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Re: [PATCH 0/3] yacc: compute the best type for the state number

From: Paul Eggert
Subject: Re: [PATCH 0/3] yacc: compute the best type for the state number
Date: Sat, 5 Oct 2019 18:58:40 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0

On 10/5/19 7:41 AM, Akim Demaille wrote:

Why have they chosen this?  I guess the point is speed.

Yes, typically these machines are not byte-addressable and it's faster to make every integer the same size. This is sort of the "BCPL variant" of C, which the C standard allows.

Maybe you want to extend the notes you added to NEWS.  Including
the bits about limits.h and stdint.h.  Maybe that should also make
its way into the doc, yet I wouldn't know where to write that.

OK, I did that in the revised patch (first attachment).

+typedef int yytype_uint8;

Wow!  Why do we fallback to int? Is this part where unsigned int == unsigned 
short == unsigned char on a little number of architecture?

Yes, it's for those odd platforms. Though I now see that the above was too extreme: it should have been 'short', not 'int'. Fixed in the first attached patch.
The medicine seems worse than the disease to me.

Well, let's use stronger medicine then :-). I did it in a different way in the first attached patch, so that yytype_uint8 should be 'unsigned char' except for the odd but valid platforms where unsigned char and/or unsigned short do not promote to int. On compilers not compatible with GCC, the revised patch includes <limits.h> and (if available) <stdint.h> which infringes on the user namespace, but yacc.c already infringes elsewhere for other reasons so that should be OK.

Eventually, all this should move up into c.m4, and be applied to
glr.c too.

Done in the second attached patch. (I haven't installed either patch yet.)

And see what to do about C++ parsers.

I was hoping our C++ expert could look into that....

Attachment: 0001-Use-least-types-for-integers-in-Yacc-tables.patch
Description: Text Data

Attachment: 0002-Move-the-integer-type-selection-into-c.m4.patch
Description: Text Data

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