Opcode Explained

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OP_NUMEQUAL ​

INFO

Opcode number: 156
Byte representation: 0x9c
Short description: Pop the top two stack items and push 1 if both are numerically equal, else push 0.

OP_NUMEQUAL compares the top two items on the stack as integers. If they are numerically equal, it pushes 1 (true) onto the stack. If they are not equal, it pushes an empty array (false). Both items are removed from the stack after the comparison.

Operation ​

  1. Take the top two items from the stack.
  2. Compare them as integers:
    • If they are equal, push 1 (true) onto the stack.
    • If they are not 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 integers.
  • If there are fewer than two items on the stack when OP_NUMEQUAL is executed, the script will fail.

Examples ​

Example 1: Two equal integers ​

shell
# ASM script
OP_2 OP_2 OP_NUMEQUAL

# Raw script
52529c

# Stack (before OP_NUMEQUAL)
2  # top
2

# Stack (after OP_NUMEQUAL)
1

Example 2: Two unequal integers ​

shell
# ASM script
OP_2 OP_3 OP_NUMEQUAL

# Raw script
52539c

# Stack (before OP_NUMEQUAL)
3  # top
2

# Stack (after OP_NUMEQUAL)
[]

Example 3: Comparing zero with an empty array ​

shell
# ASM script
OP_PUSHBYTES_1 00 OP_0 OP_NUMEQUAL

# Raw script
0100009c

# Stack (before OP_NUMEQUAL)
[]  # top
0

# Stack (after OP_NUMEQUAL)
1  # true, as both are zero