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diff --git a/docs/Stacker.html b/docs/Stacker.html new file mode 100644 index 0000000000..bdd41bbfe5 --- /dev/null +++ b/docs/Stacker.html @@ -0,0 +1,1412 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" + "http://www.w3.org/TR/html4/strict.dtd"> +<html> +<head> + <title>Stacker: An Example Of Using LLVM</title> + <link rel="stylesheet" href="llvm.css" type="text/css"> +</head> +<body> + +<div class="doc_title">Stacker: An Example Of Using LLVM</div> + +<ol> + <li><a href="#abstract">Abstract</a></li> + <li><a href="#introduction">Introduction</a></li> + <li><a href="#lessons">Lessons I Learned About LLVM</a> + <ol> + <li><a href="#value">Everything's a Value!</a></li> + <li><a href="#terminate">Terminate Those Blocks!</a></li> + <li><a href="#blocks">Concrete Blocks</a></li> + <li><a href="#push_back">push_back Is Your Friend</a></li> + <li><a href="#gep">The Wily GetElementPtrInst</a></li> + <li><a href="#linkage">Getting Linkage Types Right</a></li> + <li><a href="#constants">Constants Are Easier Than That!</a></li> + </ol></li> + <li><a href="#lexicon">The Stacker Lexicon</a> + <ol> + <li><a href="#stack">The Stack</a></li> + <li><a href="#punctuation">Punctuation</a></li> + <li><a href="#comments">Comments</a></li> + <li><a href="#literals">Literals</a></li> + <li><a href="#words">Words</a></li> + <li><a href="#style">Standard Style</a></li> + <li><a href="#builtins">Built-Ins</a></li> + </ol></li> + <li><a href="#example">Prime: A Complete Example</a></li> + <li><a href="#internal">Internal Code Details</a> + <ol> + <li><a href="#directory">The Directory Structure </a></li> + <li><a href="#lexer">The Lexer</a></li> + <li><a href="#parser">The Parser</a></li> + <li><a href="#compiler">The Compiler</a></li> + <li><a href="#runtime">The Runtime</a></li> + <li><a href="#driver">Compiler Driver</a></li> + <li><a href="#tests">Test Programs</a></li> + <li><a href="#exercise">Exercise</a></li> + <li><a href="#todo">Things Remaining To Be Done</a></li> + </ol></li> +</ol> + +<div class="doc_author"> + <p>Written by <a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p> +</div> + +<!-- ======================================================================= --> +<div class="doc_section"><a name="abstract">Abstract</a></div> +<div class="doc_text"> +<p>This document is another way to learn about LLVM. Unlike the +<a href="LangRef.html">LLVM Reference Manual</a> or +<a href="ProgrammersManual.html">LLVM Programmer's Manual</a>, here we learn +about LLVM through the experience of creating a simple programming language +named Stacker. Stacker was invented specifically as a demonstration of +LLVM. The emphasis in this document is not on describing the +intricacies of LLVM itself but on how to use it to build your own +compiler system.</p> +</div> +<!-- ======================================================================= --> +<div class="doc_section"> <a name="introduction">Introduction</a> </div> +<div class="doc_text"> +<p>Amongst other things, LLVM is a platform for compiler writers. +Because of its exceptionally clean and small IR (intermediate +representation), compiler writing with LLVM is much easier than with +other system. As proof, I wrote the entire compiler (language definition, +lexer, parser, code generator, etc.) in about <em>four days</em>! +That's important to know because it shows how quickly you can get a new +language running when using LLVM. Furthermore, this was the <em >first</em> +language the author ever created using LLVM. The learning curve is +included in that four days.</p> +<p>The language described here, Stacker, is Forth-like. Programs +are simple collections of word definitions, and the only thing definitions +can do is manipulate a stack or generate I/O. Stacker is not a "real" +programming language; it's very simple. Although it is computationally +complete, you wouldn't use it for your next big project. However, +the fact that it is complete, it's simple, and it <em>doesn't</em> have +a C-like syntax make it useful for demonstration purposes. It shows +that LLVM could be applied to a wide variety of languages.