Well, you could try:
// ...
TF1 *f1 = new TF1("f1", myfunc, emin, emax, 0);
f1->SetNpx(10000);
// ...
TF1Convolution *f_conv = new TF1Convolution(f1, f1, emin, emax, false);
TF1 *f = new TF1("f", *f_conv, emin, emax, f_conv->GetNpar());
f->SetNpx(10000);
f->Draw();
gPad->SetLogx();
// ...
but be aware that, it internally calculates integrals of your “f1”. 
