replacing if-then-else strcmp ladders with switch cases
considering lib/dynamic_debug.c we have ... } else if (!strcmp(words[i], "module")) { rc = check_set(&query->module, words[i+1], "module"); } else if (!strcmp(words[i], "format")) { ... are there any built-in hash functions which would allow this ? switch (keyword) { case Hash("module"): ..... break; case Hash("format"): .... break; default: return -EINVAL }
On Fri, 12 Jun 2020 12:05:55 -0600, jim.cromie@gmail.com said:
considering lib/dynamic_debug.c we have
... } else if (!strcmp(words[i], "module")) { rc = check_set(&query->module, words[i+1], "module"); } else if (!strcmp(words[i], "format")) { ...
are there any built-in hash functions which would allow this ?
switch (keyword) { case Hash("module"): ..... break; case Hash("format"): .... break; default: return -EINVAL }
There's hash functions. But they're all cryptographic hashes that return things that are far too many bits to use as the index of a switch. Also, you have the problem that the cases of a switch have to be something that can be evaluated at compile time....
On Fri, Jun 12, 2020 at 11:02 PM Valdis Klētnieks <valdis.kletnieks@vt.edu> wrote:
On Fri, 12 Jun 2020 12:05:55 -0600, jim.cromie@gmail.com said:
considering lib/dynamic_debug.c we have
... } else if (!strcmp(words[i], "module")) { rc = check_set(&query->module, words[i+1], "module"); } else if (!strcmp(words[i], "format")) { ...
are there any built-in hash functions which would allow this ?
switch (keyword) { case Hash("module"): ..... break;
that should be: /* 2 compatible implementations */ #define chash(keywd) simple_hash_computed_by_compiler ( keywd ) #define rhash(keywd) simple_hash_computed_at_runtime ( keywd ) switch ( rhash (keyword) ) { case chash("module"): ... break;
There's hash functions. But they're all cryptographic hashes that return things that are far too many bits to use as the index of a switch.
Also, you have the problem that the cases of a switch have to be something that can be evaluated at compile time....
ok, so they dont exist. I suspect its doable, but needs big -fu, more than I got that said, I could imagine a compile-time check to insure that the simple-hash on a fixed dictionary yields no collision DEFINE_DICTIONARY( "dyndbg.control.adverbs", "module", "file", "line", "func" ) but thats not essential, since if theyre in case:s, the compiler would notice the collision, and so chash() doesnt need to do collision detection either. this would be slick, and I think usable more than once.
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jim.cromie＠gmail.com -
Valdis Klētnieks