scc

simple c99 compiler
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commit 15d9bea9a00f9bc013e0a7954eb9a59fb3039549
parent 7531f49b441cafa6fc1c20659abb29bfc5f3a989
Author: Roberto E. Vargas Caballero <k0ga@shike2.com>
Date:   Fri,  8 Dec 2017 11:04:22 +0000

[lib/c] Simplify qsort()

Scc libc is not designed to be a fast library but a simple and
small library. For this reason, and after doing some testing
there is no reason to  make the code more complex.

Diffstat:
Mlib/c/src/qsort.c | 104+++++++------------------------------------------------------------------------
1 file changed, 9 insertions(+), 95 deletions(-)

diff --git a/lib/c/src/qsort.c b/lib/c/src/qsort.c @@ -5,17 +5,17 @@ /* * This implementation of qsort is based in the paper - * "Engineering a Sort Function", by Jon L.Bentley and M. Douglas McIlroy + * "Engineering a Sort Function", by Jon L.Bentley and M. Douglas McIlroy. + * A lot of different optimizations were removed to make the code simpler. */ struct qsort { size_t es; int (*cmp)(const void *, const void *); - void (*swap)(char *i, char *j, size_t n); }; static void -swapb(char *i, char *j, size_t n) +swap(char *i, char *j, size_t n) { do { char c = *i; @@ -25,88 +25,22 @@ swapb(char *i, char *j, size_t n) } static void -swapw(char *i, char *j, size_t n) -{ - int w, *wi = (int *) i, *wj = (int *) j; - - n /= sizeof(w); - - do { - w = *wi; - *wi++ = *wj; - *wj++ = w; - } while (--n > 0); -} - -static void -swapl(char *i, char *j, size_t n) -{ - char *tmp[n]; - - memcpy(tmp, i, n); - memcpy(i, j, n); - memcpy(j, tmp, n); -} - -static char * -med3(char *a, char *b, char *c, int (*cmp)(const void *, const void *)) -{ - if (cmp(a, b) < 0) { - if (cmp(b, c) < 0) - return b; - return (cmp(a, c) < 0) ? c : a; - } else { - if (cmp(b, c) > 0) - return b; - return (cmp(a, c) > 0) ? c : a; - } -} - -static char * -pivot(char *v, size_t n, struct qsort *qs) -{ - char *p1, *pm, *pn; /* 1st, middle, nth */ - int (*cmp)(const void *, const void *); - size_t s, es = qs->es; - - - pm = v + n/2 * es; - if (n < 10) - return pm; - - cmp = qs->cmp; - s = n/6 * es; - p1 = v + s; - pn = pm + 2*s; - - if (n > 50) { - s = n/8 * es; - p1 = med3(p1, p1+s, p1 + 2*s, cmp); - pm = med3(pm-s, pm, pm+s, cmp); - pn = med3(pn-2*s, pn-s, pn, cmp); - } - - return med3(p1, pm, pn, qs->cmp); -} - -static void xqsort(char *a, size_t n, struct qsort *qs) { size_t j, es = qs->es; char *pi, *pj, *pn; -tail_recursion: if (n <= 1) return; pi = a; pn = pj = a + n*es; - qs->swap(a, pivot(a, n, qs), es); + swap(a, a + n/2 * es, es); for (;;) { do { pi += es; - } while (pi < pn && qs->cmp(pi, pn) < 0); + } while (pi < pn && qs->cmp(pi, a) < 0); do { pj -= es; @@ -114,25 +48,13 @@ tail_recursion: if (pj < pi) break; - qs->swap(pi, pj, es); + swap(pi, pj, es); } - qs->swap(a, pj, es); + swap(a, pj, es); - /* - * We have to recurse over two subarrays. One of them can be - * optimized with tail recursion. We select to recurse over - * the bigger subarray, because it will allow us to apply a - * better divide and conquer strategy. - */ j = (pj - a) / es; - if (j >= n) { - xqsort(a, j, qs); - a += (j+1) * es; - } else { - xqsort(a + (j+1) * es, n-j-1, qs); - n = j; - } - goto tail_recursion; + xqsort(a, j, qs); + xqsort(a + (j+1)*es, n-j-1, qs); } void @@ -143,13 +65,5 @@ qsort(void *base, size_t nmemb, size_t size, qs.cmp = f; qs.es = size; - - if (size > 7 * sizeof(int)) - qs.swap = swapl; - else if (size % sizeof(int) == 0) - qs.swap = swapw; - else - qs.swap = swapb; - xqsort(base, nmemb, &qs); }