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sha2: add soft-compact backend (#686)
The new backend results in a much smaller binary code (e.g. for SHA-256 on `thumbv7em-none-eabi` we get [~150 instructions][0] vs [~1680 instructions][1], for SHA-512 it's [~330][2] vs [~7950][3]) while being somewhat slower on non-embedded CPUs (e.g. for SHA-256 on my x86-64 laptop with `opt-level=s` it results in 289 MB/s vs 315 MB/s). [0]: https://rust.godbolt.org/z/c5cT5chGz [1]: https://rust.godbolt.org/z/rWMTqaxdc [2]: https://rust.godbolt.org/z/EKoxxdqrv [3]: https://rust.godbolt.org/z/Td81PxsdW
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‎.github/workflows/sha2.yml‎

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@@ -79,6 +79,9 @@ jobs:
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- run: cargo test --all-features
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env:
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RUSTFLAGS: -Dwarnings --cfg sha2_backend="soft"
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- run: cargo test --all-features
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env:
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RUSTFLAGS: -Dwarnings --cfg sha2_backend="soft-compact"
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# macOS tests
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macos:
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- run: cargo test --all-features
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env:
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RUSTFLAGS: -Dwarnings --cfg sha2_backend="soft"
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- run: cargo test --all-features
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env:
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RUSTFLAGS: -Dwarnings --cfg sha2_backend="soft-compact"
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# Windows tests
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windows:
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- run: cargo test --all-features
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env:
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RUSTFLAGS: -Dwarnings --cfg sha2_backend="soft"
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- run: cargo test --all-features
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env:
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RUSTFLAGS: -Dwarnings --cfg sha2_backend="soft-compact"
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# Cross-compiled tests
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cross:
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- run: cross test --package sha2 --all-features --target riscv64gc-unknown-linux-gnu
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env:
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RUSTFLAGS: -Dwarnings --cfg sha2_backend="soft" -C target-feature=+zknh,+zbkb
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- run: cross test --package sha2 --all-features --target riscv64gc-unknown-linux-gnu
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env:
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RUSTFLAGS: -Dwarnings --cfg sha2_backend="soft-compact" -C target-feature=+zknh,+zbkb
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- run: cross test --package sha2 --all-features --target riscv64gc-unknown-linux-gnu
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env:
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RUSTFLAGS: -Dwarnings --cfg sha2_backend="riscv-zknh" -C target-feature=+zknh,+zbkb
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- run: cargo build --all-features --target riscv32gc-unknown-linux-gnu -Z build-std
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env:
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RUSTFLAGS: -Dwarnings --cfg sha2_backend="soft" -C target-feature=+zknh,+zbkb
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- run: cargo build --all-features --target riscv32gc-unknown-linux-gnu -Z build-std
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env:
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RUSTFLAGS: -Dwarnings --cfg sha2_backend="soft-compact" -C target-feature=+zknh,+zbkb
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- run: cargo build --all-features --target riscv32gc-unknown-linux-gnu -Z build-std
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env:
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RUSTFLAGS: -Dwarnings --cfg sha2_backend="riscv-zknh" -C target-feature=+zknh,+zbkb

‎sha2/CHANGELOG.md‎

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@@ -14,15 +14,25 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
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### Added
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- RISC-V scalar crypto extension support gated behind `sha2_backend = "riscv-zknh"` or
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`sha2_backend = "riscv-zknh-compact"` configuration flags ([#614])
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- `sha2_backend = "soft"` configuration flag ([#615])
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- `sha2_backend = "soft-compact"` configuration flag ([#686])
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### Removed
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- `asm`, `asm-aarch64`, `loongarch64_asm`, and `compress` crate features ([#542])
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- `soft` crate feature. Replaced with `sha2_backend = "soft"` configuration flag ([#615])
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- `soft` crate feature ([#615])
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- `force-soft-compact` crate feature ([#686])
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[#542]: https://github.com/RustCrypto/hashes/pull/542
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[#614]: https://github.com/RustCrypto/hashes/pull/614
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[#615]: https://github.com/RustCrypto/hashes/pull/615
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[#652]: https://github.com/RustCrypto/hashes/pull/652
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[#686]: https://github.com/RustCrypto/hashes/pull/686
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## 0.10.9 (2025-04-30)
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### Added
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- `force-soft-compact` crate feature to enable compact software backend (backport of [#686]) [#687]
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[#687]: https://github.com/RustCrypto/hashes/pull/687
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## 0.10.8 (2023-09-26)
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### Added

‎sha2/Cargo.toml‎

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@@ -36,7 +36,7 @@ oid = ["digest/oid"]
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[lints.rust.unexpected_cfgs]
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level = "warn"
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check-cfg = [
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'cfg(sha2_backend, values("soft", "riscv-zknh", "riscv-zknh-compact"))',
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'cfg(sha2_backend, values("soft", "soft-compact", "riscv-zknh", "riscv-zknh-compact"))',
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]
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[package.metadata.docs.rs]

‎sha2/src/sha256.rs‎

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@@ -2,6 +2,9 @@ cfg_if::cfg_if! {
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if #[cfg(sha2_backend = "soft")] {
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mod soft;
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use soft::compress;
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} else if #[cfg(sha2_backend = "soft-compact")] {
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mod soft_compact;
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use soft_compact::compress;
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} else if #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {
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mod soft;
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mod x86_shani;
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#[inline(always)]
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#[allow(dead_code)]
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fn to_u32s(block: &[u8; 64]) -> [u32; 16] {
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let mut res = [0u32; 16];
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for (src, dst) in block.chunks_exact(4).zip(res.iter_mut()) {
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*dst = u32::from_be_bytes(src.try_into().unwrap());
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}
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res
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core::array::from_fn(|i| {
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let chunk = block[4 * i..][..4].try_into().unwrap();
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u32::from_be_bytes(chunk)
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})
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}
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/// Raw SHA-256 compression function.

