compiler construction - What are best practices for arithmetic overflow checking in C#? -

there articles on web / stackoverflow usage of 'checked' keyword vs. compiler option 'check arithmetic overflow/underflow', those:

http://www.codethinked.com/c-trivia-what-no-overflow

why doesn't c# use arithmetic overflow checking default?

best way handle integer overflow in c#?

still don't know 1 should use. per default prefer go compiler option safe, not clutter code unchecked keyword, not forget in places , not commonly used, unknown many developers.

but how bad actual performance hit take? guess ms set default not overflow checking reason. compiler option concern code or every consumed libraries , framework itself?

i had same question. prefer piece of code checked default in company's code, because overflow side effects can cost lot , hard diagnose. discovering real reason of side effects can every valuable.

the question is, lose in terms of performance?

here simple bench :

static void main(string[] args) {     long c = 0;     var sw = new stopwatch();     sw.start();     unchecked     {         (long = 0; < 500000000; i++) c += 1;     }     sw.stop();     console.writeline("unchecked: " + sw.elapsedmilliseconds);      c = 0;     sw.restart();     checked     {         (long = 0; < 500000000; i++) c += 1;     }     sw.stop();     console.writeline("checked: " + sw.elapsedmilliseconds); } 

in generated il, see checked , unchecked keyword determines whether add.ovf or add instruction used. (both debug , release configs)

il_001c:  ldloc.2 il_001d:  ldc.i4.1 il_001e:  conv.i8 il_001f:  add   il_0066:  ldloc.2 il_0067:  ldc.i4.1 il_0068:  conv.i8 il_0069:  add.ovf 

results (x64 host)

debug

• unchecked: 2371
• checked: 2437

release

• unchecked: 2088
• checked: 2266

other results replacing long(s) int(s) (x64 host)

debug

• unchecked: 1665
• checked: 1568

release

• unchecked: 189
• checked: 566

the performance hit there, looks more important choose right variable type go checked or unchecked. anyway doesn't change opinion. i'll turn on "check arithmetic overflow/underflow" in our projects! (advanced build settings).

when in need of performance, i'll use unchecked block.