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40
41#include "qfloat16.h"
42#include "private/qsimd_p.h"
43#include <cmath> // for fpclassify()'s return values
44
45QT_BEGIN_NAMESPACE
46
47/*!
48 \class qfloat16
49 \keyword 16-bit Floating Point Support
50 \ingroup funclists
51 \inmodule QtCore
52 \inheaderfile QFloat16
53 \brief Provides 16-bit floating point support.
54
55 The \c qfloat16 class provides support for half-precision (16-bit) floating
56 point data. It is fully compliant with IEEE 754 as a storage type. This
57 implies that any arithmetic operation on a \c qfloat16 instance results in
58 the value first being converted to a \c float. This conversion to and from
59 \c float is performed by hardware when possible, but on processors that do
60 not natively support half-precision, the conversion is performed through a
61 sequence of lookup table operations.
62
63 \c qfloat16 should be treated as if it were a POD (plain old data) type.
64 Consequently, none of the supported operations need any elaboration beyond
65 stating that it supports all arithmetic operators incident to floating point
66 types.
67
68 \note On x86 and x86-64 that to get hardware accelerated conversions you must
69 compile with F16C or AVX2 enabled, or use qFloatToFloat16() and qFloatFromFloat16()
70 which will detect F16C at runtime.
71
72 \since 5.9
73*/
74
75/*!
76 \macro QT_NO_FLOAT16_OPERATORS
77 \relates qfloat16
78 \since 5.12.4
79
80 Defining this macro disables the arithmetic operators for qfloat16.
81
82 This is only necessary on Visual Studio 2017 (and earlier) when including
83 \c {<QFloat16>} and \c{<bitset>} in the same translation unit, which would
84 otherwise cause a compilation error due to a toolchain bug (see
85 [QTBUG-72073]).
86*/
87
88/*!
89 \fn bool qIsInf(qfloat16 f)
90 \relates qfloat16
91
92 Returns true if the \c qfloat16 \a {f} is equivalent to infinity.
93
94 \sa qIsInf
95*/
96
97/*!
98 \fn bool qIsNaN(qfloat16 f)
99 \relates qfloat16
100
101 Returns true if the \c qfloat16 \a {f} is not a number (NaN).
102
103 \sa qIsNaN
104*/
105
106/*!
107 \fn bool qIsFinite(qfloat16 f)
108 \relates qfloat16
109
110 Returns true if the \c qfloat16 \a {f} is a finite number.
111
112 \sa qIsFinite
113*/
114
115/*!
116 \internal
117 \since 5.14
118 \fn bool qfloat16::isInf() const noexcept
119
120 Tests whether this \c qfloat16 value is an infinity.
121
122 \sa qIsInf()
123*/
124
125/*!
126 \internal
127 \since 5.14
128 \fn bool qfloat16::isNaN() const noexcept
129
130 Tests whether this \c qfloat16 value is "not a number".
131
132 \sa qIsNaN()
133*/
134
135/*!
136 \since 5.14
137 \fn bool qfloat16::isNormal() const noexcept
138
139 Returns \c true if this \c qfloat16 value is finite and in normal form.
140
141 \sa qFpClassify()
142*/
143
144/*!
145 \internal
146 \since 5.14
147 \fn bool qfloat16::isFinite() const noexcept
148
149 Tests whether this \c qfloat16 value is finite.
150
151 \sa qIsFinite()
152*/
153
154/*!
155 \since 5.15
156 \fn qfloat16 qfloat16::copySign(qfloat16 sign) const noexcept
157
158 Returns a qfloat16 with the sign of \a sign but the rest of its value taken
159 from this qfloat16. Serves as qfloat16's equivalent of std::copysign().
160*/
161
162/*!
163 \internal
164 \since 5.14
165 Implements qFpClassify() for qfloat16.
166
167 \sa qFpClassify()
168*/
169int qfloat16::fpClassify() const noexcept
170{
171 return isInf() ? FP_INFINITE : isNaN() ? FP_NAN
172 : !(b16 & 0x7fff) ? FP_ZERO : isNormal() ? FP_NORMAL : FP_SUBNORMAL;
173}
174
175/*! \fn int qRound(qfloat16 value)
176 \relates qfloat16
177
178 Rounds \a value to the nearest integer.
179
180 \sa qRound
181*/
182
183/*! \fn qint64 qRound64(qfloat16 value)
184 \relates qfloat16
185
186 Rounds \a value to the nearest 64-bit integer.
187
188 \sa qRound64
189*/
190
191/*! \fn bool qFuzzyCompare(qfloat16 p1, qfloat16 p2)
192 \relates qfloat16
193
194 Compares the floating point value \a p1 and \a p2 and
195 returns \c true if they are considered equal, otherwise \c false.
