3
|
|
#define EXPONENT_MAX ((1 << EXPONENT_BITS) - 1)
|
|
#define EXCESS ((1 << EXPONENT_BITS) - 2)
|
|
|
|
#define MANTISSA_BITS 12
|
|
#define MANTISSA_MAX ((1 << MANTISSA_BITS) - 1)
|
|
#define HIDDEN_BIT (1 << MANTISSA_BITS)
|
|
#define ONE_FLOAT ((float) (1 << (MANTISSA_BITS + 1)))
|
|
|
|
|
|
#if SIGN_BITS + EXPONENT_BITS + MANTISSA_BITS != 16
|
|
#error SIGN_BITS, EXPONENT_BITS and MANTISSA_BITS must sum to 16
|
|
#endif
|
|
|
|
sample_minifloat_t sample_from_float(float v)
|
|
{
|
|
if (isnan(v)) {
|
|
return 0;
|
|
}
|
|
sample_minifloat_t sign = 0;
|
|
if (v < 0.0f) {
|
|
sign = SIGN_MASK;
|
|
v = -v;
|
|
}
|
|
// This check could conceivably be tighter: v < constexpr float_from_sample(1).
|
|
// Probably only useful to be made more accurate if this is changed to
|
|
// manipulate the raw IEEE single precision float bit fields.
|
|
if (v <= 0.0f) {
|
|
// originally returned sign, but now seems better not to return negative 0
|
|
return 0;
|
|
}
|
|
if (v >= 2.0f) {
|
|
return SAMPLE_POS_MAX | sign;
|
|
}
|
|
int exp;
|
|
float r = frexpf(v, &exp);
|
|
if ((exp += EXCESS) > EXPONENT_MAX) {
|
|
return SAMPLE_POS_MAX | sign;
|
|
}
|
|
if (-exp >= MANTISSA_BITS) {
|
|
// originally returned sign, but now seems better not to return negative 0
|
|
return 0;
|
|
}
|
|
int mantissa = (int) (r * ONE_FLOAT);
|
|
sample_minifloat_t ret = exp > 0 ? (exp << MANTISSA_BITS) | (mantissa & ~HIDDEN_BIT) :
|
|
(mantissa >> (1 - exp)) & MANTISSA_MAX;
|
|
// ret != 0
|
|
return ret | sign;
|
|
}
|
|
|
|
float float_from_sample(sample_minifloat_t a)
|
|
{
|
|
int mantissa = a & MANTISSA_MAX;
|
|
int exponent = (a >> MANTISSA_BITS) & EXPONENT_MAX;
|
|
float f = ldexpf((exponent > 0 ? HIDDEN_BIT | mantissa : mantissa << 1) / ONE_FLOAT,
|
|
exponent - EXCESS);
|
|
return a & SIGN_MASK ? -f : f;
|
|
}
|