quickfind

Quickly finds an element in a sorted list. If not found, returns -index of next smaller element.

% loc=quickfind(el,list)
%
% Finds the index of an element el in a SORTED list really quick.
% loc is the location, found is a boolean indicating whether an exact match
% was found.
%
% It doesn't check if the list is sorted, because that would take O(N) time
% and this is meant to run in O(log(N)). If you give it an unsorted list,
% it will either return a zero, and error, or the wrong answer. It is
% guaranteed to stop though, which is nice.
%
% If you give it an element that's not in the sorted list, it interpolates,
% and sets found to false.
% Special cases: if it's smaller than the first element it returns zero.
% If it's bigger then the last element it returns length(list)+1, and of
% course found will be false.
%
% Example usage
% r=sort(rand(1,10000000));
% tic, quickfind(r(7654321),r), toc
%
% Have fun..
%
% Peter
% oconnorp -at- ethz -dot- ch