I'm not sure what you meant with the first solidity comment but for the second, yes this check wasn't correct, it was `n > 0`.

Meanwhile, the solidity commented code was missleading as well on the very last `if` statement, saying `// if n is even` while in fact the real condition was `if n is not even`.

I've been able to have consistent results after correcting the conditions

```cairo
    func fpow{syscall_ptr: felt*, pedersen_ptr: HashBuiltin*, range_check_ptr: felt}(
        x: Uint256,
        n: Uint256,
        baseUnit: Uint256
    ) -> (res: Uint256) {
        alloc_locals;

        let (xIsZero) = uint256_eq(x, Uint256(low=0, high=0));

        if(xIsZero == TRUE) {
            let (nIsZero) = uint256_eq(n, Uint256(low=0, high=0));
            if(nIsZero == TRUE) {
                // 0**0 = 1               
                return (res=Uint256(low=1, high=0));
            } 
            // 0**n = 0
            return (res=Uint256(low=0, high=0));
        }

        let (nHalf, nHalfRem) = uint256_unsigned_div_rem(n, Uint256(low=2, high=0));
        let (nIsEven) = uint256_eq(nHalfRem, Uint256(low=0, high=0));
        let (z) = FixedPointMathLib._assignZIf(nIsEven, baseUnit, x);

        let (baseUnitHalf, baseUnitHalfRem) = uint256_unsigned_div_rem(baseUnit, Uint256(low=2, high=0));

        let (res) = fpow_loop(x, nHalf, z, baseUnit, baseUnitHalf);

        return (res=res);
    }

    func fpow_loop{syscall_ptr: felt*, pedersen_ptr: HashBuiltin*, range_check_ptr: felt}(
        x: Uint256, 
        n: Uint256, 
        z: Uint256,
        baseUnit: Uint256,
        baseUnitHalf: Uint256
    ) -> (res: Uint256) {
        alloc_locals;

        let (n_LteZero) = uint256_le(n, Uint256(low=0, high=0));
        if(n_LteZero == TRUE) {
            return (res=z);
        }

        let (xx, xxOverflow) = uint256_mul(x, x);
        assert xxOverflow.low = 0;
        assert xxOverflow.high = 0;

        let (xxRound, xSquaredRoundCarry) = uint256_add(xx, baseUnitHalf);
        let (roundingOverflowed) = uint256_lt(xxRound, xx);
        assert roundingOverflowed = FALSE;

        let (temp_x, temp_x_rem) = uint256_unsigned_div_rem(xxRound, baseUnit);

        let (nHalf, nHalfRem) = uint256_unsigned_div_rem(n, Uint256(low=2, high=0));
        let (nHalfIsEven) = uint256_eq(nHalfRem, Uint256(low=0, high=0));
        if(nHalfIsEven == TRUE) {
            return fpow_loop(x=temp_x, n=nHalf, z=z, baseUnit=baseUnit, baseUnitHalf=baseUnitHalf);
        }

        let (zx, zxOverflow) = uint256_mul(z, temp_x);
        assert zxOverflow.low = 0;
        assert zxOverflow.high = 0;

        let (shouldBeZ, shouldBeZRem) = uint256_unsigned_div_rem(zx, temp_x);
        let (zxNotOverflowed) = uint256_eq(shouldBeZ, z);
        assert zxNotOverflowed = TRUE;

        let (zxRound, zxRoundCarry) = uint256_add(zx, baseUnitHalf);
        let (zxRoundOverflowed) = uint256_lt(zxRound, zx);
        assert zxRoundOverflowed = FALSE;

        let (temp_z, temp_zRem) = uint256_unsigned_div_rem(zxRound, baseUnit);

        return fpow_loop(x=temp_x, n=nHalf, z=temp_z, baseUnit=baseUnit, baseUnitHalf=baseUnitHalf);
    }
```

I'm trying to make a FixedPoint cairo lib, but I'm having some trouble making a pow function. 

It's inspired by this function

```solidity

    function pow(
        uint256 x,
        uint256 y,
        uint256 base
    ) internal pure returns (uint256 z) {
        assembly {
            switch x
            case 0 {
                switch y
                case 0 {
                    // 0 ** 0 = 1
                    z := base
                }
                default {
                    // 0 ** y = 0
                    z := 0
                }
            }
            default {
                switch mod(y, 2)
                case 0 {
                    // If y is even, store base in z for now.
                    z := base
                }
                default {
                    // If y is odd, store x in z for now.
                    z := x
                }

                // Shifting right by 1 is like dividing by 2.
                let half := shr(1, base)

                for {
                    // Shift y right by 1 before looping to halve it.
                    y := shr(1, y)
                } y {
                    // Shift y right by 1 each iteration to halve it.
                    y := shr(1, y)
                } {
                    // Revert immediately if x ** 2 would overflow.
                    // Equivalent to iszero(eq(div(xSquared, x), x)) here.
                    if shr(128, x) {
                        revert(0, 0)
                    }

                    // Store x squared.
                    let xSquared := mul(x, x)

                    // Round to the nearest number.
                    let xSquaredRound := add(xSquared, half)

                    // Revert if xSquared + half overflowed.
                    if lt(xSquaredRound, xSquared) {
                        revert(0, 0)
                    }

                    // Set x to scaled xSquaredRound.
                    x := div(xSquaredRound, base)

                    // If n is even:
                    if mod(y, 2) {
                        // Compute z * x.
                        let zx := mul(z, x)

                        // If z * x overflowed:
                        if iszero(eq(div(zx, x), z)) {
                            // Revert if x is non-zero.
                            if iszero(iszero(x)) {
                                revert(0, 0)
                            }
                        }

                        // Round to the nearest number.
                        let zxRound := add(zx, half)

                        // Revert if zx + half overflowed.
                        if lt(zxRound, zx) {
                            revert(0, 0)
                        }

                        // Return properly scaled zxRound.
                        z := div(zxRound, base)
                    }
                }
            }
        }
    }
```

