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3088 :: Rewrite of string case statements in hash map jump table

• cdome (orginal) [2017-08-02T11:22:16+02:00] view original

  Hi,

  I recall Araq mentioned Nim compiler rewrites string case statements into hash jump table for efficiency. Does anyone knows where is the code in compiler's codebase that does that.

  Thank you

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• Parashurama (orginal) [2017-08-02T11:33:17+02:00] view original

  you can find the code in

  $NIM_SRC_DIR/compiler/ccgexprs.nim
  Run

  inside proc genStringCase

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• cdome (orginal) [2017-08-02T11:43:29+02:00] view original

  Thanks Parashurama,

  Found genStringCase in ccgstmts.nim, but your hint was useful

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• Parashurama (orginal) [2017-08-02T11:47:53+02:00] view original

  I'm working on a similar problem. The performance for parsing/stringifying enums with holes is abysmal (in C anyway, JS is mostly fine).

  The problem is getting acceptable performance without importing the tables module which is kinda huge, needs modules math, hashes and others.

  I tried various implementation of parseEnum and I'm settling with a variant of binary search with a lookup table. (it's within ~10-20% of hashtable for Enums with ~8000 entries)

  Another factor is code length, basic linear search is very short but performan badly on Enums with ~100+ entries.

  PR is coming once I cleanup the code.

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