From 4d3ac1c0dcd34e53f11a60888eda65dc73d78de4 Mon Sep 17 00:00:00 2001
From: Alex Lyon <arcterus@mail.com>
Date: Sun, 13 May 2018 03:29:53 -0700
Subject: [PATCH] stdlib: save stack space by looping in introsort_helper()
---
src/stdlib/src/sort.rs | 34 +++++++++++++++++++++-------------
1 file changed, 21 insertions(+), 13 deletions(-)
diff --git a/src/stdlib/src/sort.rs b/src/stdlib/src/sort.rs
index bbcd9fb1..79d1e948 100644
--- a/src/stdlib/src/sort.rs
+++ b/src/stdlib/src/sort.rs
@@ -25,24 +25,32 @@ fn log2(num: size_t) -> size_t {
}
fn introsort_helper(
- base: *mut c_char,
- nel: size_t,
+ mut base: *mut c_char,
+ mut nel: size_t,
width: size_t,
- maxdepth: size_t,
+ mut maxdepth: size_t,
comp: extern "C" fn(*const c_void, *const c_void) -> c_int,
) {
const THRESHOLD: size_t = 8;
- if nel < THRESHOLD {
- insertion_sort(base, nel, width, comp);
- } else if nel > 1 {
- if maxdepth == 0 {
- heapsort(base, nel, width, comp);
- } else {
- let (left, right) = partition(base, nel, width, comp);
- introsort_helper(base, left, width, maxdepth, comp);
- let right_base = unsafe { base.add((right + 1) * width) };
- introsort_helper(right_base, nel - (right + 1), width, maxdepth - 1, comp);
+ // this loop is a trick to save stack space because TCO is not a thing in Rustland
+ // basically, we just change the arguments and loop rather than recursing for the second call
+ // to introsort_helper()
+ loop {
+ if nel < THRESHOLD {
+ insertion_sort(base, nel, width, comp);
+ break;
+ } else if nel > 1 {
+ if maxdepth == 0 {
+ heapsort(base, nel, width, comp);
+ break;
+ } else {
+ let (left, right) = partition(base, nel, width, comp);
+ introsort_helper(base, left, width, maxdepth, comp);
+ base = unsafe { base.add((right + 1) * width) };
+ nel -= right + 1;
+ maxdepth -= 1;
+ }
}
}
}
--
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