ZealOS/docs/Doc/Hash.DD.html
2021-12-11 06:10:58 -05:00

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<a name="l1"></a><span class=cFA>/* Graphics Not Rendered in HTML */</span><span class=cF0>
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<a name="l28"></a>There is a symbol (hash) table for each task. When a symbol is not found, the parent task's symbol table is checked. All
<a name="l29"></a>tasks chain back to the </span><span class=cF2>System</span><span class=cF0> task.
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<a name="l31"></a>ZealOS symbol tables are implemented with an array of linked-lists. A num is generated from a string by </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KHashA.ZC.html#l258"><span class=cF4>HashStr</span></a><span class=cF0>() to index
<a name="l32"></a>into the array of linked-lists. Multiple strings can generate the same num, so linked-lists are built. Newer entries
<a name="l33"></a>overshadow older ones.
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<a name="l35"></a>There are various types of entries. See </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KernelA.HH.html#l822"><span class=cF4>Hash Entry Types</span></a><span class=cF0>.
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<a name="l37"></a></span><span class=cF5>Symbol Look-up</span><span class=cF0> (Used many places including the </span><a href="https://zeal-operating-system.github.io/ZealOS/Compiler/Lex.ZC.html#l596"><span class=cF4>JIT Compiler</span></a><span class=cF0> and </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KLoad.ZC.html#l24"><span class=cF4>Loader</span></a><span class=cF0>.)
<a name="l38"></a>1) Symbol name is </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KHashA.ZC.html#l4"><span class=cF4>hashed</span></a><span class=cF0> by adding and shifting the ASCII of all chars.
<a name="l39"></a>2) </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KernelA.HH.html#l783"><span class=cF4>hash table</span></a><span class=cF0>-&gt;body[] array is indexed.
<a name="l40"></a>3) Linked-list is traversed until match of text and type of entry.
<a name="l41"></a>4) If not found, </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KernelA.HH.html#l783"><span class=cF4>hash table</span></a><span class=cF0>-&gt;next table is searched.
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<a name="l43"></a>Duplicate entries are allowed -- they overshadow old entries.
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<a name="l45"></a></span><span class=cF5>Address-to-Symbol Look-up</span><span class=cF0> (Slow because not important. We could use trees.)
<a name="l46"></a>1) FunSeg Cache is </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/FunSeg.ZC.html#l137"><span class=cF4>scanned</span></a><span class=cF0>.
<a name="l47"></a>2) Hash Tables are </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/FunSeg.ZC.html#l64"><span class=cF4>scanned</span></a><span class=cF0>.
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