Opcode Explained

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OP_1SUB ​

INFO

Opcode number: 140
Byte representation: 0x8c
Short description: Decrement the top stack element in place.

OP_1SUB decrements the top item on the stack by 1. This opcode is used in bitcoin Script to perform basic arithmetic, such as reducing a counter or adjusting a value in more complex scripts.

Operation ​

  1. Take the top item from the stack.
  2. Subtract 1 from this item.
  3. Push the result back onto the stack as the new top item.

Notes ​

  • OP_1SUB only works with integer values (4 bytes). If the top item cannot be interpreted as an integer, the script will fail.
  • If the stack is empty when OP_1SUB is executed, the script will fail.

Example ​

Decrementing a stack item:

shell
# ASM script
OP_3 OP_1SUB

# Raw script
538c

# Stack (before OP_1SUB)
3

# Stack (after OP_1SUB)
2