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//! SHA-256
use crate::consts::{H224, H256, STATE_LEN};
use block_buffer::BlockBuffer;
use core::slice::from_ref;
use digest::consts::{U28, U32, U64};
use digest::generic_array::GenericArray;
use digest::{BlockInput, FixedOutputDirty, Reset, Update};

type BlockSize = U64;

/// Structure that keeps state of the Sha-256 operation and
/// contains the logic necessary to perform the final calculations.
#[derive(Clone)]
struct Engine256 {
    len: u64,
    buffer: BlockBuffer<BlockSize>,
    state: [u32; 8],
}

impl Engine256 {
    fn new(h: &[u32; STATE_LEN]) -> Engine256 {
        Engine256 {
            len: 0,
            buffer: Default::default(),
            state: *h,
        }
    }

    fn update(&mut self, input: &[u8]) {
        // Assumes that input.len() can be converted to u64 without overflow
        self.len += (input.len() as u64) << 3;
        let s = &mut self.state;
        self.buffer.input_blocks(input, |b| compress256(s, b));
    }

    fn finish(&mut self) {
        let s = &mut self.state;
        let l = self.len;
        self.buffer
            .len64_padding_be(l, |b| compress256(s, from_ref(b)));
    }

    fn reset(&mut self, h: &[u32; STATE_LEN]) {
        self.len = 0;
        self.buffer.reset();
        self.state = *h;
    }
}

/// The SHA-256 hash algorithm with the SHA-256 initial hash value.
#[derive(Clone)]
pub struct Sha256 {
    engine: Engine256,
}

impl Default for Sha256 {
    fn default() -> Self {
        Sha256 {
            engine: Engine256::new(&H256),
        }
    }
}

impl BlockInput for Sha256 {
    type BlockSize = BlockSize;
}

impl Update for Sha256 {
    fn update(&mut self, input: impl AsRef<[u8]>) {
        self.engine.update(input.as_ref());
    }
}

impl FixedOutputDirty for Sha256 {
    type OutputSize = U32;

    fn finalize_into_dirty(&mut self, out: &mut digest::Output<Self>) {
        self.engine.finish();
        let s = self.engine.state;
        for (chunk, v) in out.chunks_exact_mut(4).zip(s.iter()) {
            chunk.copy_from_slice(&v.to_be_bytes());
        }
    }
}

impl Reset for Sha256 {
    fn reset(&mut self) {
        self.engine.reset(&H256);
    }
}

/// The SHA-256 hash algorithm with the SHA-224 initial hash value. The result
/// is truncated to 224 bits.
#[derive(Clone)]
pub struct Sha224 {
    engine: Engine256,
}

impl Default for Sha224 {
    fn default() -> Self {
        Sha224 {
            engine: Engine256::new(&H224),
        }
    }
}

impl BlockInput for Sha224 {
    type BlockSize = BlockSize;
}

impl Update for Sha224 {
    fn update(&mut self, input: impl AsRef<[u8]>) {
        self.engine.update(input.as_ref());
    }
}

impl FixedOutputDirty for Sha224 {
    type OutputSize = U28;

    fn finalize_into_dirty(&mut self, out: &mut digest::Output<Self>) {
        self.engine.finish();
        let s = &self.engine.state[..7];
        for (chunk, v) in out.chunks_exact_mut(4).zip(s.iter()) {
            chunk.copy_from_slice(&v.to_be_bytes());
        }
    }
}

impl Reset for Sha224 {
    fn reset(&mut self) {
        self.engine.reset(&H224);
    }
}

opaque_debug::implement!(Sha224);
opaque_debug::implement!(Sha256);

digest::impl_write!(Sha224);
digest::impl_write!(Sha256);

cfg_if::cfg_if! {
    if #[cfg(feature = "force-soft")] {
        mod soft;
        use soft::compress;
    } else if #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {
        #[cfg(not(feature = "asm"))]
        mod soft;
        #[cfg(feature = "asm")]
        mod soft {
            pub(crate) fn compress(state: &mut [u32; 8], blocks: &[[u8; 64]]) {
                sha2_asm::compress256(state, blocks);
            }
        }
        mod x86;
        use x86::compress;
    } else if #[cfg(all(feature = "asm", target_arch = "aarch64", any(target_os = "macos", target_os = "linux")))] {
        mod soft;
        mod aarch64;
        use aarch64::compress;
    } else {
        mod soft;
        use soft::compress;
    }
}

/// Raw SHA-256 compression function.
///
/// This is a low-level "hazmat" API which provides direct access to the core
/// functionality of SHA-256.
#[cfg_attr(docsrs, doc(cfg(feature = "compress")))]
pub fn compress256(state: &mut [u32; 8], blocks: &[GenericArray<u8, U64>]) {
    // SAFETY: GenericArray<u8, U64> and [u8; 64] have
    // exactly the same memory layout
    #[allow(unsafe_code)]
    let blocks: &[[u8; 64]] = unsafe { &*(blocks as *const _ as *const [[u8; 64]]) };
    compress(state, blocks)
}