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#![no_std]
extern crate generic_array;
use generic_array::typenum::{U8, U16, U32};
use generic_array::GenericArray;
use core::mem;
const C64: u64 = 0b1_1011;
const C128: u64 = 0b1000_0111;
const C256: u64 = 0b100_0010_0101;
pub trait Dbl {
fn dbl(self) -> Self;
fn inv_dbl(self) -> Self;
}
impl Dbl for GenericArray<u8, U8> {
fn dbl(self) -> Self {
let mut val: u64 = unsafe { mem::transmute(self) };
val = val.to_be();
let a = val >> 63;
val <<= 1;
val ^= a * C64;
unsafe { mem::transmute(val.to_be()) }
}
fn inv_dbl(self) -> Self {
let mut val: u64 = unsafe { mem::transmute(self) };
val = val.to_be();
let a = val & 1;
val >>= 1;
val ^= a*((1 << 63) ^ (C64 >> 1));
unsafe { mem::transmute(val.to_be()) }
}
}
#[inline(always)]
fn to_be(val: &mut [u64]) {
for v in val.iter_mut() {
*v = v.to_be();
}
}
impl Dbl for GenericArray<u8, U16> {
fn dbl(self) -> Self {
let mut val: [u64; 2] = unsafe { mem::transmute(self) };
to_be(&mut val);
let b = val[1] >> 63;
let a = val[0] >> 63;
val[0] <<= 1;
val[0] ^= b;
val[1] <<= 1;
val[1] ^= a*C128;
to_be(&mut val);
unsafe { mem::transmute(val) }
}
fn inv_dbl(self) -> Self {
let mut val: [u64; 2] = unsafe { mem::transmute(self) };
to_be(&mut val);
let a = (val[0] & 1) << 63;
let b = val[1] & 1;
val[0] >>= 1;
val[1] >>= 1;
val[1] ^= a;
val[0] ^= b*(1 << 63);
val[1] ^= b*(C128 >> 1);
to_be(&mut val);
unsafe { mem::transmute(val) }
}
}
impl Dbl for GenericArray<u8, U32> {
fn dbl(self) -> Self {
let mut val: [u64; 4] = unsafe { mem::transmute(self) };
to_be(&mut val);
let a = val[0] >> 63;
let b = val[1] >> 63;
let c = val[2] >> 63;
let d = val[3] >> 63;
val[0] <<= 1;
val[0] ^= b;
val[1] <<= 1;
val[1] ^= c;
val[2] <<= 1;
val[2] ^= d;
val[3] <<= 1;
val[3] ^= a*C256;
to_be(&mut val);
unsafe { mem::transmute(val) }
}
fn inv_dbl(self) -> Self {
let mut val: [u64; 4] = unsafe { mem::transmute(self) };
to_be(&mut val);
let a = (val[0] & 1) << 63;
let b = (val[1] & 1) << 63;
let c = (val[2] & 1) << 63;
let d = val[3] & 1;
val[0] >>= 1;
val[1] >>= 1;
val[2] >>= 1;
val[3] >>= 1;
val[1] ^= a;
val[2] ^= b;
val[3] ^= c;
val[0] ^= d*(1 << 63);
val[3] ^= d*(C256 >> 1);
to_be(&mut val);
unsafe { mem::transmute(val) }
}
}