</p> +<p>The basic notions behind stacker is very simple. There's a stack of +integers (or character pointers) that the program manipulates. Pretty +much the only thing the program can do is manipulate the stack and do +some limited I/O operations. The language provides you with several +built-in words that manipulate the stack in interesting ways. To get +your feet wet, here's how you write the traditional "Hello, World" +program in Stacker:</p> +<p><code>: hello_world "Hello, World!" >s DROP CR ;<br> +: MAIN hello_world ;<br></code></p> +<p>This has two "definitions" (Stacker manipulates words, not +functions and words have definitions): <code>MAIN</code> and <code> +hello_world</code>. The <code>MAIN</code> definition is standard; it +tells Stacker where to start. Here, <code>MAIN</code> is defined to +simply invoke the word <code>hello_world</code>. The +<code>hello_world</code> definition tells stacker to push the +<code>"Hello, World!"</code> string on to the stack, print it out +(<code>>s</code>), pop it off the stack (<code>DROP</code>), and +finally print a carriage return (<code>CR</code>). Although +<code>hello_world</code> uses the stack, its net effect is null. Well +written Stacker definitions have that characteristic. </p> +<p>Exercise for the reader: how could you make this a one line program?</p> +</div> +<!-- ======================================================================= --> +<div class="doc_section"><a name="lessons"></a>Lessons I Learned About LLVM</div> +<div class="doc_text"> +<p>Stacker was written for two purposes: </p> +<ol> + <li>to get the author over the learning curve, and</li> + <li>to provide a simple example of how to write a compiler using LLVM.</li> +</ol> +<p>During the development of Stacker, many lessons about LLVM were +learned. Those lessons are described in the following subsections.<p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="value"></a>Everything's a Value!</div> +<div class="doc_text"> +<p>Although I knew that LLVM uses a Single Static Assignment (SSA) format, +it wasn't obvious to me how prevalent this idea was in LLVM until I really +started using it. Reading the <a href="ProgrammersManual.html"> +Programmer's Manual</a> and <a href="LangRef.html">Language Reference</a>, +I noted that most of the important LLVM IR (Intermediate Representation) C++ +classes were derived from the Value class. The full power of that simple +design only became fully understood once I started constructing executable +expressions for Stacker.</p> + +<p>This really makes your programming go faster. Think about compiling code +for the following C/C++ expression: <code>(a|b)*((x+1)/(y+1))</code>. Assuming +the values are on the stack in the order a, b, x, y, this could be +expressed in stacker as: <code>1 + SWAP 1 + / ROT2 OR *</code>. +You could write a function using LLVM that computes this expression like +this: </p> + +<div class="doc_code"><pre> +Value* +expression(BasicBlock* bb, Value* a, Value* b, Value* x, Value* y ) +{ + ConstantSInt* one = ConstantSInt::get(Type::IntTy, 1); + BinaryOperator* or1 = BinaryOperator::createOr(a, b, "", bb); + BinaryOperator* add1 = BinaryOperator::createAdd(x, one, "", bb); + BinaryOperator* add2 = BinaryOperator::createAdd(y, one, "", bb); + BinaryOperator* div1 = BinaryOperator::createDiv(add1, add2, "", bb); + BinaryOperator* mult1 = BinaryOperator::createMul(or1, div1, "", bb); + return mult1; +} +</pre></div> + +<p>"Okay, big deal," you say? It is a big deal. Here's why. Note that I didn't +have to tell this function which kinds of Values are being passed in. They could be +<code>Instruction</code>s, <code>Constant</code>s, <code>GlobalVariable</code>s, or +any of the other subclasses of <code>Value</code> that LLVM supports. +Furthermore, if you specify Values that are incorrect for this sequence of +operations, LLVM will either notice right away (at compilation time) or the LLVM +Verifier will pick up the inconsistency when the compiler runs. In either case +LLVM prevents you from making a type error that gets passed through to the +generated program. This <em>really</em> helps you write a compiler that +always generates correct code!<p> +<p>The second point is that we don't have to worry about branching, registers, +stack variables, saving partial results, etc. The instructions we create +<em>are</em> the values we use. Note that all that was created in the above +code is a Constant value and five operators. Each of the instructions <em>is</em> +the resulting value of that instruction. This saves a lot of time.