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Comment by dividuum | Hacker News Reader

The alternative is to use the „labels as values“ feature of GCC. You can take the address of a label and later jump to it. I contributed the code that’s now in lc-addrlabels.h back in 2005 :-)

I also used the GCC local labels feature to completely avoid using __LINE__ anywhere, so you could have multiple coReturns in a single code line:

#define LC_SET(s) do { ({ __label__ resume; resume: (s) = &&resume; }); }while(0)

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Definitely, "labels as values" (aka "computed gotos", https://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html) is so much better than Duff's device.

Unfortunately, computed-gotos is not a C language standard. I don't understand why. I think FORTRAN had it in the 60s. It is so useful in some situations, like a coroutine, or a byte-code interpreter. Is it because some obscure DSP chip with a sizeof(char)==32 using 1's complement arithmetic can't support it? Then maybe make it implementation-defined and allow the rest of the world get nice things.

(For ease of reference—Fortran calls this an assigned GOTO: jump to label stored in a variable—as an integer number, as is Fortran’s way, not an address. A computed GOTO in Fortran is more like a switch statement in C: jump to the first label listed in the statement if the specified variable is one, to the second if it is two, ..., fall through to the next statement otherwise.)

Steve Wozniak's Integer BASIC (aka Apple BASIC) had computed-gotos too. Not sure about Microsoft BASIC, but Commodore BASIC had definitely lost this feature.

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