HT-2021-000363 - [2025] EWHC 532 (TCC)

The IBM C language runtime contains functionality used to round floating point numbers (non-integers which contain a decimal point). Arithmetic and conversion operations performed by the mainframe produce an intermediate result correct to infinite precision and with unbounded range. Unless that intermediate result can be represented exactly in the target format, it is replaced by a value that depends on the rounding mode used. There are various rounding modes that can be used and the mathematical operations used to perform rounding are set out in a published standard of the Institute of Electrical and Electronics Engineers Inc, IEEE-754.

The IBM mainframe provides a floating point control register (“the FPC”) that enables users of the IBM C language runtime to specify the rounding mode to format the results of their calculations. The format of the FPC is published by IBM in publicly available documentation, namely, the IBM Principles of Operation manual.

In the IBM C language runtime, a data structure called “_FP_fpcreg_t” (“the FPC Data Structure”), is used to identify the rounding mode specified by the customer application, using IBM supplied APIs to view and modify the FPC accordingly. The functions of the APIs are set out in publicly available documentation.

The experts agree that the IBM XL C/C++ compiler provides a header file that provides C language source code that maps the FPC data area, which is made available to z/OS customers but which is not publicly documented in full. The z/OS language environment APIs take this data as input and provide it as output. The use of this structure is partially shown in IBM documentation but the internal code is not shown.

The allegation is that Winsopia used reverse engineering to test the APIs that modify the FPC, ascertain the effect of different values on the API rounding functions and determine how it performed number rounding.

On 17 February 2021 Peeter Joot of LzLabs created DR 520, requesting Winsopia to run test programs to discover the rounding mode selection data structure and the values corresponding to four floating point number functions. Subsequently further versions of the test programs were supplied to be run on the mainframe. Winsopia compiled and executed the programs and provided to LzLabs the program output, compiler listings and scrubbed load modules created.

On 18 February 2021 Mr Joot made a commit to the SDM source code, adding parameter structures for the SDM replacement FPC data structure, citing as the source of the change DR 520. On 1 March 2021 Mr Joot made a further commit, modifying one of the fields of the data structure, again citing DR 520 as the source.

The experts’ second joint statement contains the following agreed statements:

The disputed issues are:

IBM’s case is that the FPC Data Structure and the IBM supplied APIs are component parts of the IBM C Language runtime, part of z/OS v2 Base, an ICA Program.

The defendants’ case is that the information sent by Winsopia to LzLabs took the form of compiler listings and scrubbed load modules. This was interface information, comprising material output by the compiler and not an ICA Program.

Winsopia provided output data, printing out all the bytes contained in the requested configurations of the FPC Data Structure. As such, this amounted to reverse engineering of the C Language runtime, which was an ICA Program within the meaning of the ICA and a transfer outside Winsopia’s Enterprise.

The defendants’ case is that Winsopia’s actions amounted to permitted observation, study and testing of the interfaces that modify the FPC register, in particular, the format and values of the rounding mode selection data structures inserted by the IBM C compiler.

I reject that submission. Winsopia did not confine its actions to examining the input and output of the test programs to determine the functioning of the C language runtime. Winsopia’s production of the compiler listings disclosed, not just the output of the program but the data structures and how the C language runtime dealt with rounding modes or changes to rounding modes specified in customer applications, that is, expression of the program, rather than its functioning.

For the reasons set out above in respect of the compiler listings allegations, production of the compiler listings was not indispensable to obtain information necessary to achieve interoperability so as to engage the Article 6 exception.

Although it is common ground that Winsopia did not transfer to LzLabs any IBM source code or CSECTs, it did provide the values and configurations for the FPC Data Structure. This amounted to a transfer of an ICA Program in breach of clause 4.1.3(b) of the ICA.

It is common ground that LzLabs requested, and Winsopia supplied, the information required in DR 520 for development of the SDM by LzLabs. This was in breach of clauses 4.1 and 4.1.2(b) of the ICA.

In summary, on this issue: