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Replace old pow_with_uint with the new pow func

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There was an old and barely used implementation of pow, which expected
both parameters to be uint and required more traits to be implemented.
Since a new implementation for `pow` landed, I'm proposing to remove
this old impl in favor of the new one.

The benchmark shows that the new implementation is faster than the one
being removed:

test num::bench::bench_pow_function               ..bench:      9429 ns/iter (+/- 2055)
test num::bench::bench_pow_with_uint_function     ...bench:     28476 ns/iter (+/- 2202)
This commit is contained in:
Flavio Percoco 2014-01-18 18:10:17 +01:00
parent aaf8ba7c51
commit 3830a3b4f2
3 changed files with 8 additions and 44 deletions
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2
src/libextra/json.rs
View File

@ -688,7 +688,7 @@ impl<T : Iterator<char>> Parser<T> {
}
}
let exp: f64 = num::pow_with_uint(10u, exp);
let exp: f64 = num::pow(10u as f64, exp);
if neg_exp {
res /= exp;
} else {

37
src/libstd/num/mod.rs
View File

@ -993,37 +993,6 @@ pub fn from_str_radix<T: FromStrRadix>(str: &str, radix: uint) -> Option<T> {
FromStrRadix::from_str_radix(str, radix)
}
/// Calculates a power to a given radix, optimized for uint `pow` and `radix`.
///
/// Returns `radix^pow` as `T`.
///
/// Note:
/// Also returns `1` for `0^0`, despite that technically being an
/// undefined number. The reason for this is twofold:
/// - If code written to use this function cares about that special case, it's
/// probably going to catch it before making the call.
/// - If code written to use this function doesn't care about it, it's
/// probably assuming that `x^0` always equals `1`.
///
pub fn pow_with_uint<T:NumCast+One+Zero+Div<T,T>+Mul<T,T>>(radix: uint, pow: uint) -> T {
let _0: T = Zero::zero();
let _1: T = One::one();
if pow == 0u { return _1; }
if radix == 0u { return _0; }
let mut my_pow = pow;
let mut total = _1;
let mut multiplier = cast(radix).unwrap();
while (my_pow > 0u) {
if my_pow % 2u == 1u {
total = total * multiplier;
}
my_pow = my_pow / 2u;
multiplier = multiplier * multiplier;
}
total
}
impl<T: Zero + 'static> Zero for @T {
fn zero() -> @T { @Zero::zero() }
fn is_zero(&self) -> bool { (**self).is_zero() }
@ -1698,10 +1667,4 @@ mod bench {
let v = vec::from_fn(1024, |n| n);
b.iter(|| {v.iter().fold(0, |old, new| num::pow(old, *new));});
}
#[bench]
fn bench_pow_with_uint_function(b: &mut BenchHarness) {
let v = vec::from_fn(1024, |n| n);
b.iter(|| {v.iter().fold(0, |old, new| num::pow_with_uint(old, *new));});
}
}

13
src/libstd/num/strconv.rs
View File

@ -20,7 +20,8 @@ use str::{StrSlice};
use str;
use vec::{CopyableVector, ImmutableVector, MutableVector};
use vec::OwnedVector;
use num::{NumCast, Zero, One, cast, pow_with_uint, Integer};
use num;
use num::{NumCast, Zero, One, cast, Integer};
use num::{Round, Float, FPNaN, FPInfinite, ToPrimitive};
pub enum ExponentFormat {
@ -648,10 +649,10 @@ pub fn from_str_bytes_common<T:NumCast+Zero+One+Eq+Ord+Div<T,T>+
if exp_found {
let c = buf[i] as char;
let base = match (c, exponent) {
let base: T = match (c, exponent) {
// c is never _ so don't need to handle specially
('e', ExpDec) | ('E', ExpDec) => 10u,
('p', ExpBin) | ('P', ExpBin) => 2u,
('e', ExpDec) | ('E', ExpDec) => cast(10u).unwrap(),
('p', ExpBin) | ('P', ExpBin) => cast(2u).unwrap(),
_ => return None // char doesn't fit given exponent format
};
@ -664,9 +665,9 @@ pub fn from_str_bytes_common<T:NumCast+Zero+One+Eq+Ord+Div<T,T>+
match exp {
Some(exp_pow) => {
multiplier = if exp_pow < 0 {
_1 / pow_with_uint::<T>(base, (-exp_pow.to_int().unwrap()) as uint)
_1 / num::pow(base, (-exp_pow.to_int().unwrap()) as uint)
} else {
pow_with_uint::<T>(base, exp_pow.to_int().unwrap() as uint)
num::pow(base, exp_pow.to_int().unwrap() as uint)
}
}
None => return None // invalid exponent -> invalid number