</p> +<p>The lesson is this: <em>SSA form is very powerful: there is no difference +between a value and the instruction that created it.</em> This is fully +enforced by the LLVM IR. Use it to your best advantage.</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="terminate"></a>Terminate Those Blocks!</div> +<div class="doc_text"> +<p>I had to learn about terminating blocks the hard way: using the debugger +to figure out what the LLVM verifier was trying to tell me and begging for +help on the LLVMdev mailing list. I hope you avoid this experience.</p> +<p>Emblazon this rule in your mind:</p> +<ul> + <li><em>All</em> <code>BasicBlock</code>s in your compiler <b>must</b> be + terminated with a terminating instruction (branch, return, etc.). + </li> +</ul> +<p>Terminating instructions are a semantic requirement of the LLVM IR. There +is no facility for implicitly chaining together blocks placed into a function +in the order they occur. Indeed, in the general case, blocks will not be +added to the function in the order of execution because of the recursive +way compilers are written.</p> +<p>Furthermore, if you don't terminate your blocks, your compiler code will +compile just fine. You won't find out about the problem until you're running +the compiler and the module you just created fails on the LLVM Verifier.</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="blocks"></a>Concrete Blocks</div> +<div class="doc_text"> +<p>After a little initial fumbling around, I quickly caught on to how blocks +should be constructed. In general, here's what I learned: +<ol> + <li><em>Create your blocks early.</em> While writing your compiler, you + will encounter several situations where you know apriori that you will + need several blocks. For example, if-then-else, switch, while, and for + statements in C/C++ all need multiple blocks for expression in LVVM. + The rule is, create them early.</li> + <li><em>Terminate your blocks early.</em> This just reduces the chances + that you forget to terminate your blocks which is required (go + <a href="#terminate">here</a> for more). + <li><em>Use getTerminator() for instruction insertion.</em> I noticed early on + that many of the constructors for the Instruction classes take an optional + <code>insert_before</code> argument. At first, I thought this was a mistake + because clearly the normal mode of inserting instructions would be one at + a time <em>after</em> some other instruction, not <em>before</em>. However, + if you hold on to your terminating instruction (or use the handy dandy + <code>getTerminator()</code> method on a <code>BasicBlock</code>), it can + always be used as the <code>insert_before</code> argument to your instruction + constructors. This causes the instruction to automatically be inserted in + the RightPlace™ place, just before the terminating instruction. The + nice thing about this design is that you can pass blocks around and insert + new instructions into them without ever knowing what instructions came + before. This makes for some very clean compiler design.</li> +</ol> +<p>The foregoing is such an important principal, its worth making an idiom:</p> +<pre> +BasicBlock* bb = new BasicBlock(); +bb->getInstList().push_back( new Branch( ... ) ); +new Instruction(..., bb->getTerminator() ); +</pre> +<p>To make this clear, consider the typical if-then-else statement +(see StackerCompiler::handle_if() method). We can set this up +in a single function using LLVM in the following way: </p> +<pre> +using namespace llvm; +BasicBlock* +MyCompiler::handle_if( BasicBlock* bb, SetCondInst* condition ) +{ + // Create the blocks to contain code in the structure of if/then/else + BasicBlock* then_bb = new BasicBlock(); + BasicBlock* else_bb = new BasicBlock(); + BasicBlock* exit_bb = new BasicBlock(); + + // Insert the branch instruction for the "if" + bb->getInstList().push_back( new BranchInst( then_bb, else_bb, condition ) ); + + // Set up the terminating instructions + then->getInstList().push_back( new BranchInst( exit_bb ) ); + else->getInstList().push_back( new BranchInst( exit_bb ) ); + + // Fill in the then part .. details excised for brevity + this->fill_in( then_bb ); + + // Fill in the else part .. details excised for brevity + this->fill_in( else_bb ); + + // Return a block to the caller that can be filled in with the code + // that follows the if/then/else construct. + return exit_bb; +} +</pre> +<p>Presumably in the foregoing, the calls to the "fill_in" method would add +the instructions for the "then" and "else" parts. They would use the third part +of the idiom almost exclusively (inserting new instructions before the +terminator). Furthermore, they could even recurse back to <code>handle_if</code> +should they encounter another if/then/else statement, and it will just work.</p> +<p>Note how cleanly this all works out. In particular, the push_back methods on +the <code>BasicBlock</code>'s instruction list. These are lists of type +<code>Instruction</code> (which is also of type <code>Value</code>). To create +the "if" branch we merely instantiate a <code>BranchInst</code> that takes as +arguments the blocks to branch to and the condition to branch on. The +<code>BasicBlock</code> objects act like branch labels! This new +<code>BranchInst</code> terminates the <code>BasicBlock</code> provided +as an argument. To give the caller a way to keep inserting after calling +<code>handle_if</code>, we create an <code>exit_bb</code> block which is +returned +to the caller. Note that the <code>exit_bb</code> block is used as the +terminator for both the <code>then_bb</code> and the <code>else_bb</code> +blocks. This guarantees that no matter what else <code>handle_if</code> +or <code>fill_in</code> does, they end up at the <code>exit_bb</code> block. +</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="push_back"></a>push_back Is Your Friend</div> +<div class="doc_text"> +<p> +One of the first things I noticed is the frequent use of the "push_back" +method on the various lists. This is so common that it is worth mentioning. +The "push_back" inserts a value into an STL list, vector, array, etc. at the +end. The method might have also been named "insert_tail" or "append". +Although I've used STL quite frequently, my use of push_back wasn't very +high in other programs. In LLVM, you'll use it all the time. +</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="gep"></a>The Wily GetElementPtrInst</div> +<div class="doc_text"> +<p> +It took a little getting used to and several rounds of postings to the LLVM +mailing list to wrap my head around this instruction correctly. Even though I had +read the Language Reference and Programmer's Manual a couple times each, I still +missed a few <em>very</em> key points: +</p> +<ul> +<li>GetElementPtrInst gives you back a Value for the last thing indexed.</li> +<li>All global variables in LLVM are <em>pointers</em>.</li> +<li>Pointers must also be dereferenced with the GetElementPtrInst +instruction.</li> +</ul> +<p>This means that when you look up an element in the global variable (assuming +it's a struct or array), you <em>must</em> deference the pointer first! For many +things, this leads to the idiom: +</p> +<pre> +std::vector<Value*> index_vector; +index_vector.push_back( ConstantSInt::get( Type::LongTy, 0 ); +// ... push other indices ... +GetElementPtrInst* gep = new GetElementPtrInst( ptr, index_vector ); +</pre> +<p>For example, suppose we have a global variable whose type is [24 x int]. The +variable itself represents a <em>pointer</em> to that array. To subscript the +array, we need two indices, not just one. The first index (0) dereferences the +pointer. The second index subscripts the array. If you're a "C" programmer, this +will run against your grain because you'll naturally think of the global array +variable and the address of its first element as the same. That tripped me up +for a while until I realized that they really do differ .. by <em>type</em>. +Remember that LLVM is strongly typed. Everything has a type. +The "type" of the global variable is [24 x int]*. That is, it's +a pointer to an array of 24 ints. When you dereference that global variable with +a single (0) index, you now have a "[24 x int]" type. Although +the pointer value of the dereferenced global and the address of the zero'th element +in the array will be the same, they differ in their type. The zero'th element has +type "int" while the pointer value has type "[24 x int]".