Reimplement qt_inf/qt_snan/qt_qnan using std::numeric_limits.

Qt already assumes a working IEEE-754 implementation, so we can rely
on a working std::numeric_limits<double>.

This patch also gets rid of three cases of type-punning with unions
(which is undefined behavior in C++).

Change-Id: Ic3747f49d55e372960abf2091c1d5752c1eccdff
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 14 insertions, 70 deletions

diff --git a/src/corelib/global/qnumeric_p.h b/src/corelib/global/qnumeric_p.h
index b56cdef939..650c32d44b 100644
--- a/src/corelib/global/qnumeric_p.h
+++ b/src/corelib/global/qnumeric_p.h
@@ -107,85 +107,29 @@ static inline bool isfinite(float f) { return std::isfinite(f); }
 #endif
 }
 
-#if !defined(Q_CC_MIPS)
-
-static const union { unsigned char c[8]; double d; } qt_be_inf_bytes = { { 0x7f, 0xf0, 0, 0, 0, 0, 0, 0 } };
-static const union { unsigned char c[8]; double d; } qt_le_inf_bytes = { { 0, 0, 0, 0, 0, 0, 0xf0, 0x7f } };
-static inline double qt_inf()
-{
-    return (QSysInfo::ByteOrder == QSysInfo::BigEndian
-            ? qt_be_inf_bytes.d
-            : qt_le_inf_bytes.d);
-}
-
-// Signaling NAN
-static const union { unsigned char c[8]; double d; } qt_be_snan_bytes = { { 0x7f, 0xf8, 0, 0, 0, 0, 0, 0 } };
-static const union { unsigned char c[8]; double d; } qt_le_snan_bytes = { { 0, 0, 0, 0, 0, 0, 0xf8, 0x7f } };
-static inline double qt_snan()
+Q_DECL_CONSTEXPR static inline double qt_inf() Q_DECL_NOEXCEPT
 {
-    return (QSysInfo::ByteOrder == QSysInfo::BigEndian
-            ? qt_be_snan_bytes.d
-            : qt_le_snan_bytes.d);
+    Q_STATIC_ASSERT_X(std::numeric_limits<double>::has_infinity,
+                      "platform has no definition for infinity for type double");
+    return std::numeric_limits<double>::infinity();
 }
 
-// Quiet NAN
-static const union { unsigned char c[8]; double d; } qt_be_qnan_bytes = { { 0xff, 0xf8, 0, 0, 0, 0, 0, 0 } };
-static const union { unsigned char c[8]; double d; } qt_le_qnan_bytes = { { 0, 0, 0, 0, 0, 0, 0xf8, 0xff } };
-static inline double qt_qnan()
+// Signaling NaN
+Q_DECL_CONSTEXPR static inline double qt_snan() Q_DECL_NOEXCEPT
 {
-    return (QSysInfo::ByteOrder == QSysInfo::BigEndian
-            ? qt_be_qnan_bytes.d
-            : qt_le_qnan_bytes.d);
+    Q_STATIC_ASSERT_X(std::numeric_limits<double>::has_signaling_NaN,
+                      "platform has no definition for signaling NaN for type double");
+    return std::numeric_limits<double>::signaling_NaN();
 }
 
-#else // Q_CC_MIPS
-
-static const unsigned char qt_be_inf_bytes[] = { 0x7f, 0xf0, 0, 0, 0, 0, 0, 0 };
-static const unsigned char qt_le_inf_bytes[] = { 0, 0, 0, 0, 0, 0, 0xf0, 0x7f };
-static inline double qt_inf()
+// Quiet NaN
+Q_DECL_CONSTEXPR static inline double qt_qnan() Q_DECL_NOEXCEPT
 {
-    const unsigned char *bytes;
-    bytes = (QSysInfo::ByteOrder == QSysInfo::BigEndian
-             ? qt_be_inf_bytes
-             : qt_le_inf_bytes);
-
-    union { unsigned char c[8]; double d; } returnValue;
-    memcpy(returnValue.c, bytes, sizeof(returnValue.c));
-    return returnValue.d;
+    Q_STATIC_ASSERT_X(std::numeric_limits<double>::has_quiet_NaN,
+                      "platform has no definition for quiet NaN for type double");
+    return std::numeric_limits<double>::quiet_NaN();
 }
 
-// Signaling NAN
-static const unsigned char qt_be_snan_bytes[] = { 0x7f, 0xf8, 0, 0, 0, 0, 0, 0 };
-static const unsigned char qt_le_snan_bytes[] = { 0, 0, 0, 0, 0, 0, 0xf8, 0x7f };
-static inline double qt_snan()
-{
-    const unsigned char *bytes;
-    bytes = (QSysInfo::ByteOrder == QSysInfo::BigEndian
-             ? qt_be_snan_bytes
-             : qt_le_snan_bytes);
-
-    union { unsigned char c[8]; double d; } returnValue;
-    memcpy(returnValue.c, bytes, sizeof(returnValue.c));
-    return returnValue.d;
-}
-
-// Quiet NAN
-static const unsigned char qt_be_qnan_bytes[] = { 0xff, 0xf8, 0, 0, 0, 0, 0, 0 };
-static const unsigned char qt_le_qnan_bytes[] = { 0, 0, 0, 0, 0, 0, 0xf8, 0xff };
-static inline double qt_qnan()
-{
-    const unsigned char *bytes;
-    bytes = (QSysInfo::ByteOrder == QSysInfo::BigEndian
-             ? qt_be_qnan_bytes
-             : qt_le_qnan_bytes);
-
-    union { unsigned char c[8]; double d; } returnValue;
-    memcpy(returnValue.c, bytes, sizeof(returnValue.c));
-    return returnValue.d;
-}
-
-#endif // Q_CC_MIPS
-
 static inline bool qt_is_inf(double d)
 {
     return qnumeric_std_wrapper::isinf(d);