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/* histogram/find.c
*
* Copyright (C) 1996, 1997, 1998, 1999, 2000 Brian Gough
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or (at
* your option) any later version.
*
* This program 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
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
/* determines whether to optimize for linear ranges */
#define LINEAR_OPT 1
static int find (const size_t n, const double range[],
const double x, size_t * i);
static int
find (const size_t n, const double range[], const double x, size_t * i)
{
size_t i_linear, lower, upper, mid;
if (x < range[0])
{
return -1;
}
if (x >= range[n])
{
return +1;
}
/* optimize for linear case */
#ifdef LINEAR_OPT
{
double u = (x - range[0]) / (range[n] - range[0]);
i_linear = (size_t) (u * n);
}
if (x >= range[i_linear] && x < range[i_linear + 1])
{
*i = i_linear;
return 0;
}
#endif
/* perform binary search */
upper = n ;
lower = 0 ;
while (upper - lower > 1)
{
mid = (upper + lower) / 2 ;
if (x >= range[mid])
{
lower = mid ;
}
else
{
upper = mid ;
}
}
*i = lower ;
/* sanity check the result */
if (x < range[lower] || x >= range[lower + 1])
{
GSL_ERROR ("x not found in range", GSL_ESANITY);
}
return 0;
}
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