</p> +<p>Get this one aspect of LLVM right in your head, and you'll save yourself +a lot of compiler writing headaches down the road.</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="linkage"></a>Getting Linkage Types Right</div> +<div class="doc_text"> +<p>Linkage types in LLVM can be a little confusing, especially if your compiler +writing mind has affixed firm concepts to particular words like "weak", +"external", "global", "linkonce", etc. LLVM does <em>not</em> use the precise +definitions of, say, ELF or GCC, even though they share common terms. To be fair, +the concepts are related and similar but not precisely the same. This can lead +you to think you know what a linkage type represents but in fact it is slightly +different. I recommend you read the +<a href="LangRef.html#linkage"> Language Reference on this topic</a> very +carefully. Then, read it again.<p> +<p>Here are some handy tips that I discovered along the way:</p> +<ul> + <li><em>Uninitialized means external.</em> That is, the symbol is declared in the current + module and can be used by that module, but it is not defined by that module.</li> + <li><em>Setting an initializer changes a global' linkage type.</em> Setting an + initializer changes a global's linkage type from whatever it was to a normal, + defined global (not external). You'll need to call the setLinkage() method to + reset it if you specify the initializer after the GlobalValue has been constructed. + This is important for LinkOnce and Weak linkage types.</li> + <li><em>Appending linkage can keep track of things.</em> Appending linkage can + be used to keep track of compilation information at runtime. It could be used, + for example, to build a full table of all the C++ virtual tables or hold the + C++ RTTI data, or whatever. Appending linkage can only be applied to arrays. + All arrays with the same name in each module are concatenated together at link + time.</li> +</ul> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="constants"></a>Constants Are Easier Than That!</div> +<div class="doc_text"> +<p> +Constants in LLVM took a little getting used to until I discovered a few utility +functions in the LLVM IR that make things easier. Here's what I learned: </p> +<ul> + <li>Constants are Values like anything else and can be operands of instructions</li> + <li>Integer constants, frequently needed, can be created using the static "get" + methods of the ConstantInt, ConstantSInt, and ConstantUInt classes. The nice thing + about these is that you can "get" any kind of integer quickly.</li> + <li>There's a special method on Constant class which allows you to get the null + constant for <em>any</em> type. This is really handy for initializing large + arrays or structures, etc.</li> +</ul> +</div> +<!-- ======================================================================= --> +<div class="doc_section"> <a name="lexicon">The Stacker Lexicon</a></div> +<div class="doc_text"><p>This section describes the Stacker language</p></div> +<div class="doc_subsection"><a name="stack"></a>The Stack</div> +<div class="doc_text"> +<p>Stacker definitions define what they do to the global stack. Before +proceeding, a few words about the stack are in order. The stack is simply +a global array of 32-bit integers or pointers. A global index keeps track +of the location of the top of the stack. All of this is hidden from the +programmer, but it needs to be noted because it is the foundation of the +conceptual programming model for Stacker. When you write a definition, +you are, essentially, saying how you want that definition to manipulate +the global stack.</p> +<p>Manipulating the stack can be quite hazardous. There is no distinction +given and no checking for the various types of values that can be placed +on the stack. Automatic coercion between types is performed. In many +cases, this is useful. For example, a boolean value placed on the stack +can be interpreted as an integer with good results. However, using a +word that interprets that boolean value as a pointer to a string to +print out will almost always yield a crash. Stacker simply leaves it +to the programmer to get it right without any interference or hindering +on interpretation of the stack values. You've been warned. :) </p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"> <a name="punctuation"></a>Punctuation</div> +<div class="doc_text"> +<p>Punctuation in Stacker is very simple. The colon and semi-colon +characters are used to introduce and terminate a definition +(respectively). Except for <em>FORWARD</em> declarations, definitions +are all you can specify in Stacker. Definitions are read left to right. +Immediately after the colon comes the name of the word being defined. +The remaining words in the definition specify what the word does. The definition +is terminated by a semi-colon.