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case strings

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  case strings Roedy Green <see_website@mindprod.com.invalid> - 2012-06-03 11:40 -0700
    Re: case strings Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-03 13:37 -0700
      Re: case strings markspace <-@.> - 2012-06-03 19:19 -0700
      Re: case strings Roedy Green <see_website@mindprod.com.invalid> - 2012-06-04 07:53 -0700
        Re: case strings Lew <noone@lewscanon.com> - 2012-06-05 23:53 -0700
    Re: case strings Roedy Green <see_website@mindprod.com.invalid> - 2012-06-04 07:57 -0700
      Re: case strings "Mike Schilling" <mscottschilling@hotmail.com> - 2012-06-04 08:18 -0700
      Re: case strings Joshua Cranmer <Pidgeot18@verizon.invalid> - 2012-06-04 11:30 -0400
        Re: case strings Lew <noone@lewscanon.com> - 2012-06-06 00:15 -0700

#15017 — case strings

has anyone benchmarked or decompiled to see how the new case string
labels are compiled.  Are they faster than setting up a HashMap to
classify the strings?  In theory they could be since the literal
values are known at compile time, where HashMap does not have that
advantage.

-- 
Roedy Green Canadian Mind Products
http://mindprod.com
Controlling complexity is the essence of computer programming.
~ Brian W. Kernighan 1942-01-01
.

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#15020

On 6/3/12 11:40 AM, Roedy Green wrote:
> has anyone benchmarked or decompiled to see how the new case string
> labels are compiled.  Are they faster than setting up a HashMap to
> classify the strings?  In theory they could be since the literal
> values are known at compile time, where HashMap does not have that
> advantage.
>
It took me a second to realize you meant switch/case with Strings. I 
thought you were talking about letter case and case sensitivity, and the 
rest became a non sequitur.

I haven't looked into the mechanisms specifically, but I would imaging 
there could be significant optimizations that could be done at compile 
time (java->bytecode or bytecode->native), depending on size of the 
switch statement.

On the other hand, a Map has other advantages (like being able to be 
dynamically defined).  Use what ever is clearest for your use-case, then 
if, and only if, it isn't fast enough (as indicated by profiling tools), 
optimize it.

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#15024

On 6/3/2012 1:37 PM, Daniel Pitts wrote:
> It took me a second to realize you meant switch/case with Strings. I
> thought you were talking about letter case and case sensitivity, and the
> rest became a non sequitur.
>
> I haven't looked into the mechanisms specifically, but I would imaging


Thanks for translating from Roedyese into English.  I was having no luck 
at all with it.

Iirc, the strings in a case statement are hashed.  I seem to recall the 
implementer posting about how it worked, and he used a perfect hash for 
the strings, so it should be faster (slightly) than a regular hash map.

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#15041

On Sun, 03 Jun 2012 13:37:13 -0700, Daniel Pitts
<newsgroup.nospam@virtualinfinity.net> wrote, quoted or indirectly
quoted someone who said :

>
>On the other hand, a Map has other advantages (like being able to be 
>dynamically defined).  Use what ever is clearest for your use-case, then 
>if, and only if, it isn't fast enough (as indicated by profiling tools), 
>optimize it.

The primary motive for such questions is curiosity. Secondarily I want
to know which to use by default when there is no pressing high level
need for either.

I got immense joy looking as some of the assembler code that Jet
generated, realising is many cases it was faster than I would ever
have the patience to create, taking pipelines into consideration.

If I were to learn string labels were handled it some clever way it
would give me great pleasure.

It would be sort of like everyone being issued a Ferrari powered
electrically.
-- 
Roedy Green Canadian Mind Products
http://mindprod.com
Controlling complexity is the essence of computer programming.
~ Brian W. Kernighan 1942-01-01
.

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#15083

Roedy Green wrote:
> If I were to learn string labels were handled it some clever way it
> would give me great pleasure.


