Auto merge of #204 - koverstreet:master, r=cuviper

Minor optimization, prep work for more optimization

The patch "drop some dependencies on BigDigit's size" is the one I'd really like to get in.
This commit is contained in:
Homu 2016-07-15 15:36:44 +09:00
commit 78bad13948
1 changed files with 227 additions and 133 deletions

View File

@ -306,7 +306,8 @@ impl FromStr for BigUint {
}
}
// Read bitwise digits that evenly divide BigDigit
// Convert from a power of two radix (bits == ilog2(radix)) where bits evenly divides
// BigDigit::BITS
fn from_bitwise_digits_le(v: &[u8], bits: usize) -> BigUint {
debug_assert!(!v.is_empty() && bits <= 8 && big_digit::BITS % bits == 0);
debug_assert!(v.iter().all(|&c| (c as BigDigit) < (1 << bits)));
@ -315,14 +316,15 @@ fn from_bitwise_digits_le(v: &[u8], bits: usize) -> BigUint {
let data = v.chunks(digits_per_big_digit)
.map(|chunk| {
chunk.iter().rev().fold(0u32, |acc, &c| (acc << bits) | c as BigDigit)
chunk.iter().rev().fold(0, |acc, &c| (acc << bits) | c as BigDigit)
})
.collect();
BigUint::new(data)
}
// Read bitwise digits that don't evenly divide BigDigit
// Convert from a power of two radix (bits == ilog2(radix)) where bits doesn't evenly divide
// BigDigit::BITS
fn from_inexact_bitwise_digits_le(v: &[u8], bits: usize) -> BigUint {
debug_assert!(!v.is_empty() && bits <= 8 && big_digit::BITS % bits != 0);
debug_assert!(v.iter().all(|&c| (c as BigDigit) < (1 << bits)));
@ -331,15 +333,20 @@ fn from_inexact_bitwise_digits_le(v: &[u8], bits: usize) -> BigUint {
let mut data = Vec::with_capacity(big_digits);
let mut d = 0;
let mut dbits = 0;
let mut dbits = 0; // number of bits we currently have in d
// walk v accumululating bits in d; whenever we accumulate big_digit::BITS in d, spit out a
// big_digit:
for &c in v {
d |= (c as DoubleBigDigit) << dbits;
d |= (c as BigDigit) << dbits;
dbits += bits;
if dbits >= big_digit::BITS {
let (hi, lo) = big_digit::from_doublebigdigit(d);
data.push(lo);
d = hi as DoubleBigDigit;
data.push(d);
dbits -= big_digit::BITS;
// if dbits was > big_digit::BITS, we dropped some of the bits in c (they couldn't fit
// in d) - grab the bits we lost here:
d = (c as BigDigit) >> (bits - dbits);
}
}
@ -362,8 +369,7 @@ fn from_radix_digits_be(v: &[u8], radix: u32) -> BigUint {
let mut data = Vec::with_capacity(big_digits as usize);
let (base, power) = get_radix_base(radix);
debug_assert!(base < (1 << 32));
let base = base as BigDigit;
let radix = radix as BigDigit;
let r = v.len() % power;
let i = if r == 0 {
@ -435,7 +441,7 @@ impl Num for BigUint {
let res = if radix.is_power_of_two() {
// Powers of two can use bitwise masks and shifting instead of multiplication
let bits = radix.trailing_zeros() as usize;
let bits = ilog2(radix);
v.reverse();
if big_digit::BITS % bits == 0 {
from_bitwise_digits_le(&v, bits)
@ -1349,6 +1355,46 @@ impl Integer for BigUint {
}
}
fn high_bits_to_u64(v: &BigUint) -> u64 {
match v.data.len() {
0 => 0,
1 => v.data[0] as u64,
_ => {
let mut bits = v.bits();
let mut ret = 0u64;
let mut ret_bits = 0;
for d in v.data.iter().rev() {
let digit_bits = (bits - 1) % big_digit::BITS + 1;
let bits_want = cmp::min(64 - ret_bits, digit_bits);
if bits_want != 64 {
ret <<= bits_want;
}
ret |= *d as u64 >> (digit_bits - bits_want);
