Re: [PATCH v3 1/4] Document max_align_t

[Florian Weimer <fweimer@redhat.com>]

* Paul Eggert:

> * manual/lang.texi (Important Data Types): Mention max_align_t.
> ---
>  manual/lang.texi | 28 ++++++++++++++++++++--------
>  1 file changed, 20 insertions(+), 8 deletions(-)
>
> diff --git a/manual/lang.texi b/manual/lang.texi
> index cd90ff60d2..28e7de2b2c 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 sizes and alignments of objects.
>  * 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 helps to have a data type with the greatest fundamental 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
> @@ -583,12 +584,23 @@ will be @w{@code{unsigned int}} or @w{@code{unsigned long int}}.
>  arguments or variables that hold the size of an object.
>  @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
> -systems did define @code{size_t}, in @file{sys/types.h}, but the
> -definition was usually a signed type.
> +@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 needed by standard types.
> +Code can use @code{alignof (max_align_t)} when calculating space
> +needed for arbitrary collections of objects, so long as the objects'
> +types have a fundamental alignment and lack stricter alignment specifiers.
> +@end deftp
> +
> +In @theglibc{}, the value of @code{alignof (max_align_t)} is 16 on
> +most architectures.  However, it is 8 on 32-bit architectures that do
> +not require 16-byte alignment from @code{malloc} to support predefined
> +types.
> +
> +@strong{Compatibility Note:} The C11 standard introduced @code{max_align_t};
> +older compilers may lack the type.

This version looks good to me.

Reviewed-by: Florian Weimer <fweimer@redhat.com>

Thanks,
Florian