‎sha2/src/sha256/soft_compact.rs‎

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@@ -0,0 +1,56 @@
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use crate::consts::K32;
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fn compress_u32(state: &mut [u32; 8], block: [u32; 16]) {
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let [mut a, mut b, mut c, mut d, mut e, mut f, mut g, mut h] = *state;
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let mut w = [0; 64];
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w[..16].copy_from_slice(&block);
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for i in 16..64 {
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let w15 = w[i - 15];
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let s0 = (w15.rotate_right(7)) ^ (w15.rotate_right(18)) ^ (w15 >> 3);
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let w2 = w[i - 2];
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let s1 = (w2.rotate_right(17)) ^ (w2.rotate_right(19)) ^ (w2 >> 10);
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w[i] = w[i - 16]
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.wrapping_add(s0)
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.wrapping_add(w[i - 7])
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.wrapping_add(s1);
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}
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for i in 0..64 {
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let s1 = e.rotate_right(6) ^ e.rotate_right(11) ^ e.rotate_right(25);
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let ch = (e & f) ^ ((!e) & g);
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let t1 = s1
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.wrapping_add(ch)
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.wrapping_add(K32[i])
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.wrapping_add(w[i])
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.wrapping_add(h);
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let s0 = a.rotate_right(2) ^ a.rotate_right(13) ^ a.rotate_right(22);
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let maj = (a & b) ^ (a & c) ^ (b & c);
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let t2 = s0.wrapping_add(maj);
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h = g;
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g = f;
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f = e;
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e = d.wrapping_add(t1);
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d = c;
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c = b;
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b = a;
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a = t1.wrapping_add(t2);
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}
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state[0] = state[0].wrapping_add(a);
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state[1] = state[1].wrapping_add(b);
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state[2] = state[2].wrapping_add(c);
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state[3] = state[3].wrapping_add(d);
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state[4] = state[4].wrapping_add(e);
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state[5] = state[5].wrapping_add(f);
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state[6] = state[6].wrapping_add(g);
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state[7] = state[7].wrapping_add(h);
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}
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pub fn compress(state: &mut [u32; 8], blocks: &[[u8; 64]]) {
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for block in blocks.iter() {
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compress_u32(state, super::to_u32s(block));
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}
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}

‎sha2/src/sha512.rs‎

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@@ -2,6 +2,9 @@ cfg_if::cfg_if! {
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if #[cfg(sha2_backend = "soft")] {
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mod soft;
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use soft::compress;
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} else if #[cfg(sha2_backend = "soft-compact")] {
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mod soft_compact;
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use soft_compact::compress;
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} else if #[cfg(any(target_arch = "x86", target_arch = "x86_64"))] {
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mod soft;
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mod x86_avx2;
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#[inline(always)]
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#[allow(dead_code)]
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fn to_u64s(block: &[u8; 128]) -> [u64; 16] {
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let mut res = [0u64; 16];
43-
for (src, dst) in block.chunks_exact(8).zip(res.iter_mut()) {
44-
*dst = u64::from_be_bytes(src.try_into().unwrap());
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}
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res
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core::array::from_fn(|i| {
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let chunk = block[8 * i..][..8].try_into().unwrap();
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u64::from_be_bytes(chunk)
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})
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}
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/// Raw SHA-512 compression function.

‎sha2/src/sha512/soft_compact.rs‎

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use crate::consts::K64;
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fn compress_u64(state: &mut [u64; 8], block: [u64; 16]) {
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let [mut a, mut b, mut c, mut d, mut e, mut f, mut g, mut h] = *state;
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let mut w = [0; 80];
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w[..16].copy_from_slice(&block);
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for i in 16..80 {
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let w15 = w[i - 15];
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let s0 = (w15.rotate_right(1)) ^ (w15.rotate_right(8)) ^ (w15 >> 7);
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let w2 = w[i - 2];
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let s1 = (w2.rotate_right(19)) ^ (w2.rotate_right(61)) ^ (w2 >> 6);
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w[i] = w[i - 16]
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.wrapping_add(s0)
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.wrapping_add(w[i - 7])
17+
.wrapping_add(s1);
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}
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for i in 0..80 {
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let s1 = e.rotate_right(14) ^ e.rotate_right(18) ^ e.rotate_right(41);
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let ch = (e & f) ^ ((!e) & g);
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let t1 = s1
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.wrapping_add(ch)
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.wrapping_add(K64[i])
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.wrapping_add(w[i])
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.wrapping_add(h);
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let s0 = a.rotate_right(28) ^ a.rotate_right(34) ^ a.rotate_right(39);
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let maj = (a & b) ^ (a & c) ^ (b & c);
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let t2 = s0.wrapping_add(maj);
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h = g;
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g = f;
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f = e;
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e = d.wrapping_add(t1);
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d = c;
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c = b;
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b = a;
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a = t1.wrapping_add(t2);
40+
}
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state[0] = state[0].wrapping_add(a);
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state[1] = state[1].wrapping_add(b);
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state[2] = state[2].wrapping_add(c);
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state[3] = state[3].wrapping_add(d);
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state[4] = state[4].wrapping_add(e);
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state[5] = state[5].wrapping_add(f);
48+
state[6] = state[6].wrapping_add(g);
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state[7] = state[7].wrapping_add(h);
50+
}
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pub fn compress(state: &mut [u64; 8], blocks: &[[u8; 128]]) {
53+
for block in blocks.iter() {
54+
compress_u64(state, super::to_u64s(block));
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}
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}

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