Suggested-by: Max Reitz <mre...@redhat.com>
Signed-off-by: Markus Armbruster <arm...@redhat.com>
Message-Id: <1503384739-17207-1-git-send-email-arm...@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lur...@redhat.com>
[Comment typos fixed]
---
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 09d745c490..d6b0791139 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 as 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 fits 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;
--
2.13.5
