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Add opt_size feature for embedded environments. #2

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Mar 23, 2021
Merged

Add opt_size feature for embedded environments. #2

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1 change: 1 addition & 0 deletions Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@ digest = { version = "0.9", optional = true }

[features]
default = []
opt_size = []
traits = ["digest"]

[profile.release]
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2 changes: 2 additions & 0 deletions README.md
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Expand Up @@ -5,3 +5,5 @@ A small, self-contained SHA256 and HMAC-SHA256 implementation in Rust.
Optional features:

* `traits`: enable support for the `Digest` trait from the `digest` crate.
* `opt_size`: enable size optimizations. Based on benchmarks, the `.text`
section size is reduced by 75%, at the cost of approximately 16% performance.
8 changes: 5 additions & 3 deletions src/lib.rs
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Expand Up @@ -70,7 +70,8 @@ impl W {
x.rotate_right(17) ^ x.rotate_right(19) ^ (x >> 10)
}

#[inline(always)]
#[cfg_attr(feature = "opt_size", inline(never))]
#[cfg_attr(not(feature = "opt_size"), inline(always))]
fn M(&mut self, a: usize, b: usize, c: usize, d: usize) {
let w = &mut self.0;
w[a] = w[a]
Expand Down Expand Up @@ -99,7 +100,8 @@ impl W {
self.M(15, (15 + 14) & 15, (15 + 9) & 15, (15 + 1) & 15);
}

#[inline(always)]
#[cfg_attr(feature = "opt_size", inline(never))]
#[cfg_attr(not(feature = "opt_size"), inline(always))]
fn F(&mut self, state: &mut State, i: usize, k: u32) {
let t = &mut state.0;
t[(16 - i + 7) & 7] = t[(16 - i + 7) & 7]
Expand Down Expand Up @@ -306,7 +308,7 @@ impl HMAC {
ih.update(input);

let mut oh = Hash::new();
let mut padded = [0x5c; 64];
padded = [0x5c; 64];
for (p, &k) in padded.iter_mut().zip(k2.iter()) {
*p ^= k;
}
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