Add OP_NUMNOTEQUAL page

Author: thunderbiscuit

.vitepress/config.js

@@ -171,7 +171,7 @@ export default {
         { text: "<code>155 | OP_BOOLOR</code>", link: "/opcodes/OP_BOOLOR.md" },
         { text: "<code>156 | OP_NUMEQUAL</code>", link: "/opcodes/OP_NUMEQUAL.md" },
         { text: "<code>157 | OP_NUMEQUALVERIFY</code>", link: "/opcodes/OP_NUMEQUALVERIFY.md" },
-        { text: "<code>158 | 🚧 OP_NUMNOTEQUAL</code>", link: "/opcodes/OP_NUMNOTEQUAL.md" },
+        { text: "<code>158 | OP_NUMNOTEQUAL</code>", link: "/opcodes/OP_NUMNOTEQUAL.md" },
         { text: "<code>159 | 🚧 OP_LESSTHAN</code>", link: "/opcodes/OP_LESSTHAN.md" },
         { text: "<code>160 | 🚧 OP_GREATERTHAN</code>", link: "/opcodes/OP_GREATERTHAN.md" },
         { text: "<code>161 | 🚧 OP_LESSTHANOREQUAL</code>", link: "/opcodes/OP_LESSTHANOREQUAL.md" },

opcodes/OP_NUMNOTEQUAL.md

@@ -1,5 +1,76 @@
-# Work In Progress
+# OP_NUMNOTEQUAL
 
-:::warning
-This page has not yet been written. If you have experience with bitcoin Script and would like to contribute, please do! You can open a PR [on the repository for this website](https://github.com/thunderbiscuit/opcode-explained).
+:::info
+**Opcode number:** 158  
+**Byte representation:** `0x9e`  
+**Short description:** Pop the top two stack items and push 0 if both are numerically equal, else push 1.
 :::
+
+`OP_NUMNOTEQUAL` compares the top two items on the stack as integers. If they are not numerically equal, it pushes `1` (`true`) onto the stack. If they are equal, it pushes an empty array (`false`). Both items are removed from the stack after the comparison.
+
+### Operation
+
+1. Remove the top two items from the stack.
+2. Compare them as integers:
+   - If they are **not equal**, push `1` (`true`) onto the stack.
+   - If they are equal, push an empty array (`false`) onto the stack.
+3. Both original items are removed.
+
+### Notes
+
+- Both items must be valid integers. Bitcoin Script interprets byte arrays up to **4 bytes** as signed integers.
+- An empty array (`[]`) is treated as `0` when compared.
+- If there are fewer than two items on the stack when `OP_NUMNOTEQUAL` is executed, the script will fail.
+
+## Examples
+
+### Example 1: Two unequal integers
+
+```shell
+# ASM script
+OP_2 OP_3 OP_NUMNOTEQUAL
+
+# Raw script
+52539e
+
+# Stack (before OP_NUMNOTEQUAL)
+3  # top
+2
+
+# Stack (after OP_NUMNOTEQUAL)
+1  # true, as 2 != 3
+```
+
+### Example 2: Two equal integers
+
+```shell
+# ASM script
+OP_2 OP_2 OP_NUMNOTEQUAL
+
+# Raw script
+52529e
+
+# Stack (before OP_NUMNOTEQUAL)
+2  # top
+2
+
+# Stack (after OP_NUMNOTEQUAL)
+[]  # false, as 2 == 2
+```
+
+### Example 3: Comparing zero with an empty array
+
+```shell
+# ASM script
+OP_0 OP_PUSHBYTES_1 00 OP_NUMNOTEQUAL
+
+# Raw script
+0001009e
+
+# Stack (before OP_NUMNOTEQUAL)
+00  # top (single zero byte)
+[]  # empty array
+
+# Stack (after OP_NUMNOTEQUAL)
+[]  # false, as 0 == [0x00]
+```