num: Slightly optimize bigint
This commit is contained in:
Florian Zeitz
parent
5cd17b8150
commit
f496ab6a6f
@ -47,6 +47,7 @@ A `BigDigit` is half the size of machine word size.
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pub type BigDigit = u32;
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pub static ZERO_BIG_DIGIT: BigDigit = 0;
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static ZERO_VEC: [BigDigit, ..1] = [ZERO_BIG_DIGIT];
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pub mod BigDigit {
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use super::BigDigit;
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@ -140,37 +141,28 @@ impl Num for BigUint {}
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impl BitAnd<BigUint, BigUint> for BigUint {
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fn bitand(&self, other: &BigUint) -> BigUint {
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let new_len = cmp::min(self.data.len(), other.data.len());
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let anded = vec::from_fn(new_len, |i| {
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// i will never be less than the size of either data vector
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let ai = self.data[i];
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let bi = other.data[i];
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ai & bi
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});
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return BigUint::new(anded);
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BigUint::new(self.data.iter().zip(other.data.iter()).map(|(ai, bi)| *ai & *bi).collect())
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}
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}
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impl BitOr<BigUint, BigUint> for BigUint {
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fn bitor(&self, other: &BigUint) -> BigUint {
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let new_len = cmp::max(self.data.len(), other.data.len());
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let ored = vec::from_fn(new_len, |i| {
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let ai = if i < self.data.len() { self.data[i] } else { 0 };
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let bi = if i < other.data.len() { other.data[i] } else { 0 };
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ai | bi
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});
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let zeros = ZERO_VEC.iter().cycle();
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let (a, b) = if self.data.len() > other.data.len() { (self, other) } else { (other, self) };
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let ored = a.data.iter().zip(b.data.iter().chain(zeros)).map(
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|(ai, bi)| *ai | *bi
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).collect();
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return BigUint::new(ored);
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}
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}
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impl BitXor<BigUint, BigUint> for BigUint {
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fn bitxor(&self, other: &BigUint) -> BigUint {
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let new_len = cmp::max(self.data.len(), other.data.len());
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let xored = vec::from_fn(new_len, |i| {
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let ai = if i < self.data.len() { self.data[i] } else { 0 };
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let bi = if i < other.data.len() { other.data[i] } else { 0 };
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ai ^ bi
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});
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let zeros = ZERO_VEC.iter().cycle();
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let (a, b) = if self.data.len() > other.data.len() { (self, other) } else { (other, self) };
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let xored = a.data.iter().zip(b.data.iter().chain(zeros)).map(
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|(ai, bi)| *ai ^ *bi
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).collect();
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return BigUint::new(xored);
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}
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}
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@ -210,18 +202,15 @@ impl Unsigned for BigUint {}
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impl Add<BigUint, BigUint> for BigUint {
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fn add(&self, other: &BigUint) -> BigUint {
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let new_len = cmp::max(self.data.len(), other.data.len());
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let zeros = ZERO_VEC.iter().cycle();
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let (a, b) = if self.data.len() > other.data.len() { (self, other) } else { (other, self) };
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let mut carry = 0;
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let mut sum = vec::from_fn(new_len, |i| {
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let ai = if i < self.data.len() { self.data[i] } else { 0 };
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let bi = if i < other.data.len() { other.data[i] } else { 0 };
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let (hi, lo) = BigDigit::from_uint(
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(ai as uint) + (bi as uint) + (carry as uint)
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);
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let mut sum: ~[BigDigit] = a.data.iter().zip(b.data.iter().chain(zeros)).map(|(ai, bi)| {
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let (hi, lo) = BigDigit::from_uint((*ai as uint) + (*bi as uint) + (carry as uint));
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carry = hi;
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lo
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});
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}).collect();
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if carry != 0 { sum.push(carry); }
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return BigUint::new(sum);
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}
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@ -230,14 +219,13 @@ impl Add<BigUint, BigUint> for BigUint {
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impl Sub<BigUint, BigUint> for BigUint {
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fn sub(&self, other: &BigUint) -> BigUint {
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let new_len = cmp::max(self.data.len(), other.data.len());
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let zeros = ZERO_VEC.iter().cycle();
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let (a, b) = (self.data.iter().chain(zeros.clone()), other.data.iter().chain(zeros));
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let mut borrow = 0;
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let diff = vec::from_fn(new_len, |i| {
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let ai = if i < self.data.len() { self.data[i] } else { 0 };
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let bi = if i < other.data.len() { other.data[i] } else { 0 };
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let diff: ~[BigDigit] = a.take(new_len).zip(b).map(|(ai, bi)| {
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let (hi, lo) = BigDigit::from_uint(
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(BigDigit::base) +
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(ai as uint) - (bi as uint) - (borrow as uint)
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BigDigit::base + (*ai as uint) - (*bi as uint) - (borrow as uint)
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);
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/*
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hi * (base) + lo == 1*(base) + ai - bi - borrow
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@ -245,7 +233,7 @@ impl Sub<BigUint, BigUint> for BigUint {
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*/
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borrow = if hi == 0 { 1 } else { 0 };
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lo
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});
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}).collect();
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assert_eq!(borrow, 0); // <=> assert!((self >= other));
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return BigUint::new(diff);
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@ -451,17 +439,18 @@ impl Integer for BigUint {
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return (Zero::zero(), Zero::zero(), (*a).clone());
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}
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let an = a.data.slice(a.data.len() - n, a.data.len());
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let an = a.data.tailn(a.data.len() - n);
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let bn = *b.data.last().unwrap();
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let mut d = ~[];
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let mut d = vec::with_capacity(an.len());
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let mut carry = 0;
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for elt in an.rev_iter() {
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let ai = BigDigit::to_uint(carry, *elt);
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let di = ai / (bn as uint);
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assert!(di < BigDigit::base);
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carry = (ai % (bn as uint)) as BigDigit;
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d = ~[di as BigDigit] + d;
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d.push(di as BigDigit)
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}
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d.reverse();
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let shift = (a.data.len() - an.len()) - (b.data.len() - 1);
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if shift == 0 {
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@ -506,10 +495,9 @@ impl Integer for BigUint {
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#[inline]
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fn is_even(&self) -> bool {
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// Considering only the last digit.
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if self.data.is_empty() {
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true
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} else {
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self.data[0].is_even()
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match self.data.head() {
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Some(x) => x.is_even(),
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None => true
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}
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}
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@ -664,12 +652,12 @@ impl ToStrRadix for BigUint {
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if base == BigDigit::base {
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return fill_concat(self.data, radix, max_len)
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}
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return fill_concat(convert_base((*self).clone(), base), radix, max_len);
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return fill_concat(convert_base(self, base), radix, max_len);
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fn convert_base(n: BigUint, base: uint) -> ~[BigDigit] {
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fn convert_base(n: &BigUint, base: uint) -> ~[BigDigit] {
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let divider = FromPrimitive::from_uint(base).unwrap();
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let mut result = ~[];
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let mut m = n;
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let mut m = n.clone();
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while m >= divider {
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let (d, m0) = m.div_mod_floor(÷r);
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result.push(m0.to_uint().unwrap() as BigDigit);
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