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If we're going for doing it right of course the answer is
if(item.StartsWith("PF_", StringComparison.OrdinalIgnoreCase)) ...
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Well, if you will insist on writing code that other people can understand and maintain... 
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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I'm sorry I meant
if(1600548864 == (*(int*)&item.ToLower()) << 8) ...
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That's better! 
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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Nasty! Unsafe code...
Please, try to avoid it, especially when it can be done without it so much more clearly:
if (((BitConverter.ToInt32(Encoding.ASCII.GetBytes(item), 0) & 6250335) ^ 6243920) == 0)
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Clearly a functional language will magically make this far better:
((xum 567 487) (map item (lambda x (find (xor x (and y z)) (encode pi 49)))
The language is JavaScript. that of Mordor, which I will not utter here
I hold an A-7 computer expert classification, Commodore. I'm well acquainted with Dr. Daystrom's theories and discoveries. The basic design of all our ship's computers are JavaScript.
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CDP1802 wrote:
((xum 567 487) (map item (lambda x (find (xor x (and y z)) (encode pi 49)))
The language is JavaScript. that of Mordor, which I will not utter here
Man!  Javascript has changed!
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if(String.Equals(string1, string2, StringComparison.OrdinalIgnoreCase))
{
...
}
is faster than string.Compare
Please kill me now or erase any information about c# from my head.
Microsoft ... the only place where VARIANT_TRUE != true
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Are you sure? They both use a virtually identical approach behind the scenes.
And since the original code is only comparing the first three characters of the item string, you'd have to use Substring to create a new string before you could call Equals, which would almost certainly be slower.
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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Yes!
string string1 = File.ReadAllText(@"D:\Temp\MyText.txt");
string string2 = File.ReadAllText(@"D:\Temp\MyText.txt");
int x = 0;
Stopwatch sw1 = new Stopwatch();
sw1.Start();
for (int i = 0; i < 1000; i++)
{
if (String.Equals(string1, string2, StringComparison.OrdinalIgnoreCase))
{
x++;
}
}
sw1.Stop();
Console.WriteLine(x);
x = 0;
Stopwatch sw2 = new Stopwatch();
sw2.Start();
for (int i = 0; i < 1000; i++)
{
if (String.Compare(string1, string2, true) == 0)
{
x++;
}
}
sw2.Stop();
Console.WriteLine(x);
Console.WriteLine("{0}:{1}", sw1.ElapsedMilliseconds, sw2.ElapsedMilliseconds);
(The file is one of my standard test files: 1.6MB of Ipsum Lorem paragraphs)
Results:
1000
1000
1716:4071
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That's strange - on my computer, with a similar sized text file, Compare(string, string, bool) is consistently faster:
1000
1000
13997:3431
I'm running .NET 4.5.1 on Win7 x64.
Also, string.Compare(s1, s2, true) isn't the same as string.Equals(s1, s2, StringComparison.OrdinalIgnoreCase); it's equivalent to StringComparison.CurrentCultureIgnoreCase. Try using string.Compare(s1, s2, StringComparison.OrdinalIgnoreCase) instead.
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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Interesting: I'm also Win7/64, but .NET 4.0 rather than 4.5.
