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Re: BITS_PER_UNIT less than 8
- From: rridge at csclub dot uwaterloo dot ca (Ross Ridge)
- To: gcc at gcc dot gnu dot org
- Date: Fri, 7 Dec 2007 15:37:26 -0500 (EST)
- Subject: Re: BITS_PER_UNIT less than 8
Boris Boesler writes:
> Ok, so what have I to do to write a back-end where all addresses are
> given in bits? Memory is addressed in bits, not bytes. So I set:
>
> #define BITS_PER_UNIT 1
> #define UNITS_PER_WORD 32
I don't know if it's useful to define the size of a byte to be less than
8-bits, even if that more accurately reflects the hardware. Standard C
requires that the char type both be at least 8 bits (UCHAR_MAX >= 256)
and the same size as a byte (sizeof(char) == 1). You can't define any
types that are smaller than a char and have sizeof work correctly.
>So, what can I do to get this running for my architecture?
If you think there's still some benefit from having GCC use a 1-bit byte,
you'll probably have to fix a number of assumptions made in the code.
Things like that the size of a byte is at least 8 bits and is the same
in frontend and backend.
Ross Ridge