</p> +<p>So, your typical definition will have the form:</p> +<pre><code>: name ... ;</code></pre> +<p>The <code>name</code> is up to you but it must start with a letter and contain +only letters, numbers, and underscore. Names are case sensitive and must not be +the same as the name of a built-in word. The <code>...</code> is replaced by +the stack manipulating words that you wish to define <code>name</code> as. <p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="comments"></a>Comments</div> +<div class="doc_text"> + <p>Stacker supports two types of comments. A hash mark (#) starts a comment + that extends to the end of the line. It is identical to the kind of comments + commonly used in shell scripts. A pair of parentheses also surround a comment. + In both cases, the content of the comment is ignored by the Stacker compiler. The + following does nothing in Stacker. + </p> +<pre><code> +# This is a comment to end of line +( This is an enclosed comment ) +</code></pre> +<p>See the <a href="#example">example</a> program to see comments in use in +a real program.</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="literals"></a>Literals</div> +<div class="doc_text"> + <p>There are three kinds of literal values in Stacker: Integers, Strings, + and Booleans. In each case, the stack operation is to simply push the + value on to the stack. So, for example:<br/> + <code> 42 " is the answer." TRUE </code><br/> + will push three values on to the stack: the integer 42, the + string " is the answer.", and the boolean TRUE.</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="words"></a>Words</div> +<div class="doc_text"> +<p>Each definition in Stacker is composed of a set of words. Words are +read and executed in order from left to right. There is very little +checking in Stacker to make sure you're doing the right thing with +the stack. It is assumed that the programmer knows how the stack +transformation he applies will affect the program.</p> +<p>Words in a definition come in two flavors: built-in and programmer +defined. Simply mentioning the name of a previously defined or declared +programmer-defined word causes that word's stack actions to be invoked. It +is somewhat like a function call in other languages. The built-in +words have various effects, described <a href="#builtins">below</a>.</p> +<p>Sometimes you need to call a word before it is defined. For this, you can +use the <code>FORWARD</code> declaration. It looks like this:</p> +<p><code>FORWARD name ;</code></p> +<p>This simply states to Stacker that "name" is the name of a definition +that is defined elsewhere. Generally it means the definition can be found +"forward" in the file. But, it doesn't have to be in the current compilation +unit. Anything declared with <code>FORWARD</code> is an external symbol for +linking.</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="style"></a>Standard Style</div> +<div class="doc_text"> +<p>TODO</p> +</div> +<!-- ======================================================================= --> +<div class="doc_subsection"><a name="builtins"></a>Built In Words</div> +<div class="doc_text"> +<p>The built-in words of the Stacker language are put in several groups +depending on what they do. The groups are as follows:</p> +<ol> + <li><em>Logical</em>: These words provide the logical operations for + comparing stack operands.<br/>The words are: < > <= >= + = <> true false.</li> + <li><em>Bitwise</em>: These words perform bitwise computations on + their operands. <br/> The words are: << >> XOR AND NOT</li> + <li><em>Arithmetic</em>: These words perform arithmetic computations on + their operands. <br/> The words are: ABS NEG + - * / MOD */ ++ -- MIN MAX</li> + <li><em>Stack</em>These words manipulate the stack directly by moving + its elements around.