diff options
Diffstat (limited to 'stdlib')
-rw-r--r-- | stdlib/qsort.c | 208 | ||||
-rw-r--r-- | stdlib/qsort_common.c | 225 |
2 files changed, 233 insertions, 200 deletions
diff --git a/stdlib/qsort.c b/stdlib/qsort.c index c3fb0e862f..10b805930a 100644 --- a/stdlib/qsort.c +++ b/stdlib/qsort.c @@ -16,17 +16,13 @@ License along with the GNU C Library; if not, see <http://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. */ - #include <limits.h> #include <stdlib.h> #include <string.h> #include <stdbool.h> -/* Swap SIZE bytes between addresses A and B. Helper to generic types - are provided as an optimization. */ +/* Swap SIZE bytes between addresses A and B. These helpers are provided + along the generic one as an optimization. */ typedef void (*swap_t)(void *, void *, size_t); @@ -104,202 +100,14 @@ typedef struct #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 -__qsort_r (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; - - swap_t swap = select_swap_func (pbase, size); - - 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; - } - } - } - } -} +#define R_VERSION +#define R_FUNC __qsort_r +#include <stdlib/qsort_common.c> libc_hidden_def (__qsort_r) weak_alias (__qsort_r, qsort_r) -void -qsort (void *b, size_t n, size_t s, __compar_fn_t cmp) -{ - return __qsort_r (b, n, s, (__compar_d_fn_t) cmp, NULL); -} +#define R_FUNC qsort +#include <stdlib/qsort_common.c> + libc_hidden_def (qsort) diff --git a/stdlib/qsort_common.c b/stdlib/qsort_common.c new file mode 100644 index 0000000000..666b1958ab --- /dev/null +++ b/stdlib/qsort_common.c @@ -0,0 +1,225 @@ +/* Common implementation for both qsort and qsort_r. + Copyright (C) 2018 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + 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 + <http://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. */ + +#ifdef R_VERSION +# define R_CMP_TYPE __compar_d_fn_t +# define R_CMP_ARG , void *arg +# define R_CMP(p1, p2) cmp (p1, p2, arg) +#else +# define R_CMP_TYPE __compar_fn_t +# define R_CMP_ARG +# define R_CMP(p1, p2) cmp (p1, p2) +#endif + +/* 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 +R_FUNC (void *pbase, size_t total_elems, size_t size, R_CMP_TYPE cmp R_CMP_ARG) +{ + if (total_elems == 0) + /* Avoid lossage with unsigned arithmetic below. */ + return; + + char *base_ptr = (char *) pbase; + + const size_t max_thresh = MAX_THRESH * size; + + swap_t swap = select_swap_func (pbase, size); + + 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 (R_CMP ((void *) mid, (void *) lo) < 0) + swap (mid, lo, size); + if (R_CMP ((void *) hi, (void *) mid) < 0) + swap (mid, hi, size); + else + goto jump_over; + if (R_CMP ((void *) mid, (void *) lo) < 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 (R_CMP ((void *) left_ptr, (void *) mid) < 0) + left_ptr += size; + + while (R_CMP ((void *) mid, (void *) right_ptr) < 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!). */ + + { + char *const end_ptr = &base_ptr[size * (total_elems - 1)]; + char *tmp_ptr = base_ptr; + char *thresh = end_ptr < base_ptr + max_thresh ? + 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 (R_CMP ((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 (R_CMP ((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; + } + } + } + } +} + +#undef R_NAME +#undef R_CMP_TYPE +#undef R_CMP_ARG +#undef R_CMP +#undef R_FUNC +#undef R_VERSION |