MaxDistance constant; some .cpp comments

libalee/corewords.cpp

@@ -154,11 +154,11 @@ execute:
 
         cell = state.pop();
         dcell = cell - state.dict.latest();
-        if (dcell > (1 << (sizeof(Cell) * 8 - 6)) - 1) {
+        if (dcell >= Dictionary::MaxDistance) {
             // Large distance to previous entry: store in dedicated cell.
             state.dict.write(static_cast<Addr>(cell) + sizeof(Cell),
                 static_cast<Cell>(dcell));
-            dcell = ((1 << (sizeof(Cell) * 8 - 6)) - 1);
+            dcell = Dictionary::MaxDistance;
         }
         state.dict.write(cell,
             (state.dict.read(cell) & 0x1F) | static_cast<Cell>(dcell << 6));

libalee/dictionary.cpp

@@ -37,7 +37,7 @@ Addr Dictionary::allot(Cell amount) noexcept
     if (neww < capacity()) {
         write(Here, static_cast<Addr>(neww));
     } else {
-        // TODO
+        // TODO how to handle allot failure? Error code?
     }
 
     return old;
@@ -64,7 +64,7 @@ void Dictionary::addDefinition(Word word) noexcept
     Cell wsize = word.size();
     add(wsize);
 
-    if (alignhere() - latest() >= ((1 << (sizeof(Cell) * 8 - 6)) - 1))
+    if (alignhere() - latest() >= MaxDistance)
         add(0);
 
     auto addr = allot(wsize);
@@ -86,7 +86,7 @@ Addr Dictionary::find(Word word) noexcept
         const Addr len = l & 0x1F;
         Word lw;
 
-        if ((l >> 6) < 1023) {
+        if ((l >> 6) < MaxDistance) {
             lw = Word::fromLength(lt + sizeof(Cell), len);
             if (equal(word, lw))
                 return lt;
@@ -114,7 +114,7 @@ Addr Dictionary::getexec(Addr addr) noexcept
     const Addr len = l & 0x1Fu;
 
     addr += sizeof(Cell);
-    if ((l >> 6) == 1023)
+    if ((l >> 6) == MaxDistance)
         addr += sizeof(Cell);
 
     addr += len;
@@ -125,7 +125,7 @@ bool Dictionary::hasInput() const noexcept
 {
     const Addr src = read(Dictionary::Source);
     const Addr end = read(Dictionary::SourceLen);
-    uint8_t idx = read(Dictionary::Input) & 0xFFu;
+    auto idx = static_cast<uint8_t>(read(Dictionary::Input));
 
     while (idx < end) {
         auto ch = readbyte(src + idx);
@@ -146,7 +146,7 @@ Word Dictionary::input() noexcept
 {
     const Addr src = read(Dictionary::Source);
     const Addr end = read(Dictionary::SourceLen);
-    uint8_t idx = read(Dictionary::Input) & 0xFFu;
+    auto idx = static_cast<uint8_t>(read(Dictionary::Input));
 
     Addr wstart = src + idx;
     Addr wend = wstart;

libalee/dictionary.hpp

@@ -41,7 +41,7 @@
  *    - bits 0..4: Length of name
  *    - bit 5: Set if word is immediate
  *    - bits 6..15: Distance (backwards) to the next entry
- *    - If bits 6..15 are all one-bits then distance is in the following cell.
+ *    - If bits 6..15 are all one-bits then "long" distance in following cell.
  *  - "Length" bytes of name
  *  - Zero or more bytes for address alignment
  *  - Zero or more bytes of the definition's contents
@@ -70,10 +70,10 @@ public:
     /** Stores the dictionary's "beginning" i.e. where new definitions begin. */
     constexpr static Addr Begin      = sizeof(Cell) * 8 + InputCells;
 
-    /**
-     * The "immediate" identifier bit used in a definition's information cell.
-     */
+    /** "Immediate" marker bit for a word's definition. */
     constexpr static Cell Immediate = (1 << 5);
+    /** Maximum "short" distance between two definitions. */
+    constexpr static Cell MaxDistance = (1 << (sizeof(Cell) * 8 - 6)) - 1;
 
     /** Returns the value of the cell at the given address. */
     virtual Cell read(Addr) const noexcept = 0;

libalee/parser.cpp

@@ -29,14 +29,17 @@ Error Parser::parse(State& state, const char *str)
 {
     auto addr = Dictionary::Input;
 
+    // Set source and input length
     const auto len = static_cast<Cell>(std::strlen(str));
     state.dict.write(addr, 0);
     state.dict.write(Dictionary::SourceLen, len);
 
+    // Fill input buffer with string contents
     addr += sizeof(Cell);
     while (*str)
         state.dict.writebyte(addr++, *str++);
 
+    // Zero the remaining input buffer
     while (addr < Dictionary::Input + Dictionary::InputCells)
         state.dict.writebyte(addr++, '\0');
 
@@ -56,8 +59,10 @@ Error Parser::parseSource(State& state)
 Error Parser::parseWord(State& state, Word word)
 {
     bool imm;
-    Addr ins = state.dict.find(word);
+    Addr ins;
 
+    // Search order: dictionary, core word-set, number, custom parse.
+    ins = state.dict.find(word);
     if (ins == 0) {
         auto cw = CoreWords::findi(state, word);
 
@@ -121,6 +126,9 @@ void Parser::processLiteral(State& state, Cell value)
     if (state.compiling()) {
         constexpr auto ins = CoreWords::token("_lit");
 
+        // Literal compression: opcodes between WordCount and Begin are unused,
+        // so we assign literals to them to save space. Opcode "WordCount"
+        // pushes zero to the stack, "WordCount + 1" pushes a one, etc.
         const Cell maxlit = Dictionary::Begin - CoreWords::WordCount;
         if (value >= 0 && value < maxlit)
             value += CoreWords::WordCount;

libalee/types.cpp

@@ -56,3 +56,4 @@ bool Word::iterator::operator!=(const iterator& other)
 {
     return dict != other.dict || addr != other.addr;
 }
+