qapi: merge QInt and QFloat in QNum

We would like to use a same QObject type to represent numbers, whether
they are int, uint, or floats. Getters will allow some compatibility
between the various types if the number fits other representations.

Add a few more tests while at it.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20170607163635.17635-7-marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[parse_stats_intervals() simplified a bit, comment in
test_visitor_in_int_overflow() tidied up, suppress bogus warnings]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

qobject/qnum.c

@@ -0,0 +1,159 @@
+/*
+ * QNum Module
+ *
+ * Copyright (C) 2009 Red Hat Inc.
+ *
+ * Authors:
+ *  Luiz Capitulino <lcapitulino@redhat.com>
+ *  Anthony Liguori <aliguori@us.ibm.com>
+ *  Marc-André Lureau <marcandre.lureau@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
+ * See the COPYING.LIB file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "qapi/qmp/qnum.h"
+#include "qapi/qmp/qobject.h"
+#include "qemu-common.h"
+
+/**
+ * qnum_from_int(): Create a new QNum from an int64_t
+ *
+ * Return strong reference.
+ */
+QNum *qnum_from_int(int64_t value)
+{
+    QNum *qn = g_new(QNum, 1);
+
+    qobject_init(QOBJECT(qn), QTYPE_QNUM);
+    qn->kind = QNUM_I64;
+    qn->u.i64 = value;
+
+    return qn;
+}
+
+/**
+ * qnum_from_double(): Create a new QNum from a double
+ *
+ * Return strong reference.
+ */
+QNum *qnum_from_double(double value)
+{
+    QNum *qn = g_new(QNum, 1);
+
+    qobject_init(QOBJECT(qn), QTYPE_QNUM);
+    qn->kind = QNUM_DOUBLE;
+    qn->u.dbl = value;
+
+    return qn;
+}
+
+/**
+ * qnum_get_try_int(): Get an integer representation of the number
+ *
+ * Return true on success.
+ */
+bool qnum_get_try_int(const QNum *qn, int64_t *val)
+{
+    switch (qn->kind) {
+    case QNUM_I64:
+        *val = qn->u.i64;
+        return true;
+    case QNUM_DOUBLE:
+        return false;
+    }
+
+    assert(0);
+    return false;
+}
+
+/**
+ * qnum_get_int(): Get an integer representation of the number
+ *
+ * assert() on failure.
+ */
+int64_t qnum_get_int(const QNum *qn)
+{
+    int64_t val;
+    bool success = qnum_get_try_int(qn, &val);
+    assert(success);
+    return val;
+}
+
+/**
+ * qnum_get_double(): Get a float representation of the number
+ *
+ * qnum_get_double() loses precision for integers beyond 53 bits.
+ */
+double qnum_get_double(QNum *qn)
+{
+    switch (qn->kind) {
+    case QNUM_I64:
+        return qn->u.i64;
+    case QNUM_DOUBLE:
+        return qn->u.dbl;
+    }
+
+    assert(0);
+    return 0.0;
+}
+
+char *qnum_to_string(QNum *qn)
+{
+    char *buffer;
+    int len;
+
+    switch (qn->kind) {
+    case QNUM_I64:
+        return g_strdup_printf("%" PRId64, qn->u.i64);
+    case QNUM_DOUBLE:
+        /* FIXME: snprintf() is locale dependent; but JSON requires
+         * numbers to be formatted as if in the C locale. Dependence
+         * on C locale is a pervasive issue in QEMU. */
+        /* FIXME: This risks printing Inf or NaN, which are not valid
+         * JSON values. */
+        /* FIXME: the default precision of 6 for %f often causes
+         * rounding errors; we should be using DBL_DECIMAL_DIG (17),
+         * and only rounding to a shorter number if the result would
+         * still produce the same floating point value.  */
+        buffer = g_strdup_printf("%f" , qn->u.dbl);
+        len = strlen(buffer);
+        while (len > 0 && buffer[len - 1] == '0') {
+            len--;
+        }
+
+        if (len && buffer[len - 1] == '.') {
+            buffer[len - 1] = 0;
+        } else {
+            buffer[len] = 0;
+        }
+
+        return buffer;
+    }
+
+    assert(0);
+    return NULL;
+}
+
+/**
+ * qobject_to_qnum(): Convert a QObject into a QNum
+ */
+QNum *qobject_to_qnum(const QObject *obj)
+{
+    if (!obj || qobject_type(obj) != QTYPE_QNUM) {
+        return NULL;
+    }
+    return container_of(obj, QNum, base);
+}
+
+/**
+ * qnum_destroy_obj(): Free all memory allocated by a
+ * QNum object
+ */
+void qnum_destroy_obj(QObject *obj)
+{
+    assert(obj != NULL);
+    g_free(qobject_to_qnum(obj));
+}