| /* Copyright (C) 1991-2023 Free Software Foundation, Inc. |
| This file is part of libctf (imported from Gnulib). |
| 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 Lesser General Public |
| License as published by the Free Software Foundation; either |
| version 2.1 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 |
| Lesser General Public License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public |
| License along with the GNU C Library; if not, see |
| <https://www.gnu.org/licenses/>. */ |
| |
| /* If you consider tuning this algorithm, you should consult first: |
| Engineering a sort function; Jon Bentley and M. Douglas McIlroy; |
| Software - Practice and Experience; Vol. 23 (11), 1249-1265, 1993. */ |
| |
| #ifndef _LIBC |
| # include <config.h> |
| #endif |
| |
| #include <limits.h> |
| #include <stdlib.h> |
| #include <string.h> |
| #include "ctf-decls.h" |
| |
| #ifndef _LIBC |
| # define _quicksort ctf_qsort_r |
| # define __compar_d_fn_t compar_d_fn_t |
| typedef int (*compar_d_fn_t) (const void *, const void *, void *); |
| #endif |
| |
| /* 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. */ |
| /* The stack needs log (total_elements) entries (we could even subtract |
| log(MAX_THRESH)). Since total_elements has type size_t, we get as |
| upper bound for log (total_elements): |
| bits per byte (CHAR_BIT) * sizeof(size_t). */ |
| #define STACK_SIZE (CHAR_BIT * sizeof(size_t)) |
| #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 SIZE_MAX is allocated on the |
| stack. Assuming a 32-bit (64 bit) integer for size_t, this needs |
| only 32 * sizeof(stack_node) == 256 bytes (for 64 bit: 1024 bytes). |
| 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 segments. |
| |
| 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 (total_elems) |
| stack size is needed (actually O(1) in this case)! */ |
| |
| void |
| _quicksort (void *const pbase, size_t total_elems, size_t size, |
| __compar_d_fn_t cmp, void *arg) |
| { |
| char *base_ptr = (char *) pbase; |
| |
| 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)]; |
| stack_node stack[STACK_SIZE]; |
| stack_node *top = stack; |
| |
| PUSH (NULL, NULL); |
| |
| while (STACK_NOT_EMPTY) |
| { |
| char *left_ptr; |
| char *right_ptr; |
| |
| /* 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 in |
| the while loops. */ |
| |
| char *mid = lo + size * ((hi - lo) / size >> 1); |
| |
| if ((*cmp) ((void *) mid, (void *) lo, arg) < 0) |
| SWAP (mid, lo, size); |
| if ((*cmp) ((void *) hi, (void *) mid, arg) < 0) |
| SWAP (mid, hi, size); |
| else |
| goto jump_over; |
| if ((*cmp) ((void *) mid, (void *) lo, arg) < 0) |
| SWAP (mid, lo, size); |
| jump_over:; |
| |
| 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 ((*cmp) ((void *) left_ptr, (void *) mid, arg) < 0) |
| left_ptr += size; |
| |
| while ((*cmp) ((void *) mid, (void *) right_ptr, arg) < 0) |
| right_ptr -= size; |
| |
| if (left_ptr < right_ptr) |
| { |
| SWAP (left_ptr, right_ptr, size); |
| if (mid == left_ptr) |
| mid = right_ptr; |
| else if (mid == right_ptr) |
| mid = left_ptr; |
| 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_PTR 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_PTR points to the beginning |
| of the array to sort, and END_PTR 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 ((*cmp) ((void *) run_ptr, (void *) tmp_ptr, arg) < 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 ((*cmp) ((void *) run_ptr, (void *) tmp_ptr, arg) < 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; |
| } |
| } |
| } |
| } |
| } |