ret_bits += bits_want;
bits -= bits_want;
if ret_bits == 64 {
break;
}
}
ret
}
}
}
/// Find last set bit
/// fls(0) == 0, fls(u32::MAX) == 32
fn fls<T: traits::PrimInt>(v: T) -> usize {
std::mem::size_of::<T>() * 8 - v.leading_zeros() as usize
}
fn ilog2<T: traits::PrimInt>(v: T) -> usize {
fls(v) - 1
}
impl ToPrimitive for BigUint {
#[inline]
fn to_i64(&self) -> Option<i64> {
@ -1362,35 +1408,32 @@ impl ToPrimitive for BigUint {
})
}
// `DoubleBigDigit` size dependent
#[inline]
fn to_u64(&self) -> Option<u64> {
match self.data.len() {
0 => Some(0),
1 => Some(self.data[0] as u64),
2 => Some(big_digit::to_doublebigdigit(self.data[1], self.data[0]) as u64),
_ => None,
}
let mut ret: u64 = 0;
let mut bits = 0;
for i in self.data.iter() {
if bits >= 64 {
return None;
}
ret += (*i as u64) << bits;
bits += big_digit::BITS;
}
Some(ret)
}
// `DoubleBigDigit` size dependent
#[inline]
fn to_f32(&self) -> Option<f32> {
match self.data.len() {
0 => Some(f32::zero()),
1 => Some(self.data[0] as f32),
len => {
// this will prevent any overflow of exponent
if len > (f32::MAX_EXP as usize) / big_digit::BITS {
let mantissa = high_bits_to_u64(self);
let exponent = self.bits() - fls(mantissa);
if exponent > f32::MAX_EXP as usize {
None
} else {
let exponent = (len - 2) * big_digit::BITS;
// we need 25 significant digits, 24 to be stored and 1 for rounding
// this gives at least 33 significant digits
let mantissa = big_digit::to_doublebigdigit(self.data[len - 1],
self.data[len - 2]);
// this cast handles rounding
let ret = (mantissa as f32) * 2.0.powi(exponent as i32);
let ret = (mantissa as f32) * 2.0f32.powi(exponent as i32);
if ret.is_infinite() {
None
} else {
@ -1398,34 +1441,16 @@ impl ToPrimitive for BigUint {
}
}
}
}
}
// `DoubleBigDigit` size dependent
#[inline]
fn to_f64(&self) -> Option<f64> {
match self.data.len() {
0 => Some(f64::zero()),
1 => Some(self.data[0] as f64),
2 => Some(big_digit::to_doublebigdigit(self.data[1], self.data[0]) as f64),
len => {
// this will prevent any overflow of exponent
if len > (f64::MAX_EXP as usize) / big_digit::BITS {
let mantissa = high_bits_to_u64(self);
let exponent = self.bits() - fls(mantissa);
if exponent > f64::MAX_EXP as usize {
None
} else {
let mut exponent = (len - 2) * big_digit::BITS;
let mut mantissa = big_digit::to_doublebigdigit(self.data[len - 1],
self.data[len - 2]);
// we need at least 54 significant bit digits, 53 to be stored and 1 for rounding
// so we take enough from the next BigDigit to make it up to 64
let shift = mantissa.leading_zeros() as usize;
if shift > 0 {
mantissa <<= shift;
mantissa |= self.data[len - 3] as u64 >> (big_digit::BITS - shift);
exponent -= shift;
}
// this cast handles rounding
let ret = (mantissa as f64) * 2.0.powi(exponent as i32);
let ret = (mantissa as f64) * 2.0f64.powi(exponent as i32);
if ret.is_infinite() {
None
} else {
@ -1433,8 +1458,6 @@ impl ToPrimitive for BigUint {
}
}
}
}
}
}
impl FromPrimitive for BigUint {
@ -1484,14 +1507,17 @@ impl FromPrimitive for BigUint {
}
impl From<u64> for BigUint {
// `DoubleBigDigit` size dependent
#[inline]
fn from(n: u64) -> Self {
match big_digit::from_doublebigdigit(n) {
(0, 0) => BigUint::zero(),
(0, n0) => BigUint { data: vec![n0] },
(n1, n0) => BigUint { data: vec![n0, n1] },
fn from(mut n: u64) -> Self {
