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    <p><code>Enter</code> creates a stack frame, and <code>leave</code> destroys a stack frame. With the <code>0,0</code> parameters on the <code>enter</code>, they're basically equivalent to:</p> <pre><code>; enter push ebp mov ebp, esp ; leave mov esp, ebp pop ebp </code></pre> <p>Although it's not used in the code you posted, <code>enter</code> does support doing a bit more than the simple push/mov combination shown above. The first parameter to <code>enter</code> specifies an amount of space to allocate for local variables. For example, <code>enter 5, 0</code> is roughly equivalent to:</p> <pre><code>push ebp mov ebp, esp sub esp, 5 </code></pre> <p><code>Enter</code> also supports languages like Pascal that can use nested functions/procedures:</p> <pre><code>procedure X; procedure Y; begin { ... } end begin { ... } end </code></pre> <p>In a case like this, <code>Y</code> has access not only to its own local variables, but also to all variables local to <code>X</code>. These can be nested to arbitrary depth, so you could have a <code>Z</code> inside of <code>Y</code> that had access to its own local variables, and the variables of <code>Y</code> and the variables of <code>X</code>. The second parameter to <code>enter</code> specifies the nesting depth, so <code>X</code> would use <code>enter Sx, 0</code>, <code>Y</code> would use <code>enter Sy, 1</code> and <code>Z</code> would use <code>enter Sz, 2</code> (where <code>Sx</code>, <code>Sy</code> and <code>Sz</code> signify the size of variables local to <code>X</code>, <code>Y</code> and <code>Z</code> respectively).</p> <p>This would create a chain of stack frames to give <code>Z</code> access to variables local to <code>Y</code> and <code>X</code>, and so on. This becomes fairly non-trivial if the functions are recursive, so an invocation of <code>Z</code> can't just walk up the stack to the two most recent stack frames--it needs to skip across stack frames from previous invocations of itself, and go directly back to stack frames for the lexical parent function/procedure, which is different from its caller in the case of recursion.</p> <p>This complexity is also why C and C++ prohibit nested functions. Given the presence of enter/leave, they're fairly easy to support on Intel processors, but can be considerably more difficult on many other processors that lack such direct support.</p> <p>This also at least helps explain one other...feature of <code>enter</code>--for the trivial case being used here (i.e., <code>enter 0, 0</code>) it's quite a bit slower than the equivalent using <code>push</code>/<code>mov</code>.</p>
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    1. POENTER and LEAVE in Assembly?
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    1. USJerry Coffin
    1. USJerry Coffin
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    1. COso are they macros..?
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    2. CO@BlackBear: No, they're instructions, but they're kind of "shorthand" instructions -- you can accomplish the same without them.
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    3. COok got it :) (char limit)
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