69 lines
2.2 KiB
Markdown
69 lines
2.2 KiB
Markdown
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# Lua Programming Language
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## Lua 5.4 C API
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## Lua 5.4 Bytecode
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> [!note]
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> These are **unstable** and may differ in different versions of the language.
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> They are not part of the language specification but an implementation detail, which in this case is the reference implementation.
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> [!note]
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> The reference implementation used to have a stack based but now uses a register based VM similar to how modern real computer architectures.
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The instructions are 32 bits wide; every instruction has an opcode that takes up 7 bits, which leaves out 25 bits for the addresses and values.
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The instructions work with three register referred to as: A, B, C; each are of length 8 bits.
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<table>
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<thead>
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<tr>
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<th></th>
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<th>31</th><th>...</th><th>24</th><th>23</th><th>...</th><th>16</th><th>15</th><th>14</th><th>...</th><th>7</th><th>6</th><th>...</th><th>0</th>
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</tr>
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</thead>
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<tr>
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<td>iABC</td>
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<td colspan='3' style='text-align:center'>C (8 bits)</td>
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<td colspan='3' style='text-align:center'>B (8 bits)</td>
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<td style='text-align:center'>k (1 bit)</td>
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<td colspan='3' style='text-align:center'>A (8 bits)</td>
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<td colspan='3' style='text-align:center'>OP (7 bits)</td>
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</tr>
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<tr>
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<td>iABx</td>
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<td colspan='7' style='text-align:center'>B (17 bits)</td>
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<td colspan='3' style='text-align:center'>A (8 bits)</td>
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<td colspan='3' style='text-align:center'>OP (7 bits)</td>
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</tr>
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<tr>
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<td>iAsBx</td>
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<td colspan='7' style='text-align:center'>signed B 17 bits)</td>
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<td colspan='3' style='text-align:center'>A (8 bits)</td>
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<td colspan='3' style='text-align:center'>OP (7 bits)</td>
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</tr>
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<tr>
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<td>iAx</td>
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<td colspan='10' style='text-align:center'>Ax (25 bits)</td>
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<td colspan='3' style='text-align:center'>OP (7 bits)</td>
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</tr>
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<tr>
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<td>sJ</td>
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<td colspan='10' style='text-align:center'>signed jump address (25 bits)</td>
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<td colspan='3' style='text-align:center'>OP (7 bits)</td>
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</tr>
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</table>
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```lua
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-- arithmetic to calculate the lengths used from https://www.lua.org/source/5.4/lopcodes.h.html
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A = 8
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B = 8
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C = 8
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Bx = A + B + 1 -- 17
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Ax = A + Bx -- 25
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sJ = A + Bx -- 25
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```
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This page contains excerpts from Lua's source code which is the copyright of Lua.org, PUC-Rio and is licensed under the MIT License.
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[lua.org/license.html](https://www.lua.org/license.html)
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