Retro68/Samples/Raytracer/fixed.cc

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/*
Copyright 2012 Wolfgang Thaller.
This file is part of Retro68.
Retro68 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 3 of the License, or
(at your option) any later version.
Retro68 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 Retro68. If not, see <http://www.gnu.org/licenses/>.
*/
#include "fixed.h"
long fixed::nMul = 0, fixed::nIMul = 0, fixed::nDiv = 0, fixed::nSqrt = 0;
fixed sqrt(fixed f)
{
COUNT_OP(fixed::nSqrt);
const int FRACBITS = 16; /* Must be even! */
const int ITERS = 15 + (FRACBITS >> 1);
unsigned long root, remHi, remLo, testDiv, count;
root = 0; /* Clear root */
remHi = 0; /* Clear high part of partial remainder */
remLo = f.val; /* Get argument into low part of partial remainder */
count = ITERS; /* Load loop counter */
do {
remHi = (remHi << 2) | (remLo >> 30); remLo <<= 2; /* get 2 bits of arg */
root <<= 1; /* Get ready for the next bit in the root */
testDiv = (root << 1) + 1; /* Test radical */
if (remHi >= testDiv) {
remHi -= testDiv;
root += 1;
}
} while (count-- != 0);
return fixed(root, fixed::raw());
}