/* | |

* Copyright (c) 1990 Regents of the University of California. | |

* All rights reserved. | |

* | |

* Redistribution and use in source and binary forms, with or without | |

* modification, are permitted provided that the following conditions | |

* are met: | |

* 1. Redistributions of source code must retain the above copyright | |

* notice, this list of conditions and the following disclaimer. | |

* 2. Redistributions in binary form must reproduce the above copyright | |

* notice, this list of conditions and the following disclaimer in the | |

* documentation and/or other materials provided with the distribution. | |

* 3. [rescinded 22 July 1999] | |

* 4. Neither the name of the University nor the names of its contributors | |

* may be used to endorse or promote products derived from this software | |

* without specific prior written permission. | |

* | |

* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | |

* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |

* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |

* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE | |

* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |

* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |

* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |

* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |

* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |

* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |

* SUCH DAMAGE. | |

*/ | |

/* | |

@deftypefn Supplemental void* bsearch (const void *@var{key}, @ | |

const void *@var{base}, size_t @var{nmemb}, size_t @var{size}, @ | |

int (*@var{compar})(const void *, const void *)) | |

Performs a search over an array of @var{nmemb} elements pointed to by | |

@var{base} for a member that matches the object pointed to by @var{key}. | |

The size of each member is specified by @var{size}. The array contents | |

should be sorted in ascending order according to the @var{compar} | |

comparison function. This routine should take two arguments pointing to | |

the @var{key} and to an array member, in that order, and should return an | |

integer less than, equal to, or greater than zero if the @var{key} object | |

is respectively less than, matching, or greater than the array member. | |

@end deftypefn | |

*/ | |

#include "config.h" | |

#include "ansidecl.h" | |

#include <sys/types.h> /* size_t */ | |

#include <stdio.h> | |

/* | |

* Perform a binary search. | |

* | |

* The code below is a bit sneaky. After a comparison fails, we | |

* divide the work in half by moving either left or right. If lim | |

* is odd, moving left simply involves halving lim: e.g., when lim | |

* is 5 we look at item 2, so we change lim to 2 so that we will | |

* look at items 0 & 1. If lim is even, the same applies. If lim | |

* is odd, moving right again involes halving lim, this time moving | |

* the base up one item past p: e.g., when lim is 5 we change base | |

* to item 3 and make lim 2 so that we will look at items 3 and 4. | |

* If lim is even, however, we have to shrink it by one before | |

* halving: e.g., when lim is 4, we still looked at item 2, so we | |

* have to make lim 3, then halve, obtaining 1, so that we will only | |

* look at item 3. | |

*/ | |

void * | |

bsearch (register const void *key, const void *base0, | |

size_t nmemb, register size_t size, | |

register int (*compar)(const void *, const void *)) | |

{ | |

register const char *base = (const char *) base0; | |

register int lim, cmp; | |

register const void *p; | |

for (lim = nmemb; lim != 0; lim >>= 1) { | |

p = base + (lim >> 1) * size; | |

cmp = (*compar)(key, p); | |

if (cmp == 0) | |

return (void *)p; | |

if (cmp > 0) { /* key > p: move right */ | |

base = (const char *)p + size; | |

lim--; | |

} /* else move left */ | |

} | |

return (NULL); | |

} |