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Converting SPL to HP C/XL SPL is a procedure-oriented language. The basic structure of SPL and most of the language constructs are machine-independent. However, machine-dependent constructs are embedded within SPL to allow systems programmers to optimize programs and access system-specific hardware features. The C language is a portable, machine-independent programming language. Like SPL, C is a procedure-oriented language that uses many similar constructs. This similarity, while making C a good candidate for converting SPL programs, initially may cause some difficulties for experienced SPL programmers. For example: C uses "=" as the assignment operator; SPL uses ":="; C uses "==" as the equality operator; SPL uses "=". HP C/XL is the Hewlett-Packard implementation of C on MPE XL machines. HP C/XL is a highly portable version of the C language. SPL programs that rarely use machine-dependent constructs are easy to translate to HP C/XL. Consequently, the first step in any SPL to HP C/XL conversion is to isolate, and, if possible, eliminate the use of machine-dependent SPL features. Machine-dependent SPL features include direct reference to hardware registers, assembly instructions, and explicit stack manipulation. Many of these operations are used to optimize the MPE V environment and can be easily rewritten in higher level SPL constructs that can be converted directly to HP C/XL. Machine-dependent SPL features allow access to extra data segments to overcome the limited address space on MPE V machines. This restriction is not present in MPE XL, so these routines may be simplified or eliminated. Such changes can be made (but not tested) in the MPE V environment. SPL programs sometimes rely upon the hardware stack environment of MPE V machines. MPE XL machines do not have hardware stacks. Although you could emulate a stack in software, using HP C/XL constructs and data structures, usually the better choice is to redesign the algorithm and rewrite the affected program. Some high-level SPL constructs can be rewritten using alternative SPL operations that are easier to translate into HP C/XL. For example, SPL allows subroutines to be local to procedures. Although HP C/XL does allow nested blocks (compound statements with local data), HP C/XL does not allow any nesting of functions. Rewriting an SPL program to eliminate subroutines, either by placing the code inline, or by converting the SPL subroutine into an SPL procedure, will allow direct translation of the program structure into HP C/XL.