diff options
author | Marc Mutz <marc.mutz@kdab.com> | 2012-05-18 20:12:35 +0200 |
---|---|---|
committer | The Qt Project <gerrit-noreply@qt-project.org> | 2013-04-03 11:38:35 +0200 |
commit | 76e0223619da02911d02813961ef631a5e02d826 (patch) | |
tree | 0fafdd9293508a89c7baed92b8d269dc93a36670 /src | |
parent | 6e7b8f79cb852ee1a6262a22aabd328b0e1b6dc0 (diff) |
Add qPopulationCount() function, extracted from QBitArray
This functionality is used in multiple places in Qt itself, so it makes
sense to have a global function for this. This also allows to map this
onto specialized assembler instructions, should an architecture provide
them, later on.
Also added comprehensive tests, using a 4-bit lookup-table implementation
as a reference.
Change-Id: I8c4ea72cce54506ebb9fbe61141dbb5f1b7a660f
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>
Diffstat (limited to 'src')
-rw-r--r-- | src/corelib/tools/qalgorithms.h | 38 | ||||
-rw-r--r-- | src/corelib/tools/qalgorithms.qdoc | 31 | ||||
-rw-r--r-- | src/corelib/tools/qbitarray.cpp | 11 | ||||
-rw-r--r-- | src/platformsupport/eglconvenience/qxlibeglintegration.cpp | 17 |
4 files changed, 75 insertions, 22 deletions
diff --git a/src/corelib/tools/qalgorithms.h b/src/corelib/tools/qalgorithms.h index e3b76886f1..2658cfc2c2 100644 --- a/src/corelib/tools/qalgorithms.h +++ b/src/corelib/tools/qalgorithms.h @@ -516,6 +516,44 @@ Q_OUTOFLINE_TEMPLATE RandomAccessIterator qBinaryFindHelper(RandomAccessIterator } //namespace QAlgorithmsPrivate +Q_DECL_CONSTEXPR inline uint qPopulationCount(quint32 v) +{ + // See http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel + return + (((v ) & 0xfff) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f + + (((v >> 12) & 0xfff) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f + + (((v >> 24) & 0xfff) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f; +} + +Q_DECL_CONSTEXPR inline uint qPopulationCount(quint8 v) +{ + return + (((v ) & 0xfff) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f; +} + +Q_DECL_CONSTEXPR inline uint qPopulationCount(quint16 v) +{ + return + (((v ) & 0xfff) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f + + (((v >> 12) & 0xfff) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f; +} + +Q_DECL_CONSTEXPR inline uint qPopulationCount(quint64 v) +{ + return + (((v ) & 0xfff) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f + + (((v >> 12) & 0xfff) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f + + (((v >> 24) & 0xfff) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f + + (((v >> 36) & 0xfff) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f + + (((v >> 48) & 0xfff) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f + + (((v >> 60) & 0xfff) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f; +} + +Q_DECL_CONSTEXPR inline uint qPopulationCount(long unsigned int v) +{ + return qPopulationCount(static_cast<quint64>(v)); +} + QT_END_NAMESPACE #endif // QALGORITHMS_H diff --git a/src/corelib/tools/qalgorithms.qdoc b/src/corelib/tools/qalgorithms.qdoc index cc544af868..7c3aa1a3b2 100644 --- a/src/corelib/tools/qalgorithms.qdoc +++ b/src/corelib/tools/qalgorithms.qdoc @@ -635,3 +635,34 @@ of \a value in the variable passed as a reference in argument \a n. \sa {qLess()}{qLess<T>()} */ + + +/*! + \fn uint qPopulationCount(quint8 v) + \relates <QtAlgorithms> + \since 5.2 + + Returns the number of bits set in \a v. This number also called + the Hamming Weight of \a v. + */ + +/*! + \fn uint qPopulationCount(quint16 v) + \relates <QtAlgorithms> + \since 5.2 + \overload + */ + +/*! + \fn uint qPopulationCount(quint32 v) + \relates <QtAlgorithms> + \since 5.2 + \overload + */ + +/*! + \fn uint qPopulationCount(quint64 v) + \relates <QtAlgorithms> + \since 5.2 + \overload + */ diff --git a/src/corelib/tools/qbitarray.cpp b/src/corelib/tools/qbitarray.cpp index 2b459b2b1b..4949476f25 100644 --- a/src/corelib/tools/qbitarray.cpp +++ b/src/corelib/tools/qbitarray.cpp @@ -40,6 +40,7 @@ ****************************************************************************/ #include "qbitarray.h" +#include <qalgorithms.h> #include <qdatastream.h> #include <qdebug.h> #include <string.h> @@ -159,24 +160,18 @@ int QBitArray::count(bool on) const for (int i = 0; i < len; ++i) numBits += testBit(i); #else - // See http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel const quint8 *bits = reinterpret_cast<const quint8 *>(d.data()) + 1; while (len >= 32) { quint32 v = quint32(bits[0]) | (quint32(bits[1]) << 8) | (quint32(bits[2]) << 16) | (quint32(bits[3]) << 24); - quint32 c = ((v & 0xfff) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f; - c += (((v & 0xfff000) >> 12) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f; - c += ((v >> 24) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f; len -= 32; bits += 4; - numBits += int(c); + numBits += int(qPopulationCount(v)); } while (len >= 24) { quint32 v = quint32(bits[0]) | (quint32(bits[1]) << 8) | (quint32(bits[2]) << 16); - quint32 c = ((v & 0xfff) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f; - c += (((v & 0xfff000) >> 12) * Q_UINT64_C(0x1001001001001) & Q_UINT64_C(0x84210842108421)) % 0x1f; len -= 24; bits += 3; - numBits += int(c); + numBits += int(qPopulationCount(v)); } while (len >= 0) { if (bits[len / 8] & (1 << ((len - 1) & 7))) diff --git a/src/platformsupport/eglconvenience/qxlibeglintegration.cpp b/src/platformsupport/eglconvenience/qxlibeglintegration.cpp index 58f24c0a04..80453816fc 100644 --- a/src/platformsupport/eglconvenience/qxlibeglintegration.cpp +++ b/src/platformsupport/eglconvenience/qxlibeglintegration.cpp @@ -41,17 +41,6 @@ #include "qxlibeglintegration_p.h" -static int countBits(unsigned long mask) -{ - int count = 0; - while (mask != 0) { - if (mask & 1) - ++count; - mask >>= 1; - } - return count; -} - VisualID QXlibEglIntegration::getCompatibleVisualId(Display *display, EGLDisplay eglDisplay, EGLConfig config) { VisualID visualId = 0; @@ -92,9 +81,9 @@ VisualID QXlibEglIntegration::getCompatibleVisualId(Display *display, EGLDisplay return visualId; } - int visualRedSize = countBits(chosenVisualInfo->red_mask); - int visualGreenSize = countBits(chosenVisualInfo->green_mask); - int visualBlueSize = countBits(chosenVisualInfo->blue_mask); + int visualRedSize = qPopulationCount(chosenVisualInfo->red_mask); + int visualGreenSize = qPopulationCount(chosenVisualInfo->green_mask); + int visualBlueSize = qPopulationCount(chosenVisualInfo->blue_mask); int visualAlphaSize = -1; // Need XRender to tell us the alpha channel size bool visualMatchesConfig = false; |