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 #ifndef ANDROID_AUDIO_MINIFLOAT_H 18 #define ANDROID_AUDIO_MINIFLOAT_H 19 20 #include <stdint.h> 21 #include <sys/cdefs.h> 22 23 /** \cond */ 24 __BEGIN_DECLS 25 /** \endcond */ 26 27 /** A single gain expressed as minifloat */ 28 typedef uint16_t gain_minifloat_t; 29 30 /** A pair of gain_minifloat_t packed into a single word */ 31 typedef uint32_t gain_minifloat_packed_t; 32 33 /** The nominal range of a gain, expressed as a float */ 34 #define GAIN_FLOAT_ZERO 0.0f 35 #define GAIN_FLOAT_UNITY 1.0f 36 37 /** Unity gain expressed as a minifloat */ 38 #define GAIN_MINIFLOAT_UNITY 0xE000 39 40 /** Pack a pair of gain_mini_float_t into a combined gain_minifloat_packed_t */ 41 static inline gain_minifloat_packed_t gain_minifloat_pack(gain_minifloat_t left, 42 gain_minifloat_t right) 43 { 44 return (right << 16) | left; 45 } 46 47 /** Unpack a gain_minifloat_packed_t into the two gain_minifloat_t components */ 48 static inline gain_minifloat_t gain_minifloat_unpack_left(gain_minifloat_packed_t packed) 49 { 50 return packed & 0xFFFF; 51 } 52 53 static inline gain_minifloat_t gain_minifloat_unpack_right(gain_minifloat_packed_t packed) 54 { 55 return packed >> 16; 56 } 57 58 /** A pair of unity gains expressed as a gain_minifloat_packed_t */ 59 #define GAIN_MINIFLOAT_PACKED_UNITY gain_minifloat_pack(GAIN_MINIFLOAT_UNITY, GAIN_MINIFLOAT_UNITY) 60 61 /** 62 * Convert a float to the internal representation used for gains. 63 * The nominal range [0.0, 1.0], but the hard range is [0.0, 2.0). 64 * Negative and underflow values are converted to 0.0, 65 * and values larger than the hard maximum are truncated to the hard maximum. 66 * 67 * Minifloats are ordered, and standard comparisons may be used between them 68 * in the gain_minifloat_t representation. 69 * 70 * Details on internal representation of gains, based on mini-floats: 71 * The nominal maximum is 1.0 and the hard maximum is 1 ULP less than 2.0, or +6 dB. 72 * The minimum non-zero value is approximately 1.9e-6 or -114 dB. 73 * Negative numbers, infinity, and NaN are not supported. 74 * There are 13 significand bits specified, 1 implied hidden bit, 3 exponent bits, 75 * and no sign bit. Denormals are supported. 76 */ 77 gain_minifloat_t gain_from_float(float f); 78 79 /** Convert the internal representation used for gains to float */ 80 float float_from_gain(gain_minifloat_t gain); 81 82 /** \cond */ 83 __END_DECLS 84 /** \endcond */ 85 86 #endif // ANDROID_AUDIO_MINIFLOAT_H 87