let mut ret: BigUint = Zero::zero();
while n != 0 {
ret.data.push(n as BigDigit);
// don't overflow if BITS is 64:
n = (n >> 1) >> (big_digit::BITS - 1);
}
ret
}
}
@ -1591,28 +1617,36 @@ fn to_bitwise_digits_le(u: &BigUint, bits: usize) -> Vec<u8> {
fn to_inexact_bitwise_digits_le(u: &BigUint, bits: usize) -> Vec<u8> {
debug_assert!(!u.is_zero() && bits <= 8 && big_digit::BITS % bits != 0);
let last_i = u.data.len() - 1;
let mask: DoubleBigDigit = (1 << bits) - 1;
let mask: BigDigit = (1 << bits) - 1;
let digits = (u.bits() + bits - 1) / bits;
let mut res = Vec::with_capacity(digits);
let mut r = 0;
let mut rbits = 0;
for hi in u.data[..last_i].iter().cloned() {
r |= (hi as DoubleBigDigit) << rbits;
for c in &u.data {
r |= *c << rbits;
rbits += big_digit::BITS;
while rbits >= bits {
res.push((r & mask) as u8);
r >>= bits;
// r had more bits than it could fit - grab the bits we lost
if rbits > big_digit::BITS {
r = *c >> (big_digit::BITS - (rbits - bits));
}
rbits -= bits;
}
}
r |= (u.data[last_i] as DoubleBigDigit) << rbits;
while r != 0 {
res.push((r & mask) as u8);
r >>= bits;
if rbits != 0 {
res.push(r as u8);
}
while let Some(&0) = res.last() {
res.pop();
}
res
@ -1629,8 +1663,7 @@ fn to_radix_digits_le(u: &BigUint, radix: u32) -> Vec<u8> {
let mut digits = u.clone();
let (base, power) = get_radix_base(radix);
debug_assert!(base < (1 << 32));
let base = base as BigDigit;
let radix = radix as BigDigit;
while digits.data.len() > 1 {
let (q, mut r) = div_rem_digit(digits, base);
@ -1659,7 +1692,7 @@ fn to_str_radix_reversed(u: &BigUint, radix: u32) -> Vec<u8> {
let mut res = if radix.is_power_of_two() {
// Powers of two can use bitwise masks and shifting instead of division
let bits = radix.trailing_zeros() as usize;
let bits = ilog2(radix);
if big_digit::BITS % bits == 0 {
to_bitwise_digits_le(u, bits)
} else {
@ -1852,34 +1885,46 @@ impl serde::Deserialize for BigUint {
}
}
// `DoubleBigDigit` size dependent
/// Returns the greatest power of the radix <= big_digit::BASE
#[inline]
fn get_radix_base(radix: u32) -> (DoubleBigDigit, usize) {
fn get_radix_base(radix: u32) -> (BigDigit, usize) {
debug_assert!(2 <= radix && radix <= 36, "The radix must be within 2...36");
debug_assert!(!radix.is_power_of_two());
// To generate this table:
// let target = std::u32::max as u64 + 1;
// for radix in 2u64..37 {
// let power = (target as f64).log(radix as f64) as u32;
// let base = radix.pow(power);
// let mut power = big_digit::BITS / fls(radix as u64);
// let mut base = radix.pow(power as u32);
//
// while let Some(b) = base.checked_mul(radix) {
// if b > big_digit::MAX {
// break;
// }
// base = b;
// power += 1;
// }
//
// println!("({:10}, {:2}), // {:2}", base, power, radix);
// }
const BASES: [(DoubleBigDigit, usize); 37] = [(0, 0),
(0, 0),
(4294967296, 32), // 2
(3486784401, 20), // 3
(4294967296, 16), // 4
(1220703125, 13), // 5
(2176782336, 12), // 6
(1977326743, 11), // 7
(1073741824, 10), // 8
(3486784401, 10), // 9
match big_digit::BITS {
32 => {
const BASES: [(u32, usize); 37] = [(0, 0), (0, 0),
(0, 0), // 2
(3486784401, 20),// 3
(0, 0), // 4
(1220703125, 13),// 5
(2176782336, 12),// 6
(1977326743, 11),// 7
(0, 0), // 8
(3486784401, 10),// 9
(1000000000, 9), // 10
(2357947691, 9), // 11
(429981696, 8), // 12
