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Sometimes you want to find the place where an item would be in a
sorted list, whether or not it is actually there.
The BINARY_ARRAY_SEARCH_GTE macro takes an extra 'next' pointer
argument over the other binsearch macros. This will end up pointing to
the next element in the case where there is not an exact match, or
NULL when there is. That is, searching the list
{ 2, 3, 4, 4, 9}
with a standard integer compare should give the following results:
search term *result *next
1 - 2
3 3 -
4 4 [1] -
7 - 9
9 9 -
10 - - [2]
Notes
[1] There are two fours, but you will always get the first one.
[2] The both NULL case means the search term is beyond the last list
item.
You can safely use the same pointer for both 'result' and 'next', if
you don't care to distinguish between the 'greater-than' and 'equals'
cases.
There is a torture test for this.
Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>
118 lines
4.3 KiB
C
118 lines
4.3 KiB
C
/*
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Unix SMB/CIFS implementation.
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a generic binary search macro
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Copyright (C) Andrew Tridgell 2009
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef _BINSEARCH_H
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#define _BINSEARCH_H
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/* a binary array search, where the array is an array of pointers to structures,
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and we want to find a match for 'target' on 'field' in those structures.
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Inputs:
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array: base pointer to an array of structures
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arrray_size: number of elements in the array
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field: the name of the field in the structure we are keying off
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target: the field value we are looking for
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comparison_fn: the comparison function
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result: where the result of the search is put
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if the element is found, then 'result' is set to point to the found array element. If not,
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then 'result' is set to NULL.
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The array is assumed to be sorted by the same comparison_fn as the
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search (with, for example, qsort)
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*/
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#define BINARY_ARRAY_SEARCH_P(array, array_size, field, target, comparison_fn, result) do { \
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int32_t _b, _e; \
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(result) = NULL; \
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if (array_size) { for (_b = 0, _e = (array_size)-1; _b <= _e; ) { \
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int32_t _i = (_b+_e)/2; \
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int _r = comparison_fn(target, array[_i]->field); \
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if (_r == 0) { (result) = array[_i]; break; } \
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if (_r < 0) _e = _i - 1; else _b = _i + 1; \
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}} } while (0)
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/*
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like BINARY_ARRAY_SEARCH_P, but assumes that the array is an array
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of structures, rather than pointers to structures
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result points to the found structure, or NULL
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*/
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#define BINARY_ARRAY_SEARCH(array, array_size, field, target, comparison_fn, result) do { \
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int32_t _b, _e; \
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(result) = NULL; \
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if (array_size) { for (_b = 0, _e = (array_size)-1; _b <= _e; ) { \
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int32_t _i = (_b+_e)/2; \
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int _r = comparison_fn(target, array[_i].field); \
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if (_r == 0) { (result) = &array[_i]; break; } \
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if (_r < 0) _e = _i - 1; else _b = _i + 1; \
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}} } while (0)
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/*
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like BINARY_ARRAY_SEARCH_P, but assumes that the array is an array
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of elements, rather than pointers to structures
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result points to the found structure, or NULL
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*/
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#define BINARY_ARRAY_SEARCH_V(array, array_size, target, comparison_fn, result) do { \
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int32_t _b, _e; \
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(result) = NULL; \
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if (array_size) { for (_b = 0, _e = (array_size)-1; _b <= _e; ) { \
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int32_t _i = (_b+_e)/2; \
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int _r = comparison_fn(target, array[_i]); \
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if (_r == 0) { (result) = &array[_i]; break; } \
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if (_r < 0) _e = _i - 1; else _b = _i + 1; \
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}} } while (0)
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/*
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like BINARY_ARRAY_SEARCH_V, but if an exact result is not found, the 'next'
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argument will point to the element after the place where the exact result
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would have been. If an exact result is found, 'next' will be NULL. If the
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target is beyond the end of the list, both 'result' and 'next' will be NULL.
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Unlike other binsearch macros, where there are several elements that compare
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the same, the result will always point to the first one.
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If you don't care to distinguish between the 'greater than' and 'equals'
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cases, you can use the same pointer for both 'result' and 'next'.
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As with all the binsearch macros, the comparison function is always called
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with the search term first.
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*/
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#define BINARY_ARRAY_SEARCH_GTE(array, array_size, target, comparison_fn, \
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result, next) do { \
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int32_t _b, _e; \
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(result) = NULL; (next) = NULL; \
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if ((array_size) > 0) { \
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for (_b = 0, _e = (array_size)-1; _b <= _e; ) { \
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int32_t _i = (_b + _e) / 2; \
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int _r = comparison_fn(target, array[_i]); \
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if (_r == 0) { \
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(result) = &array[_i]; \
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_e = _i - 1; \
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} else if (_r < 0) { _e = _i - 1; \
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} else { _b = _i + 1; } \
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} \
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if ((result) == NULL &&_b < (array_size)) { \
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(next) = &array[_b]; \
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} } } while (0)
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#endif
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