196
197 The two numbers are compared in a relative way, where the
198 exactness is stronger the smaller the numbers are.
199 */
200
201#if QT_COMPILER_SUPPORTS(F16C)
202static inline bool hasFastF16()
203{
204 // All processors with F16C also support AVX, but YMM registers
205 // might not be supported by the OS, or they might be disabled.
206 return qCpuHasFeature(F16C) && qCpuHasFeature(AVX);
207}
208
209extern "C" {
210#ifdef QFLOAT16_INCLUDE_FAST
211# define f16cextern static
212#else
213# define f16cextern extern
214#endif
215
216f16cextern void qFloatToFloat16_fast(quint16 *out, const float *in, qsizetype len) noexcept;
217f16cextern void qFloatFromFloat16_fast(float *out, const quint16 *in, qsizetype len) noexcept;
218
219#undef f16cextern
220}
221
222#elif defined(__ARM_FP16_FORMAT_IEEE) && defined(__ARM_NEON__) && (__ARM_FP & 2)
223static inline bool hasFastF16()
224{
225 return true;
226}
227
228static void qFloatToFloat16_fast(quint16 *out, const float *in, qsizetype len) noexcept
229{
230 __fp16 *out_f16 = reinterpret_cast<__fp16 *>(out);
231 qsizetype i = 0;
232 for (; i < len - 3; i += 4)
233 vst1_f16(out_f16 + i, vcvt_f16_f32(vld1q_f32(in + i)));
234 SIMD_EPILOGUE(i, len, 3)
235 out_f16[i] = __fp16(in[i]);
236}
237
238static void qFloatFromFloat16_fast(float *out, const quint16 *in, qsizetype len) noexcept
239{
240 const __fp16 *in_f16 = reinterpret_cast<const __fp16 *>(in);
241 qsizetype i = 0;
242 for (; i < len - 3; i += 4)
243 vst1q_f32(out + i, vcvt_f32_f16(vld1_f16(in_f16 + i)));
244 SIMD_EPILOGUE(i, len, 3)
245 out[i] = float(in_f16[i]);
246}
247#else
248static inline bool hasFastF16()
249{
250 return false;
251}
252
253static void qFloatToFloat16_fast(quint16 *, const float *, qsizetype) noexcept
254{
255 Q_UNREACHABLE();
256}
257
258static void qFloatFromFloat16_fast(float *, const quint16 *, qsizetype) noexcept
259{
260 Q_UNREACHABLE();
261}
262#endif
263/*!
264 \since 5.11
265 \relates qfloat16
266
267 Converts \a len floats from \a in to qfloat16 and stores them in \a out.
268 Both \a in and \a out must have \a len allocated entries.
269
270 This function is faster than converting values one by one, and will do runtime
271 F16C detection on x86 and x86-64 hardware.
272*/
273Q_CORE_EXPORT void qFloatToFloat16(qfloat16 *out, const float *in, qsizetype len) noexcept
274{
275 if (hasFastF16())
276 return qFloatToFloat16_fast(out: reinterpret_cast<quint16 *>(out), in, len);
277
278 for (qsizetype i = 0; i < len; ++i)
279 out[i] = qfloat16(in[i]);
280}
281
282/*!
283 \since 5.11
284 \relates qfloat16
285
286 Converts \a len qfloat16 from \a in to floats and stores them in \a out.
287 Both \a in and \a out must have \a len allocated entries.
288
289 This function is faster than converting values one by one, and will do runtime
290 F16C detection on x86 and x86-64 hardware.
291*/
292Q_CORE_EXPORT void qFloatFromFloat16(float *out, const qfloat16 *in, qsizetype len) noexcept
293{
294 if (hasFastF16())
295 return qFloatFromFloat16_fast(out, in: reinterpret_cast<const quint16 *>(in), len);
296
297 for (qsizetype i = 0; i < len; ++i)
298 out[i] = float(in[i]);
299}
300
301QT_END_NAMESPACE
302
303#include "qfloat16tables.cpp"
304#ifdef QFLOAT16_INCLUDE_FAST
305# include "qfloat16_f16c.c"
306#endif
307

source code of qtbase/src/corelib/global/qfloat16.cpp