Re: [Qemu-devel] [PATCH] qobject: Explain how QNum works, and why

["Marc-André Lureau" <marcandre.lureau@redhat.com>]

----- Original Message -----
> Suggested-by: Max Reitz <mreitz@redhat.com>
> Signed-off-by: Markus Armbruster <armbru@redhat.com>

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>


> ---
>  include/qapi/qmp/qnum.h | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/include/qapi/qmp/qnum.h b/include/qapi/qmp/qnum.h
> index 09d745c..9182129 100644
> --- a/include/qapi/qmp/qnum.h
> +++ b/include/qapi/qmp/qnum.h
> @@ -23,6 +23,27 @@ typedef enum {
>      QNUM_DOUBLE
>  } QNumKind;
>  
> +/*
> + * QNum encapsulates how our dialect of JSON fills in the blanks left
> + * by the JSON specification (RFC 7159) regarding numbers.
> + *
> + * Conceptually, we treat number as an abstract type with three
> + * concrete subtypes: floating-point, signed integer, unsigned
> + * integer.  QNum implements this a discriminated union of double,
> + * int64_t, uint64_t.
> + *
> + * The JSON parser picks the subtype as follows.  If the number has a
> + * decimal point or an exponent, it is floating-point.  Else if it
> + * fits into int64_t, it's signed integer.  Else if it first into
> + * uint64_t, it's unsigned integer.  Else it's floating-point.
> + *
> + * Any number can serve as double: qnum_get_double() converts under
> + * the hood.
> + *
> + * An integer can serve as signed / unsigned integer as long as it is
> + * in range: qnum_get_try_int() / qnum_get_try_uint() check range and
> + * convert under the hood.
> + */
>  typedef struct QNum {
>      QObject base;
>      QNumKind kind;
> --
> 2.7.5
> 
>