Add language about bit-fields (#743)

Add language about conversions to and from bit-fields.

Author: spall

specs/language/classes.tex

@@ -0,0 +1,20 @@
+\Ch{Classes}{Classes}
+\Sec{Bit-field}{Classes.Bitfield}
+\p A bit-field is a class member with an explicit size specified in bits. Bit-fields must be of an underflying integer type.
+\begin{HLSL}
+struct Foo {
+  uint A : 10;
+  bool B : 1;
+};
+\end{HLSL}
+\p A bit-field can be unnamed.  Unnamed bit-fields cannot be accessed or initialized.
+\begin{HLSL}
+struct Foo {
+  uint : 10;
+};
+\end{HLSL}
+\p The explicit size of a named bit-field must be a constant expression of integer type, and must resolve to a number greater than zero and less than or equal to the size of the specified type in bits.
+\p The explicit size of an unnamed bit-field can also be zero.
+\p A bit-field cannot be a static member.
+\Sec{Static Members}{Classes.Static}
+\Sec{Conversions}{Classes.Conversions}

specs/language/conversions.tex

@@ -31,6 +31,9 @@
 \p If the glvalue refers to an array of type \texttt{T}, the prvalue will refer
 to a copy of the array, not memory referred to by the glvalue.
 
+\p If the glvalue refers to a bit-field of type \texttt{T}, the conversion
+produces an object of the underlying type of the bit-field.
+
 \Sec{Array-to-pointer conversion}{Conv.array}
 
 \p An lvalue or rvalue of type \texttt{T[]} (unsized array), can be converted to
@@ -85,6 +88,12 @@
 \p If the source type is \texttt{bool}, the values \texttt{true} and
 \texttt{false} are converted to one and zero respectively.
 
+\Sec{Bit-field conversion}{Conv.bitfield}
+
+\p A glvalue of a named bit-field with underlying integer type \texttt{T} can be
+converted to a cxvalue of type \texttt{T$^\prime$} if there exists an implicit
+conversion from \texttt{T} to \texttt{T$^\prime$}.
+
 \Sec{Floating point conversion}{Conv.fconv}
 
 \p A glvalue of a floating point type can be converted to a cxvalue of any other

specs/language/placeholders.tex

@@ -4,9 +4,6 @@
 % forward references can be inserted into the specification as it is being
 % written to force updating the references as they change.
 
-\Ch{Classes}{Classes}
-\Sec{Static Members}{Classes.Static}
-\Sec{Conversions}{Classes.Conversions}
 \Ch{Templates}{Template}
 \Sec{Template Instantiation}{Template.Inst}
 \Sec{Partial Ordering of Function Templates}{Template.Func.Order}