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Re: [patch 1/4] change specific int128 -> generic intN


> And the hardware really loads 20 bits and not 24 bits?  If so, I
> think you might want to consider changing the unit to 4 bits instead
> of 8 bits.  If no, the mode is padded and has 24-bit size so why is
> setting TYPE_PRECISION to 20 not sufficient to achieve what you
> want?

The hardware transfers data in and out of byte-oriented memory in
TYPE_SIZE_UNITS chunks.  Once in a hardware register, all operations
are either 8, 16, or 20 bits (TYPE_SIZE) in size.  So yes, values are
padded in memory, but no, they are not padded in registers.

Setting TYPE_PRECISION is mostly useless, because most of gcc assumes
it's the same as TYPE_SIZE and ignores it.  Heck, most of gcc is
oblivious to the idea that types might not be powers-of-two in size.
GCC doesn't even bother with a DECL_PRECISION.

> > Thus, in these cases, TYPE_SIZE and TYPE_SIZE_UNIT no longer have
> > a "* BITS_PER_UNIT" mathematical relationship.
> 
> I'm skeptical this can work, it's pretty fundamental.

It seems to work just fine in testing, and I'm trying to make it
non-fundamental.


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