OP_ABS

INFO

Opcode number: 144
Byte representation: 0x90
Short description: Converts the top item on the stack to its absolute value.

OP_ABS changes the top item on the stack to its absolute value, effectively removing any negative sign if present. This operation is useful when only the magnitude of a number is needed, regardless of its original sign.

Operation

1. Take the top item from the stack.
2. If the item is negative, make it positive.
3. Push the result back onto the stack as the new top item.

Notes

• OP_ABS works only on items that can be interpreted as integers, which in Bitcoin Script means byte arrays up to 4 bytes in length.
• If the top item is already positive or zero, applying OP_ABS has no effect.
• If the stack is empty when OP_ABS is executed, the script will fail.

Examples

Example 1

Converting a negative integer to its absolute value:

# ASM script
OP_1NEGATE OP_ABS

# Raw script
8f90

# Stack (before OP_ABS)
-1  # top

# Stack (after OP_ABS)
1  # result after taking absolute value

Example 2

Applying OP_ABS to a positive integer:

# ASM script
OP_2 OP_ABS

# Raw script
5290

# Stack (before OP_ABS)
2  # top

# Stack (after OP_ABS)
2  # no change, already positive