javascript - Why is creating a Float32Array with an offset that isn't a multiple of the element size not allowed?

Question

I'd like to read a binary file with a few 32 bit float values at byte offset 31.

Unfortunately, new Float32Array(buffer, 31, 6); does not work. An offset of 32 instead of 31 works but I need 31.

According to this page, offset has to be a multiple of the element size, 4 in this case.

I'm interested in the reason behind this behaviour. Why does it matter where the view starts?

The best workaround I found thus far has not made it into gecko yet so I can't use it.

Do I realy have to cut and copy the byte values into a new array to get my float values?

Answer 1

I'm interested in the reason behind this behaviour. Why does it matter where the view starts?

Some architectures do not allow unaligned word accesses, and there are performance penalties on architectures that do allow it such as x86 (though some instructions must be aligned).

Do I really have to cut and copy the byte values into a new array to get my float values?

Yes, just like Markus' example you should create a new ArrayBuffer with a UInt8Array view and a Float32Array view for a read_buffer (copy with UInt8Array view and interpret from Float32Array view). Then you can read from your data with a UInt8Array, copy that into your read_buffer view and then interpret using the Float32Array. It's quite a seamless process.