emit loop in opcodes

Question

is there such thing as a 'while' loop opcode.
what are the opcodes i use to emit this loop:

int i = 0;
while(true)
{
if(i == 3)
{
break;
}

i++;
}

looking for something performance specific,

thanks in advance,

Jer,

J A · Answer

Hello all, I have attempted to write this using emit. Thanks in advance for any help. -Jer int i = 0; while(true) { i++; if(i >= 100) { break; } } I get: Unhandled Exception: System.InvalidProgramException: JIT Compiler encountered an internal limitation. at Hello() at test.Main(String[] d) test.cs //---------------------------------------- using System; using System.Reflection; using System.Reflection.Emit; public class test { private delegate int HelloDelegate(); public static void Main (string [] d) { DynamicMethod hello = new DynamicMethod("Hello", typeof(int), null, typeof(string).Module); Type[] writeStringArgs = {typeof(string)}; MethodInfo writeString = typeof(Console).GetMethod("WriteLine", writeStringArgs); ILGenerator il = hello.GetILGenerator(256); Label label1 = il.DefineLabel(); Label label2 = il.DefineLabel(); il.Emit(OpCodes.Ldc_I4_0); // 1 on stack il.MarkLabel(label2); il.Emit(OpCodes.Ldstr,"test"); // 2 on stack il.EmitCall(OpCodes.Call, writeString,null); // pop il.Emit(OpCodes.Ldc_I4_1); // 2 on stack il.Emit(OpCodes.Add); // 1 on stack il.Emit(OpCodes.Dup); // 2 on stack il.Emit(OpCodes.Ldc_I4,100); // 3 on stack il.Emit(OpCodes.Bge, label1); // if true, no stack il.Emit(OpCodes.Pop); // 1 popped il.Emit(OpCodes.Pop); // 1 popped il.Emit(OpCodes.Br_S,label2); // loop il.MarkLabel(label1); il.Emit(OpCodes.Ldc_I4_1); il.Emit(OpCodes.Ret); HelloDelegate hi = (HelloDelegate) hello.CreateDelegate(typeof(HelloDelegate)); hi(); } }

Alan · Answer

There isn't a specific opcode for a while loop. It's coded in much the same as it would be in assembler. If you put that code in a method and then examine the output with a disassembler such as ildasm or Redgate Reflector you'll see which opcodes are actually generated in the MSIL.

J A · Answer

opcode, is the code that the language is compiled down to, which is directly interpreted by the clr. using Reflection.Emit, dotnet api, you can code performance critical operations using opcodes from csharp. I am trying to learn how to use opcodes, and I would like to see how do take this standard csharp code, and code it using Emit opcodes. I have been scouring the net trying to find if there is a specific opcode for a 'while' expression. I hope this gives you enough info, so you can help. thanks in advance, Jer

Bechir Bejaoui · Answer

could you please more explain

emit loop in opcodes

Answers (4)