Re: Replacing $mon with Jan, Feb, Mar by regex or other means

[BrowserUk]

Put the 3-char abbrevs into a string and use substr to pick out the right one.

perl -e"for my $mon (0..11) { print substr('JanFebMarAprMayJunJulAugSe
+pOctNovDec', $mon*3, 3), $/; }"
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec

Switch the quotes under unix.

---

Examine what is said, not who speaks.

1) When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
2) The only way of discovering the limits of the possible is to venture a little way past them into the impossible
3) Any sufficiently advanced technology is indistinguishable from magic.
Arthur C. Clarke.

[RMGir]

I know you probably weren't serious.

But it turns out that your approach isn't as slow as I thought it would be. It's still slower than using an array, but not terribly.

Benchmark: running inlineArrayLookup, preBuiltArrayLookup, strftimeLoo
+kup, substrLookup, each for at least 2 CPU seconds...
inlineArrayLookup:  2 wallclock secs ( 2.12 usr + -0.01 sys =  2.11 CP
+U) @ 543540.28/s (n=1146870)
preBuiltArrayLookup:  1 wallclock secs ( 2.04 usr + -0.01 sys =  2.03 
+CPU) @ 588310.34/s (n=1194270)
strftimeLookup:  3 wallclock secs ( 1.76 usr +  0.37 sys =  2.13 CPU) 
+@ 216666.20/s (n=461499)
substrLookup:  2 wallclock secs ( 2.09 usr +  0.00 sys =  2.09 CPU) @ 
+465374.16/s (n=972632)
                        Rate strftimeLookup substrLookup inlineArrayLo
+okup preBuiltArrayLookup
strftimeLookup      216666/s             --         -53%              
+-60%                -63%
substrLookup        465374/s           115%           --              
+-14%                -21%
inlineArrayLookup   543540/s           151%          17%              
+  --                 -8%
preBuiltArrayLookup 588310/s           172%          26%              
+  8%                  --

Comparing the strftime version isn't totally fair, since it's not a simple "month->string" converter, but requires a localtime list. But as others have pointed out, it will do locales correctly.
Read more... (1345 Bytes)

--
Mike

Edit: Added strftime variant which I had overlooked.

Edit by tye, change PRE to CODE around long lines

[Abigail-II]

To make a better comparison, you should strftimeLookup do a getMonthNumber as well. Now it's the only case that isn't penalized by an extra subroutine call. Or you could eliminate the call from all cases, the lookup time won't be different depending on the number of the month. Just use a fixed month number (but don't hardcode it as a literal, or else the compiler might pre-calculate some calculations).

Abigail

[RMGir]

I did consider that, but since the strftime variant was already losing badly, it didn't seem critical.

You're right, though, wrapping the fetch of @fixedLocaltime in a sub (returning a ref to the array) call kills the performance of the strftime variant a bit more.

$ perl testMonth.pl 
Benchmark: running inlineArrayLookup, preBuiltArrayLookup, strftimeLoo
+kup, strftimeSubLookup, substrLookup, each for at least 2 CPU seconds
+...
inlineArrayLookup:  2 wallclock secs ( 2.12 usr +  0.00 sys =  2.12 CP
+U) @ 513847.17/s (n=1089356)
preBuiltArrayLookup:  2 wallclock secs ( 2.09 usr +  0.01 sys =  2.10 
+CPU) @ 568700.00/s (n=1194270)
strftimeLookup:  1 wallclock secs ( 1.81 usr +  0.35 sys =  2.16 CPU) 
+@ 223003.24/s (n=481687)
strftimeSubLookup:  2 wallclock secs ( 1.74 usr +  0.26 sys =  2.00 CP
+U) @ 182455.50/s (n=364911)
substrLookup:  2 wallclock secs ( 2.19 usr +  0.01 sys =  2.20 CPU) @ 
+446835.91/s (n=983039)
                        Rate strftimeSubLookup strftimeLookup substrLo
+okup inlineArrayLookup preBuiltArrayLookup
strftimeSubLookup   182455/s                --           -18%         
+-59%              -64%                -68%
strftimeLookup      223003/s               22%             --         
+-50%              -57%                -61%
substrLookup        446836/s              145%           100%         
+  --              -13%                -21%
inlineArrayLookup   513847/s              182%           130%         
+ 15%                --                -10%
preBuiltArrayLookup 568700/s              212%           155%         
+ 27%               11%                  --


--
Mike

Edit by tye, change PRE to CODE around long lines

[BrowserUk]

I do use this, though I usually put the constant information into a constant.

 use constant MONTHS=> 'JanFebMarAprMayJunJulAugSepOctNovDec';

You'll find that this has little if any effect on the performance.

---

Examine what is said, not who speaks.
1) When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
2) The only way of discovering the limits of the possible is to venture a little way past them into the impossible
3) Any sufficiently advanced technology is indistinguishable from magic.
Arthur C. Clarke.