[PATCH 1/3] Document max_align_t

[Paul Eggert]

* manual/lang.texi (Important Data Types): Mention max_align_t.
---
 manual/lang.texi | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/manual/lang.texi b/manual/lang.texi
index cd90ff60d2..b985cf4561 100644
--- a/manual/lang.texi
+++ b/manual/lang.texi
@@ -16,7 +16,7 @@ features has been written, we are publishing it here.
 * Variadic Functions::          Defining functions with varying numbers
                                  of args.
 * Null Pointer Constant::       The macro @code{NULL}.
-* Important Data Types::        Data types for object sizes.
+* Important Data Types::        Types for object sizes and alignments.
 * Data Type Measurements::      Parameters of data type representations.
 @end menu
 
@@ -555,7 +555,8 @@ recommend instead adding a prototype for the function you are calling.
 The result of subtracting two pointers in C is always an integer, but the
 precise data type varies from C compiler to C compiler.  Likewise, the
 data type of the result of @code{sizeof} also varies between compilers.
-ISO C defines standard aliases for these two types, so you can refer to
+Also, it is helpful to have a data type with the greatest standard alignment.
+ISO C defines standard aliases for these types, so you can refer to
 them in a portable fashion.  They are defined in the header file
 @file{stddef.h}.
 @pindex stddef.h
@@ -583,10 +584,24 @@ will be @w{@code{unsigned int}} or @w{@code{unsigned long int}}.
 arguments or variables that hold the size of an object.
 @end deftp
 
+@deftp {Data Type} max_align_t
+@standards{ISO, stddef.h}
+@cindex fundamental alignment
+This is an object type with the greatest @dfn{fundamental alignment},
+i.e., the greatest alignment of all integer, floating, enumerated,
+pointer, and standard library types such as @code{mbstate_t}, along
+with all array, structure, and union types that are composed only of
+these types and that lack stricter alignment specifiers.
+Code can use @code{alignof (max_align_t)} when calculating space
+needed for arbitrary collections of objects, so long as the objects'
+types are fundamental and lack stricter alignment specifiers.
+@end deftp
+
 @strong{Compatibility Note:} Implementations of C before the advent of
 @w{ISO C} generally used @code{unsigned int} for representing object sizes
 and @code{int} for pointer subtraction results.  They did not
-necessarily define either @code{size_t} or @code{ptrdiff_t}.  Unix
+necessarily have @code{<stddef.h>} or define the types @code{size_t},
+@code{ptrdiff_t}, or @code{max_align_t}.  Unix
 systems did define @code{size_t}, in @file{sys/types.h}, but the
 definition was usually a signed type.
 
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2.52.0