OP_WITHIN

INFO

Opcode number: 165
Byte representation: 0xa5
Short description: Pop the top three items; if the first item is within the range specified by the second and third stack items, push 1, otherwise, push an empty array.

OP_WITHIN checks if the top item on the stack is within a specified range. Specifically, it evaluates whether the first item is greater than or equal to the second item and less than the third item (min <= x < max). If true, it pushes 1 (true) onto the stack; otherwise, it pushes an empty array (false).

Operation

1. Pop the top three items from the stack:
   • x (fist item): The value to check.
   • min (second item): The lower bound of the range.
   • max (third item): The upper bound of the range.
2. Evaluate whether min <= x < max:
   • If true, push 1 (true) onto the stack.
   • If false, push an empty array (false) onto the stack.

Notes

• The range is inclusive of the lower bound (min <= x) and exclusive of the upper bound (x < max).
• 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: Value is within the range

# ASM script
OP_2 OP_1 OP_3 OP_WITHIN

# Raw script
525153a5

# Stack (before OP_WITHIN)
3  # max
1  # min
2  # x

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

Example 3: Value is at the lower bound

# ASM script
OP_1 OP_1 OP_3 OP_WITHIN

# Raw script
515153a5

# Stack (before OP_WITHIN)
3  # top (max)
1  # min
1  # x

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