1/*
2 * Copyright (C) 2017 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 LIBTEXTCLASSIFIER_COMMON_FLOAT16_H_
18#define LIBTEXTCLASSIFIER_COMMON_FLOAT16_H_
19
20#include "util/base/casts.h"
21#include "util/base/integral_types.h"
22
23namespace libtextclassifier {
24namespace nlp_core {
25
26// 16 bit encoding of a float.  NOTE: can't be used directly for computation:
27// one first needs to convert it to a normal float, using Float16To32.
28//
29// Documentation copied from original file:
30//
31// Compact 16-bit encoding of floating point numbers. This
32// representation uses 1 bit for the sign, 8 bits for the exponent and
33// 7 bits for the mantissa.  It is assumed that floats are in IEEE 754
34// format so a float16 is just bits 16-31 of a single precision float.
35//
36// NOTE: The IEEE floating point standard defines a float16 format that
37// is different than this format (it has fewer bits of exponent and more
38// bits of mantissa).  We don't use that format here because conversion
39// to/from 32-bit floats is more complex for that format, and the
40// conversion for this format is very simple.
41//
42// <---------float16------------>
43// s e e e e e e e e f f f f f f f f f f f f f f f f f f f f f f f
44// <------------------------------float-------------------------->
45// 3 3             2 2             1 1                           0
46// 1 0             3 2             5 4                           0
47
48typedef uint16 float16;
49
50static inline float16 Float32To16(float f) {
51  // Note that we just truncate the mantissa bits: we make no effort to
52  // do any smarter rounding.
53  return (bit_cast<uint32>(f) >> 16) & 0xffff;
54}
55
56static inline float Float16To32(float16 f) {
57  // We fill in the new mantissa bits with 0, and don't do anything smarter.
58  return bit_cast<float>(f << 16);
59}
60
61}  // namespace nlp_core
62}  // namespace libtextclassifier
63
64#endif  // LIBTEXTCLASSIFIER_COMMON_FLOAT16_H_
65