(815730721, 8), // 13
(1475789056, 8), // 14
(2562890625, 8), // 15
(4294967296, 8), // 16
(0, 0), // 16
(410338673, 7), // 17
(612220032, 7), // 18
(893871739, 7), // 19
@ -1895,14 +1940,60 @@ fn get_radix_base(radix: u32) -> (DoubleBigDigit, usize) {
(594823321, 6), // 29
(729000000, 6), // 30
(887503681, 6), // 31
(1073741824, 6), // 32
(0, 0), // 32
(1291467969, 6), // 33
(1544804416, 6), // 34
(1838265625, 6), // 35
(2176782336, 6) /* 36 */];
(2176782336, 6) // 36
];
assert!(2 <= radix && radix <= 36, "The radix must be within 2...36");
BASES[radix as usize]
let (base, power) = BASES[radix as usize];
(base as BigDigit, power)
}
64 => {
const BASES: [(u64, usize); 37] = [(0, 0), (0, 0),
(9223372036854775808, 63), // 2
(12157665459056928801, 40), // 3
(4611686018427387904, 31), // 4
(7450580596923828125, 27), // 5
(4738381338321616896, 24), // 6
(3909821048582988049, 22), // 7
(9223372036854775808, 21), // 8
(12157665459056928801, 20), // 9
(10000000000000000000, 19), // 10
(5559917313492231481, 18), // 11
(2218611106740436992, 17), // 12
(8650415919381337933, 17), // 13
(2177953337809371136, 16), // 14
(6568408355712890625, 16), // 15
(1152921504606846976, 15), // 16
(2862423051509815793, 15), // 17
(6746640616477458432, 15), // 18
(15181127029874798299, 15), // 19
(1638400000000000000, 14), // 20
(3243919932521508681, 14), // 21
(6221821273427820544, 14), // 22
(11592836324538749809, 14), // 23
(876488338465357824, 13), // 24
(1490116119384765625, 13), // 25
(2481152873203736576, 13), // 26
(4052555153018976267, 13), // 27
(6502111422497947648, 13), // 28
(10260628712958602189, 13), // 29
(15943230000000000000, 13), // 30
(787662783788549761, 12), // 31
(1152921504606846976, 12), // 32
(1667889514952984961, 12), // 33
(2386420683693101056, 12), // 34
(3379220508056640625, 12), // 35
(4738381338321616896, 12), // 36
];
let (base, power) = BASES[radix as usize];
(base as BigDigit, power)
}
_ => panic!("Invalid bigdigit size")
}
}
/// A Sign is a `BigInt`'s composing element.
@ -3459,8 +3550,8 @@ mod biguint_tests {
fn test_convert_i64() {
fn check(b1: BigUint, i: i64) {
let b2: BigUint = FromPrimitive::from_i64(i).unwrap();
assert!(b1 == b2);
assert!(b1.to_i64().unwrap() == i);
assert_eq!(b1, b2);
assert_eq!(b1.to_i64().unwrap(), i);
}
check(Zero::zero(), 0);
@ -3484,8 +3575,8 @@ mod biguint_tests {
fn test_convert_u64() {
fn check(b1: BigUint, u: u64) {
let b2: BigUint = FromPrimitive::from_u64(u).unwrap();
assert!(b1 == b2);
assert!(b1.to_u64().unwrap() == u);
assert_eq!(b1, b2);
assert_eq!(b1.to_u64().unwrap(), u);
}
check(Zero::zero(), 0);
@ -3976,6 +4067,7 @@ mod biguint_tests {
format!("2{}1", repeat("0").take(bits / 2 - 1).collect::<String>())),
(10,
match bits {
64 => "36893488147419103233".to_string(),
32 => "8589934593".to_string(),
16 => "131073".to_string(),
_ => panic!(),
@ -3993,12 +4085,14 @@ mod biguint_tests {
repeat("0").take(bits / 2 - 1).collect::<String>())),
(8,
match bits {
64 => "14000000000000000000004000000000000000000001".to_string(),
32 => "6000000000100000000001".to_string(),
16 => "140000400001".to_string(),
_ => panic!(),
}),
(10,
match bits {
64 => "1020847100762815390427017310442723737601".to_string(),
32 => "55340232229718589441".to_string(),
16 => "12885032961".to_string(),
_ => panic!(),