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std: Make merge_sort faster

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This commit is contained in:
Brian Anderson 2012-02-27 18:32:45 -08:00
commit 61691c2428
1 changed files with 27 additions and 15 deletions
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42
src/libstd/sort.rs
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@ -3,7 +3,7 @@ Module: sort
Sorting methods
*/
import vec::{len, slice};
import vec::len;
export merge_sort;
export quick_sort;
@ -21,29 +21,41 @@ Has worst case O(n log n) performance, best case O(n), but
is not space efficient. This is a stable sort.
*/
fn merge_sort<T: copy>(le: le<T>, v: [const T]) -> [T] {
type slice = (uint, uint);
ret merge_sort_(le, v, (0u, len(v)));
fn merge_sort_<T: copy>(le: le<T>, v: [const T], slice: slice) -> [T] {
let begin = tuple::first(slice);
let end = tuple::second(slice);
let v_len = end - begin;
if v_len == 0u { ret []; }
if v_len == 1u { ret [v[begin]]; }
let mid = v_len / 2u + begin;
let a = (begin, mid);
let b = (mid, end);
ret merge(le, merge_sort_(le, v, a), merge_sort_(le, v, b));
}
fn merge<T: copy>(le: le<T>, a: [T], b: [T]) -> [T] {
let rs: [T] = [];
let a_len: uint = len::<T>(a);
let a_ix: uint = 0u;
let b_len: uint = len::<T>(b);
let b_ix: uint = 0u;
let rs = [];
vec::reserve(rs, len(a) + len(b));
let a_len = len(a);
let a_ix = 0u;
let b_len = len(b);
let b_ix = 0u;
while a_ix < a_len && b_ix < b_len {
if le(a[a_ix], b[b_ix]) {
rs += [a[a_ix]];
a_ix += 1u;
} else { rs += [b[b_ix]]; b_ix += 1u; }
}
rs += slice::<T>(a, a_ix, a_len);
rs += slice::<T>(b, b_ix, b_len);
rs += vec::slice(a, a_ix, a_len);
rs += vec::slice(b, b_ix, b_len);
ret rs;
}
let v_len: uint = len::<T>(v);
if v_len == 0u { ret []; }
if v_len == 1u { ret [v[0]]; }
let mid: uint = v_len / 2u;
let a: [T] = slice::<T>(v, 0u, mid);
let b: [T] = slice::<T>(v, mid, v_len);
ret merge::<T>(le, merge_sort::<T>(le, a), merge_sort::<T>(le, b));
}
fn part<T: copy>(compare_func: le<T>, arr: [mutable T], left: uint,