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Arithmetic cleanup and optimization.

This commit is contained in:
Sean Bowe 2016-09-06 00:13:34 -06:00
parent 671d112c9c
commit 77df6c9ee5
No known key found for this signature in database
GPG Key ID: 95684257D8F8B031
1 changed files with 33 additions and 38 deletions
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71
src/arith.rs
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@ -69,13 +69,10 @@ impl U256 {
}
pub fn is_zero(&self) -> bool {
for a in self.0.iter() {
if *a != 0 {
return false;
}
}
return true;
self.0[0] == 0 &&
self.0[1] == 0 &&
self.0[2] == 0 &&
self.0[3] == 0
}
pub fn set_bit(&mut self, n: usize, to: bool)
@ -220,38 +217,41 @@ impl<'a> Iterator for BitIterator<'a> {
/// Divide by two
#[inline]
fn div2(a: &mut [u64; 4]) {
let mut b = 0;
for a in a.iter_mut().rev() {
let t = *a << 63;
*a = *a >> 1;
*a = *a | b;
b = t;
}
let mut t = a[3] << 63;
a[3] = a[3] >> 1;
let b = a[2] << 63;
a[2] >>= 1;
a[2] |= t;
t = a[1] << 63;
a[1] >>= 1;
a[1] |= b;
a[0] >>= 1;
a[0] |= t;
}
#[inline]
#[inline(always)]
fn split_u64(i: u64) -> (u64, u64) {
(i >> 32, i & 0xFFFFFFFF)
}
#[inline]
#[inline(always)]
fn combine_u64(hi: u64, lo: u64) -> u64 {
(hi << 32) | lo
}
#[inline]
fn adc(a: u64, b: u64, carry: &mut u64) -> u64 {
let (a1, a0) = split_u64(a);
let (b1, b0) = split_u64(b);
let (c, r0) = split_u64(a0 + b0 + *carry);
let (c, r1) = split_u64(a1 + b1 + c);
*carry = c;
combine_u64(r1, r0)
}
#[inline]
fn add_nocarry(a: &mut [u64; 4], b: &[u64; 4]) {
#[inline]
fn adc(a: u64, b: u64, carry: &mut u64) -> u64 {
let (a1, a0) = split_u64(a);
let (b1, b0) = split_u64(b);
let (c, r0) = split_u64(a0 + b0 + *carry);
let (c, r1) = split_u64(a1 + b1 + c);
*carry = c;
combine_u64(r1, r0)
}
let mut carry = 0;
for (a, b) in a.into_iter().zip(b.iter()) {
@ -299,21 +299,16 @@ fn mul_reduce(
let (b_hi, b_lo) = split_u64(b);
let (c_hi, c_lo) = split_u64(c);
let (x_hi, x_lo) = split_u64(b_lo * c_lo);
let (a_hi, a_lo) = split_u64(a);
let (carry_hi, carry_lo) = split_u64(*carry);
let (x_hi, x_lo) = split_u64(b_lo * c_lo + a_lo + carry_lo);
let (y_hi, y_lo) = split_u64(b_lo * c_hi);
let (z_hi, z_lo) = split_u64(b_hi * c_lo);
let (r_hi, r_lo) = split_u64(x_hi + y_lo + z_lo);
let mut c0 = (r_lo << 32) | x_lo;
let mut c1 = (b_hi * c_hi) + r_hi + y_hi + z_hi;
let (r_hi, r_lo) = split_u64(x_hi + y_lo + z_lo + a_hi + carry_hi);
let mut c = 0;
c0 = adc(c0, *carry, &mut c);
c1 = adc(c1, 0, &mut c);
c0 = adc(c0, a, &mut c);
c1 = adc(c1, 0, &mut c);
*carry = (b_hi * c_hi) + r_hi + y_hi + z_hi;
*carry = c1;
c0
combine_u64(r_lo, x_lo)
}
if c == 0 {