add static QChar::is(High|Low)Surrogate methods

to avoid recoding of character

this also adds QChar::requiresSurrogates() static member
supposed to save from common mistake like `ucs4 > 0x10000`

Merge-request: 606
Reviewed-by: Thiago Macieira <thiago.macieira@nokia.com>

2 files changed, 38 insertions, 2 deletions

diff --git a/src/corelib/tools/qchar.cpp b/src/corelib/tools/qchar.cpp
index 67ea00d..2f09b0e 100644
--- a/src/corelib/tools/qchar.cpp
+++ b/src/corelib/tools/qchar.cpp
@@ -653,14 +653,41 @@ bool QChar::isSymbol() const
     \fn bool QChar::isHighSurrogate() const
 
     Returns true if the QChar is the high part of a utf16 surrogate
-    (ie. if its code point is between 0xd800 and 0xdbff).
+    (ie. if its code point is between 0xd800 and 0xdbff, inclusive).
 */
 
 /*!
     \fn bool QChar::isLowSurrogate() const
 
     Returns true if the QChar is the low part of a utf16 surrogate
-    (ie. if its code point is between 0xdc00 and 0xdfff).
+    (ie. if its code point is between 0xdc00 and 0xdfff, inclusive).
+*/
+
+/*!
+    \fn static bool QChar::isHighSurrogate(uint ucs4)
+    \since 4.7
+
+    Returns true if the UCS-4-encoded character specified by \a ucs4
+    is the high part of a utf16 surrogate
+    (ie. if its code point is between 0xd800 and 0xdbff, inclusive).
+*/
+
+/*!
+    \fn static bool QChar::isLowSurrogate(uint ucs4)
+    \since 4.7
+
+    Returns true if the UCS-4-encoded character specified by \a ucs4
+    is the high part of a utf16 surrogate
+    (ie. if its code point is between 0xdc00 and 0xdfff, inclusive).
+*/
+
+/*!
+    \fn static bool QChar::requiresSurrogates(uint ucs4)
+    \since 4.7
+
+    Returns true if the UCS-4-encoded character specified by \a ucs4
+    can be splited to the high and low parts of a utf16 surrogate
+    (ie. if its code point is greater than or equals to 0x10000).
 */
 
 /*!
diff --git a/src/corelib/tools/qchar.h b/src/corelib/tools/qchar.h
index 1432c7f..205f911 100644
--- a/src/corelib/tools/qchar.h
+++ b/src/corelib/tools/qchar.h
@@ -285,6 +285,15 @@ public:
     inline void setCell(uchar cell);
     inline void setRow(uchar row);
 
+    static inline bool isHighSurrogate(uint ucs4) {
+        return ((ucs4 & 0xfffffc00) == 0xd800);
+    }
+    static inline bool isLowSurrogate(uint ucs4) {
+        return ((ucs4 & 0xfffffc00) == 0xdc00);
+    }
+    static inline bool requiresSurrogates(uint ucs4) {
+        return (ucs4 >= 0x10000);
+    }
     static inline uint surrogateToUcs4(ushort high, ushort low) {
         return (uint(high)<<10) + low - 0x35fdc00;
     }