ISO/IEC TS 18661-1:2014 extends programming language C to support binary floating-point arithmetic conforming to ISO/IEC/IEEE 60559:2011. It covers all requirements of IEC 60559 as they pertain to C floating types that use IEC 60559 binary formats.
ISO/IEC TS 18661-1:2014 does not cover decimal floating-point arithmetic, nor does it cover most optional features of IEC 60559.
ISO/IEC TS 18661-1:2014 is primarily an update to IEC 9899:2011 (C11), normative Annex F (IEC 60559 floating-point arithmetic). However, it proposes that the new interfaces that are suitable for general implementations be added in the Library clauses of C11. Also it includes a few auxiliary changes in C11 where the specification is problematic for IEC 60559 support.