Anthony Ferrara has a new post today getting into the details of how "equals" works in PHP at the opcode level. He focuses on the answer to a question he received:

I was asked an interesting question via email yesterday. The question is fairly simple. The answer, not so much... So, rather than reply in an email, I figured that I'd write a post about it instead. The question, simply stated, is: "When comparing a float to an integer using ==, where does the conversion happen?"

He starts with a super simple piece of test code that compares an integer (1) to a float (1.0) and walks through the process PHP takes to perform the comparison (with a double equals "=="). He talks about opcode handlers, the "fast equal function" and how it handles the casting from one type to another, C source highlights included.