ak.forms.form.index_to_dtype is probably wrong: should probably be native, not little-endian

[jpivarski]

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awkward/src/awkward/types/numpytype.py

Lines 67 to 83 in fb245f1

	_primitive_to_dtype_dict = {
	"bool": np.dtype(np.bool_),
	"int8": np.dtype(np.int8),
	"uint8": np.dtype(np.uint8),
	"int16": np.dtype(np.int16),
	"uint16": np.dtype(np.uint16),
	"int32": np.dtype(np.int32),
	"uint32": np.dtype(np.uint32),
	"int64": np.dtype(np.int64),
	"uint64": np.dtype(np.uint64),
	"float32": np.dtype(np.float32),
	"float64": np.dtype(np.float64),
	"complex64": np.dtype(np.complex64),
	"complex128": np.dtype(np.complex128),
	"datetime64": np.dtype(np.datetime64),
	"timedelta64": np.dtype(np.timedelta64),
	}

which sets the dtype for each primitive category to the native-endianness for the machine (np.dtype(np.float64) will be big-endian on big-endian machines and little-endian on little-endian machines) with

awkward/src/awkward/forms/form.py

Lines 375 to 381 in 8285871

	index_to_dtype: Final[dict[str, DType]] = {
	"i8": np.dtype("<i1"),
	"u8": np.dtype("<u1"),
	"i32": np.dtype("<i4"),
	"u32": np.dtype("<u4"),
	"i64": np.dtype("<i8"),
	}

which sets the dtype for each index category to little-endian. This should probably be native-endian, too. I'm 90% sure of it.

The problem is that we'd like to test it before we change it. Is there any way we can test Awkward on a big-endian machine? Maybe in a qemu emulation? (Such a test would probably reveal a lot.)

On the flip side, the fact that it's so hard to find a big-endian machine these days means that this issue would rarely be observed. (Similar to 32-bit testing...)