New qfloat16 class

This constitutes a fairly complete submission of an entirely new
floating point type which conforms to IEEE 754 as a 16-bit storage
class.  Conversion between qfloat16 and float is currently performed
through a sequence of lookup tables.  Global-level functions
qRound(), qRound64(), qFuzzyCompare(), qFuzzyIsNull(), and
qIsNull() each with a qfloat16 parameter have been included
for completeness.

[ChangeLog][QtCore] Added new qfloat16 class.

Change-Id: Ia52eb27846965c14f8140c00faf5ba33c9443976
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 170 insertions, 0 deletions

diff --git a/src/tools/qfloat16-tables/gen_qfloat16_tables.cpp b/src/tools/qfloat16-tables/gen_qfloat16_tables.cpp
new file mode 100644
index 0000000000..f5051e25fc
--- /dev/null
+++ b/src/tools/qfloat16-tables/gen_qfloat16_tables.cpp
@@ -0,0 +1,161 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 by Southwest Research Institute (R)
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <qfile.h>
+#include <qdebug.h>
+
+quint32 convertmantissa(qint32 i)
+{
+    quint32 m = i << 13; // Zero pad mantissa bits
+    quint32 e = 0; // Zero exponent
+
+    while (!(m & 0x00800000)) {   // While not normalized
+        e -= 0x00800000;     // Decrement exponent (1<<23)
+        m <<= 1;             // Shift mantissa
+    }
+    m &= ~0x00800000;          // Clear leading 1 bit
+    e += 0x38800000;           // Adjust bias ((127-14)<<23)
+    return m | e;            // Return combined number
+}
+
+// we first build these tables up and then print them out as a separate step in order
+// to more closely map the implementation given in the paper.
+quint32 basetable[512];
+quint32 shifttable[512];
+
+#define PRINTHEX(a) "0x" + QByteArray::number(a,16).toUpper() + "U,\n"
+
+qint32 main(qint32 argc, char **argv)
+{
+    if (argc < 2) {
+        qWarning() << "Must provide output filename as argument.";
+        return -1;
+    }
+
+    QFile fid(argv[1]);
+    if (!fid.open(QIODevice::WriteOnly | QIODevice::Text)) {
+        qWarning() << "Abort: Failed to open/create file" << fid.fileName();
+        return -1;
+    }
+    quint32 i;
+
+    fid.write("/* This file was generated by gen_qfloat16_tables.cpp */\n\n");
+    fid.write("#include <QtCore/qfloat16.h>\n\n");
+
+    fid.write("QT_BEGIN_NAMESPACE\n\n");
+
+    fid.write("const quint32 qfloat16::mantissatable[2048] = {\n");
+    fid.write("0,\n");
+    for (i = 1; i < 1024; i++)
+        fid.write(PRINTHEX(convertmantissa(i)));
+    for (i = 1024; i < 2048; i++)
+        fid.write(PRINTHEX(0x38000000U + ((i - 1024) << 13)));
+    fid.write("};\n\n");
+
+    fid.write("const quint32 qfloat16::exponenttable[64] = {\n");
+    fid.write("0,\n");
+    for (i = 1; i < 31; i++)
+        fid.write(PRINTHEX(i << 23));
+    fid.write("0x47800000U,\n");  // 31
+    fid.write("0x80000000U,\n");  // 32
+    for (i = 33; i < 63; i++)
+        fid.write(PRINTHEX(0x80000000U + ((i - 32) << 23)));
+    fid.write("0xC7800000U,\n");  // 63
+    fid.write("};\n\n");
+
+    fid.write("const quint32 qfloat16::offsettable[64] = {\n");
+    fid.write("0,\n");
+    for (i = 1; i < 32; i++)
+        fid.write("1024U,\n");
+    fid.write("0,\n");
+    for (i = 33; i < 64; i++)
+        fid.write("1024U,\n");
+    fid.write("};\n\n");
+
+    qint32 e;
+    for (i = 0; i < 256; ++i) {
+        e = i - 127;
+        if (e < -24) {   // Very small numbers map to zero
+            basetable[i | 0x000] = 0x0000;
+            basetable[i | 0x100] = 0x8000;
+            shifttable[i | 0x000] = 24;
+            shifttable[i | 0x100] = 24;
+
+        } else if (e < -14) {             // Small numbers map to denorms
+            basetable[i | 0x000] = (0x0400 >> (-e - 14));
+            basetable[i | 0x100] = (0x0400 >> (-e - 14)) | 0x8000;
+            shifttable[i | 0x000] = -e - 1;
+            shifttable[i | 0x100] = -e - 1;
+
+        } else if (e <= 15) {            // Normal numbers just lose precision
+            basetable[i | 0x000] = ((e + 15) << 10);
+            basetable[i | 0x100] = ((e + 15) << 10) | 0x8000;
+            shifttable[i | 0x000] = 13;
+            shifttable[i | 0x100] = 13;
+
+        } else if (e < 128) {            // Large numbers map to Infinity
+            basetable[i | 0x000] = 0x7C00;
+            basetable[i | 0x100] = 0xFC00;
+            shifttable[i | 0x000] = 24;
+            shifttable[i | 0x100] = 24;
+
+        } else {                     // Infinity and NaN's stay Infinity and NaN's
+            basetable[i | 0x000] = 0x7C00;
+            basetable[i | 0x100] = 0xFC00;
+            shifttable[i | 0x000] = 13;
+            shifttable[i | 0x100] = 13;
+        }
+    }
+
+    fid.write("const quint32 qfloat16::basetable[512] = {\n");
+    for (i = 0; i < 512; i++)
+        fid.write(PRINTHEX(basetable[i]));
+
+    fid.write("};\n\n");
+
+    fid.write("const quint32 qfloat16::shifttable[512] = {\n");
+    for (i = 0; i < 512; i++)
+        fid.write(PRINTHEX(shifttable[i]));
+
+    fid.write("};\n\n");
+
+    fid.write("QT_END_NAMESPACE\n");
+    fid.close();
+    return 0;
+}
diff --git a/src/tools/qfloat16-tables/qfloat16-tables.pro b/src/tools/qfloat16-tables/qfloat16-tables.pro
new file mode 100644
index 0000000000..a7d10ac197
--- /dev/null
+++ b/src/tools/qfloat16-tables/qfloat16-tables.pro
@@ -0,0 +1,9 @@
+option(host_build)
+
+CONFIG += force_bootstrap
+SOURCES += gen_qfloat16_tables.cpp
+
+load(qt_tool)
+
+lib.CONFIG = dummy_install
+INSTALLS = lib