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Re: [PATCH]: Add new bytecode op `switch' for implementing branch tables

From: Clément Pit-Claudel
Subject: Re: [PATCH]: Add new bytecode op `switch' for implementing branch tables.
Date: Thu, 9 Feb 2017 14:15:35 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

On 2017-02-08 08:38, Vibhav Pant wrote:
> On Tue, Feb 7, 2017 at 9:26 PM, Clément Pit-Claudel
> <address@hidden> wrote:
>> The timings fluctuate quite a bit, but the byte-switch branch seems to be 
>> about 5-7% slower.  Hopefully linear-scan hash tables will make things much 
>> faster :)
> The following patch makes hash_lookup use linear search when the number of 
> keys
> in the hash table is <= 5 (chosen arbitrarily). switch bytecode run with this
> patch takes 15.96 seconds to run the benchmark, while the goto-if-nil code 
> takes
> 17.15 seconds.

Here's another test that your patch seems to improve a bit:

(defvar ~/maps nil)

(dotimes (n 50)
  (let ((map (make-hash-table :test #'eq)))
    (dotimes (k 2)
      (puthash k n map))
    (push map ~/maps)))

(benchmark-run-compiled 1000000
  (dolist (mp ~/maps)
    (gethash 1 mp)))

Are linear scans used on all small hash tables, then?


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