<br/> The words are: DROP DROP2 NIP NIP2 DUP DUP2 + SWAP SWAP2 OVER OVER2 ROT ROT2 RROT RROT2 TUCK TUCK2 PICK SELECT ROLL</li> + <li><em>Memory</em>These words allocate, free, and manipulate memory + areas outside the stack.<br/>The words are: MALLOC FREE GET PUT</li> + <li><em>Control</em>: These words alter the normal left to right flow + of execution.<br/>The words are: IF ELSE ENDIF WHILE END RETURN EXIT RECURSE</li> + <li><em>I/O</em>: These words perform output on the standard output + and input on the standard input. No other I/O is possible in Stacker. + <br/>The words are: SPACE TAB CR >s >d >c <s <d <c.</li> +</ol> +<p>While you may be familiar with many of these operations from other +programming languages, a careful review of their semantics is important +for correct programming in Stacker. Of most importance is the effect +that each of these built-in words has on the global stack. The effect is +not always intuitive. To better describe the effects, we'll borrow from Forth the idiom of +describing the effect on the stack with:</p> +<p><code> BEFORE -- AFTER </code></p> +<p>That is, to the left of the -- is a representation of the stack before +the operation. To the right of the -- is a representation of the stack +after the operation. In the table below that describes the operation of +each of the built in words, we will denote the elements of the stack +using the following construction:</p> +<ol> + <li><em>b</em> - a boolean truth value</li> + <li><em>w</em> - a normal integer valued word.</li> + <li><em>s</em> - a pointer to a string value</li> + <li><em>p</em> - a pointer to a malloc'd memory block</li> +</ol> +</div> +<div class="doc_text" > + <table> +<tr><th colspan="4">Definition Of Operation Of Built In Words</th></tr> +<tr><th colspan="4"><b>LOGICAL OPERATIONS</b></th></tr> +<tr> + <td>Word</td> + <td>Name</td> + <td>Operation</td> + <td>Description</td> +</tr> +<tr> + <td><</td> + <td>LT</td> + <td>w1 w2 -- b</td> + <td>Two values (w1 and w2) are popped off the stack and + compared. If w1 is less than w2, TRUE is pushed back on + the stack, otherwise FALSE is pushed back on the stack.</td> +</tr> +<tr><td>></td> + <td>GT</td> + <td>w1 w2 -- b</td> + <td>Two values (w1 and w2) are popped off the stack and + compared. If w1 is greater than w2, TRUE is pushed back on + the stack, otherwise FALSE is pushed back on the stack.</td> +</tr> +<tr><td>>=</td> + <td>GE</td> + <td>w1 w2 -- b</td> + <td>Two values (w1 and w2) are popped off the stack and + compared. If w1 is greater than or equal to w2, TRUE is + pushed back on the stack, otherwise FALSE is pushed back + on the stack.</td> +</tr> +<tr><td><=</td> + <td>LE</td> + <td>w1 w2 -- b</td> + <td>Two values (w1 and w2) are popped off the stack and + compared. If w1 is less than or equal to w2, TRUE is + pushed back on the stack, otherwise FALSE is pushed back + on the stack.</td> +</tr> +<tr><td>=</td> + <td>EQ</td> + <td>w1 w2 -- b</td> + <td>Two values (w1 and w2) are popped off the stack and + compared. If w1 is equal to w2, TRUE is + pushed back on the stack, otherwise FALSE is pushed back + </td> +</tr> +<tr><td><></td> + <td>NE</td> + <td>w1 w2 -- b</td> + <td>Two values (w1 and w2) are popped off the stack and + compared. If w1 is equal to w2, TRUE is + pushed back on the stack, otherwise FALSE is pushed back + </td> +</tr> +<tr><td>FALSE</td> + <td>FALSE</td> + <td> -- b</td> + <td>The boolean value FALSE (0) is pushed on to the stack.</td> +</tr> +<tr><td>TRUE</td> + <td>TRUE</td> + <td> -- b</td> + <td>The boolean value TRUE (-1) is pushed on to the stack.</td> +</tr> +<tr><th colspan="4"><b>BITWISE OPERATORS</b></th></tr> +<tr> + <td>Word</td> + <td>Name</td> + <td>Operation</td> + <td>Description</td> +</tr> +<tr><td><<</td> + <td>SHL</td> + <td>w1 w2 -- w1<<w2</td> + <td>Two values (w1 and w2) are popped off the stack. The w2 + operand is shifted left by the number of bits given by the + w1 operand. The result is pushed back to the stack.</td> +</tr> +<tr><td>>></td> + <td>SHR</td> + <td>w1 w2 -- w1>>w2</td> + <td>Two values (w1 and w2) are popped off the stack. The w2 + operand is shifted right by the number of bits given by the + w1 operand. The result is pushed back to the stack.