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Add a bits() function for scalars

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Henry de Valence 2017-04-28 22:51:32 -07:00
parent 4c26ff9ccb
commit 057c84abd5
1 changed files with 12 additions and 6 deletions
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18
src/scalar.rs
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@ -207,6 +207,17 @@ impl Scalar {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ]) 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ])
} }
/// Get the bits of the scalar.
pub fn bits(&self) -> [i8;256] {
let mut bits = [0i8; 256];
for i in 0..256 {
// As i runs from 0..256, the bottom 3 bits index the bit,
// while the upper bits index the byte.
bits[i] = ((self.0[i>>3] >> (i&7)) & 1u8) as i8;
}
bits
}
/// Compute a width-5 "Non-Adjacent Form" of this scalar. /// Compute a width-5 "Non-Adjacent Form" of this scalar.
/// ///
/// A width-`w` NAF of a positive integer `k` is an expression /// A width-`w` NAF of a positive integer `k` is an expression
@ -220,12 +231,7 @@ impl Scalar {
/// nonzero coefficients are as sparse as possible. /// nonzero coefficients are as sparse as possible.
pub fn non_adjacent_form(&self) -> [i8;256] { pub fn non_adjacent_form(&self) -> [i8;256] {
// Step 1: write out bits of the scalar // Step 1: write out bits of the scalar
let mut naf = [0i8; 256]; let mut naf = self.bits();
for i in 0..256 {
// As i runs from 0..256, the bottom 3 bits index the bit,
// while the upper bits index the byte.
naf[i] = ((self.0[i>>3] >> (i&7)) & 1u8) as i8;
}
// Step 2: zero coefficients by carrying them upwards or downwards // Step 2: zero coefficients by carrying them upwards or downwards
'bits: for i in 0..256 { 'bits: for i in 0..256 {