Signed/unsigned char on different platforms

[matthiasdiener]

I'm not sure how much difference it makes in practice, but the char type in C/C++ isn't guaranteed to be signed or unsigned.

By default, x86/M1 seem to treat char as signed, but ppc64le treats it as unsigned. This can also be modified by compiler options (e.g., https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/C-Dialect-Options.html#index-funsigned-char).

compyte/dtypes.py

Line 122 in d4549d4

reg.get_or_register_dtype(["signed char", "char"], np.int8)

OpenCL seems to define it as signed: https://registry.khronos.org/OpenCL/specs/3.0-unified/html/OpenCL_C.html#built-in-scalar-data-types

[inducer]

In terms of code generation, I believe it is the first item in the list that's relevant, i.e. an explicit signed char should be generated. The other items are for parsing string-ly arguments in pyopencl, where I think treating char as signed is a safe default if the user doesn't specify.