| /* |
| * 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; |
| } |