Posting code for general review is not appropriate here or on most Stack Exchange sites. It's too broad — Stack Exchange generally wants questions that can have a “definitive” answer.
There is however a Stack Exchange site which operates a little differently. You can post code for general review on Code Review. Do pay attention to their guidelines; in particular, the code must have no known bugs, i.e. you must post complete code that people can compile and it must be at least minimally tested.
If you're asking for very specific advice on some aspect of the code, such as performance or side channel resistance, then generally Stack Overflow is appropriate. Be sure to specify what you're concerned with, e.g. “my compiler doesn't put this variable in a register despite having free registers in this tight loop, how could I convince it?”.
Reviews for a very security-oriented aspect (e.g. side channel resistance) might get better feedback here than on SO. But here we generally frown on reading too much code, so focus on a small part (definitely don't post the full library in one go) an make sure your code is clear and well-commented.