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 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 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
