164 lines
6.0 KiB
C++
164 lines
6.0 KiB
C++
/****************************************************************************
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**
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** Copyright (C) 2016 by Southwest Research Institute (R)
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** Copyright (C) 2019 Intel Corporation.
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** Contact: http://www.qt-project.org/legal
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**
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** This file is part of the QtCore module of the Qt Toolkit.
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**
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** $QT_BEGIN_LICENSE:LGPL$
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** Commercial License Usage
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** Licensees holding valid commercial Qt licenses may use this file in
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** accordance with the commercial license agreement provided with the
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** Software or, alternatively, in accordance with the terms contained in
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** a written agreement between you and The Qt Company. For licensing terms
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** and conditions see https://www.qt.io/terms-conditions. For further
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** information use the contact form at https://www.qt.io/contact-us.
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**
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** GNU Lesser General Public License Usage
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** Alternatively, this file may be used under the terms of the GNU Lesser
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** General Public License version 3 as published by the Free Software
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** Foundation and appearing in the file LICENSE.LGPL3 included in the
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** packaging of this file. Please review the following information to
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** ensure the GNU Lesser General Public License version 3 requirements
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** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
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**
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** GNU General Public License Usage
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** Alternatively, this file may be used under the terms of the GNU
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** General Public License version 2.0 or (at your option) the GNU General
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** Public license version 3 or any later version approved by the KDE Free
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** Qt Foundation. The licenses are as published by the Free Software
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** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
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** included in the packaging of this file. Please review the following
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** information to ensure the GNU General Public License requirements will
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** be met: https://www.gnu.org/licenses/gpl-2.0.html and
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** https://www.gnu.org/licenses/gpl-3.0.html.
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**
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** $QT_END_LICENSE$
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**
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****************************************************************************/
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#include <stdint.h>
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#include <stdio.h>
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/*
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* This tool generates the tables used by qfloat16 to implement a
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* software-emulated version of IEEE 754 binary16. qfloat16 automatically uses
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* CPU instructions to convert to and from float (IEEE 754 binary32), but if
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* the CPU is not guaranteed to have those instructions available at compile
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* time, then qfloat16 needs the tables to perform the conversion with
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* reasonable performance.
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*
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* Because Qt requires float to be IEEE 754 binary32, these tables are
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* platform-independent and will never change.
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*/
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uint32_t convertmantissa(int32_t i)
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{
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uint32_t m = i << 13; // Zero pad mantissa bits
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uint32_t e = 0; // Zero exponent
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while (!(m & 0x00800000)) { // While not normalized
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e -= 0x00800000; // Decrement exponent (1<<23)
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m <<= 1; // Shift mantissa
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}
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m &= ~0x00800000; // Clear leading 1 bit
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e += 0x38800000; // Adjust bias ((127-14)<<23)
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return m | e; // Return combined number
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}
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// we first build these tables up and then print them out as a separate step in order
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// to more closely map the implementation given in the paper.
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uint32_t basetable[512];
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uint32_t shifttable[512];
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int main()
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{
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uint32_t i;
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printf("/* This file was generated by util/qfloat16-tables/gen_qfloat16_tables.cpp */\n\n");
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printf("#include <QtCore/qfloat16.h>\n\n");
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printf("QT_BEGIN_NAMESPACE\n\n");
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printf("#if !defined(__ARM_FP16_FORMAT_IEEE)\n\n");
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printf("const quint32 qfloat16::mantissatable[2048] = {\n");
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printf("0,\n");
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for (i = 1; i < 1024; i++)
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printf("0x%XU,\n", convertmantissa(i));
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for (i = 1024; i < 2048; i++)
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printf("0x%XU,\n", 0x38000000U + ((i - 1024) << 13));
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printf("};\n\n");
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printf("const quint32 qfloat16::exponenttable[64] = {\n");
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printf("0,\n");
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for (i = 1; i < 31; i++)
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printf("0x%XU,\n", i << 23);
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printf("0x47800000U,\n"); // 31
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printf("0x80000000U,\n"); // 32
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for (i = 33; i < 63; i++)
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printf("0x%XU,\n", 0x80000000U + ((i - 32) << 23));
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printf("0xC7800000U,\n"); // 63
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printf("};\n\n");
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printf("const quint32 qfloat16::offsettable[64] = {\n");
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printf("0,\n");
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for (i = 1; i < 32; i++)
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printf("1024U,\n");
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printf("0,\n");
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for (i = 33; i < 64; i++)
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printf("1024U,\n");
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printf("};\n\n");
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int32_t e;
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for (i = 0; i < 256; ++i) {
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e = i - 127;
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if (e < -24) { // Very small numbers map to zero
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basetable[i | 0x000] = 0x0000;
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basetable[i | 0x100] = 0x8000;
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shifttable[i | 0x000] = 24;
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shifttable[i | 0x100] = 24;
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} else if (e < -14) { // Small numbers map to denorms
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basetable[i | 0x000] = (0x0400 >> (-e - 14));
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basetable[i | 0x100] = (0x0400 >> (-e - 14)) | 0x8000;
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shifttable[i | 0x000] = -e - 1;
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shifttable[i | 0x100] = -e - 1;
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} else if (e <= 15) { // Normal numbers just lose precision
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basetable[i | 0x000] = ((e + 15) << 10);
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basetable[i | 0x100] = ((e + 15) << 10) | 0x8000;
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shifttable[i | 0x000] = 13;
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shifttable[i | 0x100] = 13;
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} else if (e < 128) { // Large numbers map to Infinity
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basetable[i | 0x000] = 0x7C00;
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basetable[i | 0x100] = 0xFC00;
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shifttable[i | 0x000] = 24;
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shifttable[i | 0x100] = 24;
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} else { // Infinity and NaN's stay Infinity and NaN's
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basetable[i | 0x000] = 0x7C00;
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basetable[i | 0x100] = 0xFC00;
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shifttable[i | 0x000] = 13;
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shifttable[i | 0x100] = 13;
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}
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}
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printf("const quint32 qfloat16::basetable[512] = {\n");
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for (i = 0; i < 512; i++)
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printf("0x%XU,\n", basetable[i]);
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printf("};\n\n");
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printf("const quint32 qfloat16::shifttable[512] = {\n");
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for (i = 0; i < 512; i++)
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printf("0x%XU,\n", shifttable[i]);
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printf("};\n\n");
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printf("#endif // !__ARM_FP16_FORMAT_IEEE\n\n");
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printf("QT_END_NAMESPACE\n");
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return 0;
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}
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