Often you can bound the running time --- certainly if there are no loops and you only use + - * and / operations. But, you are often screwed if there is a sin,

Often you can bound the running time --- certainly if there are no loops and you only use + - * and / operations. But, you are often screwed if there is a sin, cos, sqrt or other function that gives irrational results. You can sometimes get around sqrt function or other root functions by using an extension field, but I think I could count on one hand how many times I've done that.