</td> +</tr> +<tr><td>OR</td> + <td>OR</td> + <td>w1 w2 -- w2|w1</td> + <td>Two values (w1 and w2) are popped off the stack. The values + are bitwise OR'd together and pushed back on the stack. This is + not a logical OR. The sequence 1 2 OR yields 3 not 1.</td> +</tr> +<tr><td>AND</td> + <td>AND</td> + <td>w1 w2 -- w2&w1</td> + <td>Two values (w1 and w2) are popped off the stack. The values + are bitwise AND'd together and pushed back on the stack. This is + not a logical AND. The sequence 1 2 AND yields 0 not 1.</td> +</tr> +<tr><td>XOR</td> + <td>XOR</td> + <td>w1 w2 -- w2^w1</td> + <td>Two values (w1 and w2) are popped off the stack. The values + are bitwise exclusive OR'd together and pushed back on the stack. + For example, The sequence 1 3 XOR yields 2.</td> +</tr> +<tr><th colspan="4"><b>ARITHMETIC OPERATORS</b></th></tr> +<tr> + <td>Word</td> + <td>Name</td> + <td>Operation</td> + <td>Description</td> +</tr> +<tr><td>ABS</td> + <td>ABS</td> + <td>w -- |w|</td> + <td>One value s popped off the stack; its absolute value is computed + and then pushed on to the stack. If w1 is -1 then w2 is 1. If w1 is + 1 then w2 is also 1.</td> +</tr> +<tr><td>NEG</td> + <td>NEG</td> + <td>w -- -w</td> + <td>One value is popped off the stack which is negated and then + pushed back on to the stack. If w1 is -1 then w2 is 1. If w1 is + 1 then w2 is -1.</td> +</tr> +<tr><td> + </td> + <td>ADD</td> + <td>w1 w2 -- w2+w1</td> + <td>Two values are popped off the stack. Their sum is pushed back + on to the stack</td> +</tr> +<tr><td> - </td> + <td>SUB</td> + <td>w1 w2 -- w2-w1</td> + <td>Two values are popped off the stack. Their difference is pushed back + on to the stack</td> +</tr> +<tr><td> * </td> + <td>MUL</td> + <td>w1 w2 -- w2*w1</td> + <td>Two values are popped off the stack. Their product is pushed back + on to the stack</td> +</tr> +<tr><td> / </td> + <td>DIV</td> + <td>w1 w2 -- w2/w1</td> + <td>Two values are popped off the stack. Their quotient is pushed back + on to the stack</td> +</tr> +<tr><td>MOD</td> + <td>MOD</td> + <td>w1 w2 -- w2%w1</td> + <td>Two values are popped off the stack. Their remainder after division + of w1 by w2 is pushed back on to the stack</td> +</tr> +<tr><td> */ </td> + <td>STAR_SLAH</td> + <td>w1 w2 w3 -- (w3*w2)/w1</td> + <td>Three values are popped off the stack. The product of w1 and w2 is + divided by w3. The result is pushed back on to the stack.</td> +</tr> +<tr><td> ++ </td> + <td>INCR</td> + <td>w -- w+1</td> + <td>One value is popped off the stack. It is incremented by one and then + pushed back on to the stack.</td> +</tr> +<tr><td> -- </td> + <td>DECR</td> + <td>w -- w-1</td> + <td>One value is popped off the stack. It is decremented by one and then + pushed back on to the stack.</td> +</tr> +<tr><td>MIN</td> + <td>MIN</td> + <td>w1 w2 -- (w2<w1?w2:w1)</td> + <td>Two values are popped off the stack. The larger one is pushed back + on to the stack.</td> +</tr> +<tr><td>MAX</td> + <td>MAX</td> + <td>w1 w2 -- (w2>w1?w2:w1)</td> + <td>Two values are popped off the stack. The larger value is pushed back + on to the stack.</td> +</tr> +<tr><th colspan="4"><b>STACK MANIPULATION OPERATORS</b></th></tr> +<tr> + <td>Word</td> + <td>Name</td> + <td>Operation</td> + <td>Description</td> +</tr> +<tr><td>DROP</td> + <td>DROP</td> + <td>w -- </td> + <td>One value is popped off the stack.</td> +</tr> +<tr><td>DROP2</td> + <td>DROP2</td> + <td>w1 w2 -- </td> + <td>Two values are popped off the stack.</td> +</tr> +<tr><td>NIP</td> + <td>NIP</td> + <td>w1 w2 -- w2</td> + <td>The second value on the stack is removed from the stack. That is, + a value is popped off the stack and retained. Then a second value is + popped and the retained value is pushed.</td> +</tr> +<tr><td>NIP2</td> + <td>NIP2</td> + <td>w1 w2 w3 w4 -- w3 w4</td> + <td>The third and fourth values on the stack are removed from it. That is, + two values are popped and retained. Then two more values are popped and + the two retained values are pushed back on.</td> +</tr> +<tr><td>DUP</td> + <td>DUP</td> + <td>w1 -- w1 w1</td> + <td>One value is popped off the stack. That value is then pushed on to + the stack twice to duplicate the top stack vaue.</td> +</tr> +<tr><td>DUP2</td> + <td>DUP2</td> + <td>w1 w2 -- w1 w2 w1 w2</td> |