Solidity – Gas Comparison Between <= and < Operators

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if(num <= 10) revert();

And

if(num < 11) revert();

Which of these statements consume less gas?

If we could save gas, we need not use less than/greater than equal to. We can just use less than or greater than along with the next integer.

Best Answer

LE (lower or equal) opcode does not exist on EVM, the operation is accomplished as a combination of existing opcodes. The specific combination will depend on the compiler version, optimizer, and code context, etc.

In that specific example the opcode for

    if(num <= 10) revert();

is

      PUSH A                push 10
      DUP2                  num
      GT                    num>10
      PUSH [tag] 15         tag if GT is true
      JUMPI                 jump if true

and for

    if(num < 11) revert();

is

      PUSH A                push 11
      DUP2                  num
      LT                    num<11
      ISZERO                negate LT
      PUSH [tag] 15         tag
      JUMPI                 jump if true

So, using < option will be 3 gas more expensive than using the <= due to the extra ISZERO opcode. But, in some cases like

     return num <= 10;

      PUSH A            10
      DUP3              num
      GT                num > 10
      ISZERO            negate GT

     return num < 11;

      PUSH B            11
      DUP3              num
      LT                num < 11

Using <= will be the one costing 3 more gas.

In conclusion, it depends on the code context which one is more efficient but, the 3-gas difference is negligible so, could consider using either.

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