// Copyright 2015-2025 Brian Smith.

//

// Permission to use, copy, modify, and/or distribute this software for any

// purpose with or without fee is hereby granted, provided that the above

// copyright notice and this permission notice appear in all copies.

//

// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES

// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF

// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY

// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES

// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION

// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN

// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

//! Building blocks.

use crate::{c, error};

use core::{ffi::c_int, num::NonZeroUsize};

mod boolmask;

mod leaky;

mod word;

pub(crate) use self::{boolmask::BoolMask, leaky::LeakyWord, word::Word};

/// Returns `Ok(())` if `a == b` and `Err(error::Unspecified)` otherwise.

pub fn verify_slices_are_equal(a: &[u8], b: &[u8]) -> Result<(), error::Unspecified> {

    let len = a.len(); // Arbitrary choice.

    if b.len() != len {

        return Err(error::Unspecified);

    }

    match NonZeroUsize::new(len) {

        Some(len) => {

            let a = a.as_ptr();

            let b = b.as_ptr();

            // SAFETY: `a` and `b` are valid non-null non-dangling pointers to `len`

            // bytes.

            let result = unsafe { CRYPTO_memcmp(a, b, len) };

            match result {

                0 => Ok(()),

                _ => Err(error::Unspecified),

            }

        }

        None => Ok(()), // Empty slices are equal.

    }

}

prefixed_extern! {

    fn CRYPTO_memcmp(a: *const u8, b: *const u8, len: c::NonZero_size_t) -> c_int;

}

pub(crate) fn xor_16(a: [u8; 16], b: [u8; 16]) -> [u8; 16] {

    let a = u128::from_ne_bytes(a);

    let b = u128::from_ne_bytes(b);

    let r = a ^ b;

    r.to_ne_bytes()

}

#[inline(always)]

pub(crate) fn xor_assign<'a>(a: impl IntoIterator<Item = &'a mut u8>, b: u8) {

    a.into_iter().for_each(|a| *a ^= b);

}

/// XORs the first N bytes of `b` into `a`, where N is

/// `core::cmp::min(a.len(), b.len())`.

#[inline(always)]

pub(crate) fn xor_assign_at_start<'a>(

    a: impl IntoIterator<Item = &'a mut u8>,

    b: impl IntoIterator<Item = &'a u8>,

) {

    a.into_iter().zip(b).for_each(|(a, b)| *a ^= *b);

}

#[cfg(test)]

mod tests {

    use super::*;

    use crate::{bssl, rand};

    fn leak_in_test(a: BoolMask) -> bool {

        a.leak()

    }

    #[test]

    fn test_constant_time() -> Result<(), error::Unspecified> {

        prefixed_extern! {

            fn bssl_constant_time_test_main() -> bssl::Result;

        }

        Result::from(unsafe { bssl_constant_time_test_main() })

    }

    #[test]

    fn constant_time_conditional_memcpy() -> Result<(), error::Unspecified> {

        let rng = rand::SystemRandom::new();

        for _ in 0..100 {

            let mut out = rand::generate::<[u8; 256]>(&rng)?.expose();

            let input = rand::generate::<[u8; 256]>(&rng)?.expose();

            // Mask to 16 bits to make zero more likely than it would otherwise be.

            let b = (rand::generate::<[u8; 1]>(&rng)?.expose()[0] & 0x0f) == 0;

            let ref_in = input;

            let ref_out = if b { input } else { out };

            prefixed_extern! {

                fn bssl_constant_time_test_conditional_memcpy(dst: &mut [u8; 256], src: &[u8; 256], b: BoolMask);

            }

            unsafe {

                bssl_constant_time_test_conditional_memcpy(

                    &mut out,

                    &input,

                    if b { BoolMask::TRUE } else { BoolMask::FALSE },

                )

            }

            assert_eq!(ref_in, input);

            assert_eq!(ref_out, out);

        }

        Ok(())

    }

    #[test]

    fn constant_time_conditional_memxor() -> Result<(), error::Unspecified> {

        let rng = rand::SystemRandom::new();

        for _ in 0..256 {

            let mut out = rand::generate::<[u8; 256]>(&rng)?.expose();

            let input = rand::generate::<[u8; 256]>(&rng)?.expose();

            // Mask to 16 bits to make zero more likely than it would otherwise be.

            let b = (rand::generate::<[u8; 1]>(&rng)?.expose()[0] & 0x0f) != 0;

            let ref_in = input;

            let mut ref_out = out;

            if b {

                xor_assign_at_start(&mut ref_out, &ref_in)

            };

            prefixed_extern! {

                fn bssl_constant_time_test_conditional_memxor(dst: &mut [u8; 256], src: &[u8; 256], b: BoolMask);

            }

            unsafe {

                bssl_constant_time_test_conditional_memxor(

                    &mut out,

                    &input,

                    if b { BoolMask::TRUE } else { BoolMask::FALSE },

                );

            }

            assert_eq!(ref_in, input);

            assert_eq!(ref_out, out);

        }

        Ok(())

    }

    #[test]

    fn test_bool_mask_bitwise_and_is_logical_and() {

        assert!(leak_in_test(BoolMask::TRUE & BoolMask::TRUE));

        assert!(!leak_in_test(BoolMask::TRUE & BoolMask::FALSE));

        assert!(!leak_in_test(BoolMask::FALSE & BoolMask::TRUE));

        assert!(!leak_in_test(BoolMask::FALSE & BoolMask::FALSE));

    }

}