internal: Add helper macro for checking multiply and add overflows

The macro does the two checks together so that it's obvious what we're
checking as doing it in place is really unpleasant.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>

diff --git a/src/internal.h b/src/internal.h
index 01860efad9e968d108155cb1ebd3035a74b28933..20aa9b1d418982fdffddd1da9864c312d33e8c5e 100644 (file)
--- a/src/internal.h
+++ b/src/internal.h
@@ -43,6 +43,17 @@
 
 #define VIR_INT_MULTIPLY_OVERFLOW(a,b) (G_UNLIKELY ((b) > 0 && (a) > G_MAXINT / (b)))
 
+/**
+ * VIR_MULTIPLY_ADD_IS_OVERFLOW:
+ * @limit: maximum value of data type
+ * @value: current value
+ * @multiply: number @value is going to be multiplied by
+ * @add: number that will be added to @value after multiplication
+ */
+#define VIR_MULTIPLY_ADD_IS_OVERFLOW(limit, value, multiply, add) \
+  (G_UNLIKELY(((multiply) > 0 && (value) > (limit) / (multiply)) || \
+              ((limit) - ((value) * (multiply)) < (add))))
+
 /* The library itself is allowed to use deprecated functions /
  * variables, so effectively undefine the deprecated attribute
  * which would otherwise be defined in libvirt.h.