ERROR (due to Roundoff, etc.)
Below 0.97 ulps. Consequently hypot "5.0" "12.0" = 13.0 exactly; in general, hypot and cabs return an integer whenever an integer might be expected.
The same cannot be said for the shorter and faster version of hypot and cabs that is provided in the comments in cabs.c; its error can exceed 1.2 ulps.
As might be expected, hypot "v" "NaN" and hypot "NaN" "v" are NaN for all finite v. But programmers might be surprised at first to discover that hypot "±oo" "NaN" = +oo. This is intentional; it happens because hypot "oo" "v" = +oo for all v, finite or infinite. Hence hypot "oo" "v" is independent of v. Unlike the reserved operand fault on a VAX, the IEEE NaN is designed to disappear when it turns out to be irrelevant, as it does in hypot "oo" "NaN".