Adding OrdinalIgnoreCase:
string string1 = File.ReadAllText(@"D:\Temp\MyText.txt");
string string2 = File.ReadAllText(@"D:\Temp\MyText.txt");
int x = 0;
Stopwatch sw1 = new Stopwatch();
sw1.Start();
for (int i = 0; i < 1000; i++)
{
if (String.Equals(string1, string2, StringComparison.OrdinalIgnoreCase))
{
x++;
}
}
sw1.Stop();
Console.WriteLine(x);
x = 0;
Stopwatch sw2 = new Stopwatch();
sw2.Start();
for (int i = 0; i < 1000; i++)
{
if (String.Compare(string1, string2, true) == 0)
{
x++;
}
}
sw2.Stop();
Console.WriteLine(x);
x = 0;
Stopwatch sw3 = new Stopwatch();
sw3.Start();
for (int i = 0; i < 1000; i++)
{
if (String.Compare(string1, string2, StringComparison.OrdinalIgnoreCase) == 0)
{
x++;
}
}
sw3.Stop();
Console.WriteLine(x);
Console.WriteLine("{0}:{1}:{2}", sw1.ElapsedMilliseconds, sw2.ElapsedMilliseconds,sw3.ElapsedMilliseconds);
gives results similar to yours:
1000
1000
1000
1694:4087:1684 I'm surprised there is such a difference in performance between our machines: mine isn't anywhere near state of the art - more state of the ark!
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Ah, the mysteries of M$. Our life will be so empty and boring without them.
The same code (Sorry Griff i should pay you author rights)
the result was
1000
1000
1000
4359:2216:4383
.Net 4.5 Win 7/64
Microsoft ... the only place where VARIANT_TRUE != true
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Out of interest, are you building for "Any CPU", "x64" or "x32"?
Mine is built "x32" because that's what the app I shoved the code in is built for.
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The results i pasted was with "Any CPU"
x64
1000
1000
1000
5363:2199:5338
x86
1000
1000
1000
4530:2305:4519
Visual studio Premium 2012 version 11 with Update 3, Win7/64, .NET 4.5.50709 to be exact
Anyway i don't see how he gets ~14 seconds for String.Equals
P.S i should say i have problems with my hard at work. I am waiting for it to die. This also can affect the pasted data. I wonder what the results will be with reading from SSD
Note to myself : seconds comes after milliseconds not minutes. Stupid
Microsoft ... the only place where VARIANT_TRUE != true
modified 11-Dec-13 11:18am.
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It's milliseconds, so it was just under 14 seconds, not minutes! 
I'm running the code in LinqPad[^], and I've tried both with and without optimisations enabled, but it doesn't make a huge difference.
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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Yeah i know its in milliseconds but my upper processor forgot that after miliseconds seconds are next not minutes 
I am running it in debug mode with no optimisations.
Microsoft ... the only place where VARIANT_TRUE != true
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"I am running it in debug mode with no optimisations."
Why on earth try to benchmark code with no optimisations? Complete waste of time.
"If you don't fail at least 90 percent of the time, you're not aiming high enough."
Alan Kay.
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It must be .NET 4.5 - my machine's an early Vista-era dual-core.
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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You'll have to redo the test using the same textfile. I believe that's where most of the difference lies.
Politicians are always realistically manoeuvering for the next election. They are obsolete as fundamental problem-solvers.
Buckminster Fuller
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Could the difference be a extra file system filter driver slowing one down ?
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I've been always wondering why people just don't use string comparison functions with the case ignoring ability. Many languages have them. Why use ToLower or ToUpper if you don't really need that lowered string? One my colleague once told me that because of the belovers of ToUpper/ToLower the program he had to improve was doing its job during about 11 hours (the program was in C++)!!! After just replacing the appropriate functions with stricmp and similar ones (which compare ignoring the case) the program got the awesome performance boost: it managed to finish its execution in just one hour or such. Taste the difference!
lifecycle of a lifecycle of a lifecycle
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I would also have added a couple of .ToString()s somewhere, just to be sure 
Women are composed of carbon, hydrogen, oxygen and nitrogen; men are also composed of carbon, hydrogen, oxygen and nitrogen, but in such proportions that force respect.
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You really didn't think it through:
char p = item.charAt[0];
char f = item.charAt[1]
char u = item.charAt[1]
if (p == 'P' || p == 'p' &&
u == '_' &&
f == 'f' || p == 'F')
{
}
speramus in juniperus
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Nagy Vilmos wrote: f == 'f' || p == 'F'
Well that's just cruel! If you're going to rewrite it, at least make sure it works. 
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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