OP_LESSTHANOREQUAL

INFO

Opcode number: 161
Byte representation: 0xa1
Short description: Pop the top two items; push 1 if the second is less than or equal to the top, 0 otherwise.

OP_LESSTHANOREQUAL compares the top two items on the stack as integers. If the second item is less than or equal to the top item, it pushes 1 (true) onto the stack. If not, it pushes an empty array (false). Both items are removed from the stack after the comparison.

Operation

1. Take the top item (a) and the second item (b) from the stack.
2. Compare the two items:
   • If b <= a, push 1 (true) onto the stack.
   • Otherwise, push an empty array (false) onto the stack.
3. Remove the original items (a and b) from the stack.

Notes

• Both items must be valid integers. Bitcoin Script interprets byte arrays up to 4 bytes as integers.
• An empty array ([]) is treated as 0 when compared.
• If there are fewer than two items on the stack when OP_GREATERTHAN is executed, the script will fail.

Examples

Example 1: Second item is less than the top item

# ASM script
OP_2 OP_3 OP_LESSTHANOREQUAL

# Raw script
5253a2

# Stack (before OP_LESSTHANOREQUAL)
3  # top
2

# Stack (after OP_LESSTHANOREQUAL)
1  # true, as 2 <= 3

Example 2: Second item is equal to the top item

# ASM script
OP_2 OP_2 OP_LESSTHANOREQUAL

# Raw script
5252a2

# Stack (before OP_LESSTHANOREQUAL)
2  # top
2

# Stack (after OP_LESSTHANOREQUAL)
1  # true, as 2 <= 2