Joseph D. Darcy's Oracle Weblog
<https://blogs.oracle.com/darcy/entry/project_coin_string_switch_anatomy>
"... com.sun.tools.javac.comp.Lower, the compiler phase which translates away 
syntactic sugar, lowering structures to trees implementing the formerly 
sugar-coated functionality. For example, Lower already had a method to 
translate enum switches into a switch on an integer value retrieved from an 
enum → int map. The initial strings in switch implementation uses a similar 
technique: a single string switch in source code is lowered into a series of 
two switches. The first switch is a new synthesized switch on the string's 
hash code, which gets mapped to a label's ordinal position on the list of case 
statements. The second switch is structurally identical to the original string 
switch from the source except that the string case labels are replaced by 
integer positions and the computed position from the synthesized switch is the 
expression being switched on."

and about the compliance tests:

"The new tests verify that the proper structural checks are enforced for 
string switches as well as verify that the proper execution paths are taken on 
different inputs for switches with a variety of control flow shapes, including 
multiple case labels, case labels with colliding hash codes, and nested switches."

N.b., this article links to
<http://blogs.sun.com/darcy/entry/how_to_cross_compile_for>
"... make sure to set the bootclasspath!"

Thanks for the chance to flex my google-fu.

> It would be sort of like everyone being issued a Ferrari powered
> electrically.

That would be a Tesla.

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg

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#15042

On Sun, 03 Jun 2012 11:40:03 -0700, Roedy Green
<see_website@mindprod.com.invalid> wrote, quoted or indirectly quoted
someone who said :

>has anyone benchmarked or decompiled to see how the new case string
>labels are compiled.

I gather this was the confusing sentence.  What should I have called
the feature?

What the desperation of trying to deduce how it worked from benchmark
timings what threw you off?
-- 
Roedy Green Canadian Mind Products
http://mindprod.com
Controlling complexity is the essence of computer programming.
~ Brian W. Kernighan 1942-01-01
.

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#15045

"Roedy Green" <see_website@mindprod.com.invalid> wrote in message 
news:o2jps7t44ui9adpocgptdsrun43qgaalus@4ax.com...
> On Sun, 03 Jun 2012 11:40:03 -0700, Roedy Green
> <see_website@mindprod.com.invalid> wrote, quoted or indirectly quoted
> someone who said :
>
>>has anyone benchmarked or decompiled to see how the new case string
>>labels are compiled.
>
> I gather this was the confusing sentence.  What should I have called
> the feature?

Say, string-valued case labels. 

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#15046

On 6/4/2012 10:57 AM, Roedy Green wrote:
> On Sun, 03 Jun 2012 11:40:03 -0700, Roedy Green
> <see_website@mindprod.com.invalid>  wrote, quoted or indirectly quoted
> someone who said :
>
>> has anyone benchmarked or decompiled to see how the new case string
>> labels are compiled.
>
> I gather this was the confusing sentence.  What should I have called
> the feature?

Using switch with Strings?


-- 
Beware of bugs in the above code; I have only proved it correct, not 
tried it. -- Donald E. Knuth

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#15085

Joshua Cranmer wrote:
> Roedy Green wrote:
>>> has anyone benchmarked or decompiled to see how the new case string
>>> labels are compiled.
>>
>> I gather this was the confusing sentence. What should I have called
>> the feature?
>
> Using switch with Strings?

Strings in switch is the Project Coin name.

Also, string case labels.

The JLS calls them "switch labels", "case constants" and "case 
labels".(§14.11) (Case constants actually are only the constants within the 
case label, but that still pertains to Roedy's question.)

So do the programmers who implemented these constructs for Java.

But I had no trouble understanding that Roedy meant "string case labels" for 
"case string labels". The mere word transposition seemed like a typo.

-- 
Lew
Honi soit qui mal y pense.
http://upload.wikimedia.org/wikipedia/commons/c/cf/Friz.jpg

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