scc

simple c99 compiler
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commit a7be835f62ea88b05cfd3ee3a31e702133d7cbd2
parent a15a20fdd53e15e9250237d2c7c9d112d5e3cd01
Author: Roberto E. Vargas Caballero <k0ga@shike2.com>
Date:   Wed, 21 Aug 2019 10:31:42 +0100

[libc] Avoid too deep recursion in qsort()

Recursing over the smaller part of the array before than
over the bigger part limits the recursion depth to
log2(n).

Diffstat:
Msrc/libc/stdlib/qsort.c | 22++++++++++++++++++----
1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/src/libc/stdlib/qsort.c b/src/libc/stdlib/qsort.c @@ -23,10 +23,15 @@ swap(char *i, char *j, size_t n) } while (--n > 0); } +/* + * This function recurses as much as log2(n) because + * it always recurses in the smaller part of the + * array. + */ static void xqsort(char *a, size_t n, struct qsort *qs) { - size_t j, es = qs->es; + size_t nj, ni, es = qs->es; char *pi, *pj, *pn; if (n <= 1) @@ -51,9 +56,18 @@ xqsort(char *a, size_t n, struct qsort *qs) } swap(a, pj, es); - j = (pj - a) / es; - xqsort(a, j, qs); - xqsort(a + (j+1)*es, n-j-1, qs); + pi = a; + ni = (pj - a) / es; + pj += es; + nj = n-nj-1; + + if (ni < nj) { + xqsort(pi, ni, qs); + xqsort(pj, nj, qs); + } else { + xqsort(pj, nj, qs); + xqsort(pi, ni, qs); + } } void