Previously, one-byte loads were typically done by reading a 16-bit value and then masking off the upper 8 bits. This is a problem when accessing softswitches or slot IO locations, because reading the subsequent byte may have some undesired effect. Now, ORCA/C will do an 8-bit read for such cases, if the volatile qualifier is used.
There were also a couple optimizations that could occasionally result in not all the bytes of a larger value actually being read. These are now disabled for volatile loads that may access softswitches or IO.
These changes should make ORCA/C more suitable for writing low-level software like device drivers.
This affects functions whose body spans multiple files due to includes, or is treated as doing so due to #line directives. ORCA/C will now generate a COP 6 instruction to record each source file change, allowing debuggers to properly track the flow of execution across files.
This makes it more likely that unsupported ops on long long or any other types added in the future will give an error rather than silently generating bad code.
Also, update a comment.
Per the C standards, the % operator should give a remainder after division, such that (a/b)*b + a%b equals a (provided that a/b is representable). As such, the operation of % is defined for cases where either or both of the operands are negative. Since division truncates toward 0, a%b should give a negative result (or 0) in cases where a is negative.
Previously, the % operator was essentially behaving like the "mod" operator in Pascal, which is equivalent for positive operands but not if either operand is negative. It would generally give incorrect results in those cases, or in some cases give compile-time or run-time errors.
This patch addresses both 16-bit and 32-bit signed computations at run time, and operations in constant expressions. The approach at run time is to call existing division routines, which return the correct remainder, except always as a positive number. The generated code checks the sign of the first operand, and if it is negative negates the remainder.
The code generated is somewhat large (especially for the 32-bit case), so it might be sensible to put it in a library function and call that, but for now it's just generated in-line. This avoids introducing a dependency on a new library function, so the generated code remains compatible with older versions of ORCALib (e.g. the GNO one).
Fixes#10.