and I wrote this one in Cairo

```cairo
    func pow{syscall_ptr: felt*, pedersen_ptr: HashBuiltin*, range_check_ptr: felt}(
        x: Uint256,
        n: Uint256,
        baseUnit: Uint256
    ) -> (res: Uint256) {
        alloc_locals;

        let (xIsZero) = uint256_eq(x, Uint256(low=0, high=0));

        if(xIsZero == TRUE) {
            let (nIsZero) = uint256_eq(n, Uint256(low=0, high=0));
            if(nIsZero == TRUE) {
                // 0**0 = 1
                return (res=Uint256(low=1, high=0));
            } 
            // 0**n = 0
            return (res=Uint256(low=0, high=0));            
        }

        let (nHalf, nHalfRem) = uint256_unsigned_div_rem(n, Uint256(low=2, high=0));
        let (nIsEven) = uint256_eq(nHalfRem, Uint256(low=0, high=0));
        let (z) = _assignZIf(nIsEven, baseUnit, x);

        let (baseUnitHalf, baseUnitHalfRem) = uint256_unsigned_div_rem(baseUnit, Uint256(low=2, high=0));

        let (res) = pow_loop(x, nHalf, z, baseUnit, baseUnitHalf);

        return (res=res);
    }

    func pow_loop{syscall_ptr: felt*, pedersen_ptr: HashBuiltin*, range_check_ptr: felt}(
        x: Uint256, 
        n: Uint256, 
        z: Uint256,
        baseUnit: Uint256,
        baseUnitHalf: Uint256
    ) -> (res: Uint256) {
        alloc_locals;
    
        let (n_LteOne) = uint256_le(n, Uint256(low=1, high=0));
        
        if(n_LteOne == TRUE) {
            return (res=z);
        }

        let (xx, xxOverflow) = uint256_mul(x, x);
        assert xxOverflow.low = 0;
        assert xxOverflow.high = 0;

        let (xxRound, xSquaredRoundCarry) = uint256_add(xx, baseUnitHalf);
        let (roundingOverflowed) = uint256_lt(xxRound, xx);
        assert roundingOverflowed = FALSE;

        let (temp_x, temp_x_rem) = uint256_unsigned_div_rem(xxRound, baseUnit);

        let (nHalf, nHalfRem) = uint256_unsigned_div_rem(n, Uint256(low=2, high=0));
        let (nHalfIsEven) = uint256_eq(nHalfRem, Uint256(low=0, high=0));
        if(nHalfIsEven ==  TRUE) {
            let (zx, zxOverflow) = uint256_mul(z, x);
            assert zxOverflow.low = 0;
            assert zxOverflow.high = 0;

            let (shouldBeZ, shouldBeZRem) = uint256_unsigned_div_rem(zx, x);
            let (zxNotOverflowed) = uint256_eq(shouldBeZ, z);
            assert zxNotOverflowed = TRUE;

            let (zxRound, zxRoundCarry) = uint256_add(zx, baseUnitHalf);
            let (zxRoundOverflowed) = uint256_lt(zxRound, zx);
            assert zxRoundOverflowed = FALSE;

            let (temp_z, temp_zRem) = uint256_unsigned_div_rem(zxRound, baseUnit);
            return pow_loop(x=temp_x, n=nHalf, z=temp_z, baseUnit=baseUnit, baseUnitHalf=baseUnitHalf);
        } else {
            return pow_loop(x=temp_x, n=nHalf, z=z, baseUnit=baseUnit, baseUnitHalf=baseUnitHalf);
        }
    }

    func _assignZIf{syscall_ptr: felt*, pedersen_ptr: HashBuiltin*, range_check_ptr: felt}(
        nIsEven: felt,
        baseUnit: Uint256,
        x: Uint256
    ) -> (res: Uint256) {
        if(nIsEven == TRUE) {
            return (res=baseUnit);
        }
        return (res=x);
    }
```

The thing is that I don't get the same results.

Here are some example of my results compared to the solidity function

- pow(1, 3, 10^18): Cairo = 1 / Solidity = 0

- pow(10^18, 5, 10^18): Cairo = 4000000000000000000 (4x10^18) / Solidity = 32000000000000000000 (32x10^18)

- pow(10^19, 5, 10^18): Cairo = 100000000000000000000 (10^20) / Solidity = 100000000000000000000000 (10^23)

I can't see what I'm doing wrong in my code

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