diff --git a/lib/stdlib/qsort.c b/lib/stdlib/qsort.c index 88655725..33aeae77 100644 --- a/lib/stdlib/qsort.c +++ b/lib/stdlib/qsort.c @@ -1,70 +1,242 @@ -/* -*-comment-start: "//";comment-end:""-*- - * GNU Mes --- Maxwell Equations of Software - * Copyright © 2017,2018 Jan (janneke) Nieuwenhuizen - * Copyright © 2021 Paul Dersey - * - * This file is part of GNU Mes. - * - * GNU Mes is free software; you can redistribute it and/or modify it - * under the terms of the GNU General Public License as published by - * the Free Software Foundation; either version 3 of the License, or (at - * your option) any later version. - * - * GNU Mes is distributed in the hope that it will be useful, but - * WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the - * GNU General Public License for more details. - * - * You should have received a copy of the GNU General Public License - * along with GNU Mes. If not, see . - */ +/* Copyright (C) 1991, 1992 Free Software Foundation, Inc. +This file is part of the GNU C Library. +Written by Douglas C. Schmidt (schmidt@ics.uci.edu). +The GNU C Library is free software; you can redistribute it and/or +modify it under the terms of the GNU Library General Public License as +published by the Free Software Foundation; either version 2 of the +License, or (at your option) any later version. + +The GNU C Library is distributed in the hope that it will be useful, +but WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +Library General Public License for more details. + +You should have received a copy of the GNU Library General Public +License along with the GNU C Library; see the file COPYING.LIB. If +not, write to the Free Software Foundation, Inc., 675 Mass Ave, +Cambridge, MA 02139, USA. */ + +#include #include #include -void -swap (void* a, void* b, int size) -{ - char buffer[size]; - memcpy (buffer, a, size); - memcpy (a, b, size); - memcpy (b, buffer, size); -} - -void -_qsort (void *base, size_t size, size_t left, size_t right, - int (*compare)(void const*, void const*)) -{ - void *vt, *v3; - int i; - int last; - int mid = (left + right) / 2; - if (left >= right) - return; - - void* vl = (char*)(base + (left * size)); - void* vr = (char*)(base + (mid * size)); - swap (vl, vr, size); - last = left; - for (i = left + 1; i <= right; i++) - { - vt = (char*)(base + (i * size)); - if ((*compare)(vl, vt) > 0) - { - ++last; - v3 = (char*)(base + (last * size)); - swap (vt, v3, size); - } - } - v3 = (char*)(base + (last * size)); - swap (vl, v3, size); - _qsort (base, size, left, last - 1, compare); - _qsort (base, size, last + 1, right, compare); -} +/* Byte-wise swap two items of size SIZE. */ +#define SWAP(a, b, size) \ + do \ + { \ + size_t __size = (size); \ + char *__a = (a), *__b = (b); \ + do \ + { \ + char __tmp = *__a; \ + *__a++ = *__b; \ + *__b++ = __tmp; \ + } while (--__size > 0); \ + } while (0) + +/* Discontinue quicksort algorithm when partition gets below this size. + This particular magic number was chosen to work best on a Sun 4/260. */ +#define MAX_THRESH 4 + +/* Stack node declarations used to store unfulfilled partition obligations. */ +typedef struct + { + char *lo; + char *hi; + } stack_node; + +/* The next 4 #defines implement a very fast in-line stack abstraction. */ +#define STACK_SIZE (8 * sizeof(unsigned long int)) +#define PUSH(low, high) ((void) ((top->lo = (low)), (top->hi = (high)), ++top)) +#define POP(low, high) ((void) (--top, (low = top->lo), (high = top->hi))) +#define STACK_NOT_EMPTY (stack < top) + + +/* Order size using quicksort. This implementation incorporates + four optimizations discussed in Sedgewick: + + 1. Non-recursive, using an explicit stack of pointer that store the + next array partition to sort. To save time, this maximum amount + of space required to store an array of MAX_INT is allocated on the + stack. Assuming a 32-bit integer, this needs only 32 * + sizeof(stack_node) == 136 bits. Pretty cheap, actually. + + 2. Chose the pivot element using a median-of-three decision tree. + This reduces the probability of selecting a bad pivot value and + eliminates certain extraneous comparisons. + + 3. Only quicksorts TOTAL_ELEMS / MAX_THRESH partitions, leaving + insertion sort to order the MAX_THRESH items within each partition. + This is a big win, since insertion sort is faster for small, mostly + sorted array segements. + + 4. The larger of the two sub-partitions is always pushed onto the + stack first, with the algorithm then concentrating on the + smaller partition. This *guarantees* no more than log (n) + stack size is needed (actually O(1) in this case)! */ void -qsort (void *base, size_t count, size_t size, - int (*compare)(void const*, void const*)) +qsort (void* base, size_t total_elems, size_t size, + int (*compare)(void const *, void const *)) { - _qsort (base, size, 0, count, compare); + char *base_ptr = (char *) base; + + /* Allocating SIZE bytes for a pivot buffer facilitates a better + algorithm below since we can do comparisons directly on the pivot. */ + char *pivot_buffer = (char *) alloca (size); + const size_t max_thresh = MAX_THRESH * size; + + if (total_elems == 0) + /* Avoid lossage with unsigned arithmetic below. */ + return; + + if (total_elems > MAX_THRESH) + { + char *lo = base_ptr; + char *hi = &lo[size * (total_elems - 1)]; + /* Largest size needed for 32-bit int!!! */ + stack_node stack[STACK_SIZE]; + stack_node *top = stack + 1; + + while (STACK_NOT_EMPTY) + { + char *left_ptr; + char *right_ptr; + + char *pivot = pivot_buffer; + + /* Select median value from among LO, MID, and HI. Rearrange + LO and HI so the three values are sorted. This lowers the + probability of picking a pathological pivot value and + skips a comparison for both the LEFT_PTR and RIGHT_PTR. */ + + char *mid = lo + size * ((hi - lo) / size >> 1); + + if ((*compare)((void*) mid, (void*) lo) < 0) + SWAP(mid, lo, size); + if ((*compare)((void*) hi, (void*) mid) < 0) + SWAP(mid, hi, size); + else + goto jump_over; + if ((*compare)((void*) mid, (void*) lo) < 0) + SWAP(mid, lo, size); + jump_over:; + memcpy(pivot, mid, size); + pivot = pivot_buffer; + + left_ptr = lo + size; + right_ptr = hi - size; + + /* Here's the famous ``collapse the walls'' section of quicksort. + Gotta like those tight inner loops! They are the main reason + that this algorithm runs much faster than others. */ + do + { + while ((*compare)((void*) left_ptr, (void*) pivot) < 0) + left_ptr += size; + + while ((*compare)((void*) pivot, (void*) right_ptr) < 0) + right_ptr -= size; + + if (left_ptr < right_ptr) + { + SWAP(left_ptr, right_ptr, size); + left_ptr += size; + right_ptr -= size; + } + else if (left_ptr == right_ptr) + { + left_ptr += size; + right_ptr -= size; + break; + } + } + while (left_ptr <= right_ptr); + + /* Set up pointers for next iteration. First determine whether + left and right partitions are below the threshold size. If so, + ignore one or both. Otherwise, push the larger partition's + bounds on the stack and continue sorting the smaller one. */ + + if ((size_t) (right_ptr - lo) <= max_thresh) + { + if ((size_t) (hi - left_ptr) <= max_thresh) + /* Ignore both small partitions. */ + POP(lo, hi); + else + /* Ignore small left partition. */ + lo = left_ptr; + } + else if ((size_t) (hi - left_ptr) <= max_thresh) + /* Ignore small right partition. */ + hi = right_ptr; + else if ((right_ptr - lo) > (hi - left_ptr)) + { + /* Push larger left partition indices. */ + PUSH(lo, right_ptr); + lo = left_ptr; + } + else + { + /* Push larger right partition indices. */ + PUSH(left_ptr, hi); + hi = right_ptr; + } + } + } + + /* Once the BASE_void* array is partially sorted by quicksort the rest + is completely sorted using insertion sort, since this is efficient + for partitions below MAX_THRESH size. BASE_void* points to the beginning + of the array to sort, and END_void* points at the very last element in + the array (*not* one beyond it!). */ + +#define min(x, y) ((x) < (y) ? (x) : (y)) + + { + char *const end_ptr = &base_ptr[size * (total_elems - 1)]; + char *tmp_ptr = base_ptr; + char *thresh = min(end_ptr, base_ptr + max_thresh); + char *run_ptr; + + /* Find smallest element in first threshold and place it at the + array's beginning. This is the smallest array element, + and the operation speeds up insertion sort's inner loop. */ + + for (run_ptr = tmp_ptr + size; run_ptr <= thresh; run_ptr += size) + if ((*compare)((void*) run_ptr, (void*) tmp_ptr) < 0) + tmp_ptr = run_ptr; + + if (tmp_ptr != base_ptr) + SWAP(tmp_ptr, base_ptr, size); + + /* Insertion sort, running from left-hand-side up to right-hand-side. */ + + run_ptr = base_ptr + size; + while ((run_ptr += size) <= end_ptr) + { + tmp_ptr = run_ptr - size; + while ((*compare)((void*) run_ptr, (void*) tmp_ptr) < 0) + tmp_ptr -= size; + + tmp_ptr += size; + if (tmp_ptr != run_ptr) + { + char *trav; + + trav = run_ptr + size; + while (--trav >= run_ptr) + { + char c = *trav; + char *hi, *lo; + + for (hi = lo = trav; (lo -= size) >= tmp_ptr; hi = lo) + *hi = *lo; + *hi = c; + } + } + } + } } +