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Date: Sun, 13 Nov 2011 14:49:14 -0800
From: Bakul Shah <usenet@bitblocks.com>
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Subject: Re: big-little
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On 11/13/11 12:40 PM, Chris Gray wrote:
> BGB<cr88192@hotmail.com>  writes:
>
>> mine is plain C, so no GCC'isms here.
>> my stuff builds with both GCC and MSVC, with me using MSVC as the main
>> compiler when building on Windows.
>
> Conditional compilation:
>
>      #ifdef __GNUC__
>      #define USE_COMPUTED_GOTO	1
>      #else
>      #define USE_COMPUTED_GOTO	0
>      #endif
>
> plus some macros "CASE" and "BREAK" to do the right things.
>

This brings back some happy hacking memories! From some very old code:
[IIRC on a 33Mhz 386 the simulator was faster than the real 2Mhz 8bitter]

#define DO1(op, arg, ticks) { \
         Byte vb; Word vw; Byte* a; \
         COUNT += ticks; if (COUNT >= cpu->trigger) INTR |= ITIME; \
         arg; op; \
         NEXT; \
}

#define DO(op, ticks) DO1(op, 0, ticks)

#       if __GNUC__ > 1 && defined DIRECT_JUMP
         static const void * const caselab[256] = {
                 &&x00, &&x01, &&x02, &&x03, &&x04, &&x05, &&x06, &&x07,
                 &&x08, &&x09, &&x0a, &&x0b, &&x0c, &&x0d, &&x0e, &&x0f,
		...
                 &&xf0, &&xf1, &&xf2, &&xf3, &&xf4, &&xf5, &&xf6, &&xf7,
                 &&xf8, &&xf9, &&xfa, &&xfb, &&xfc, &&xfd, &&xfe, &&xff,
         };
#       define SWITCH(x)        goto *caselab[x];
#       define CASE(y)          cat(x,y)
#       define NEXT             if (INTR) goto ret; goto *caselab[nexti()]
#       define ENDSWITCH
#else
#       define SWITCH(x)        switch(x) {
#       define CASE(y)          case cat(0x,y)
#       define NEXT             if (INTR) goto ret; continue
#       define ENDSWITCH        }
#endif
	...
void
simulate(register CPU *cpu, register Byte *mem) {
	 for (;;) {
                 SWITCH(nextinst())
                 CASE(01): DO(NOP, 2);
                 CASE(02): DO(IDIV, 41);
                 CASE(03): DO(FDIV, 41);
		...
                 CASE(12): DO1(BRSET, DIR, 6);
		...
                 ENDSWITCH
         }
ret:
         RESTORE;
}