sqrt.c 2.01 KB
Newer Older
1 2 3 4 5
/*
 * Licensed to the OpenAirInterface (OAI) Software Alliance under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The OpenAirInterface Software Alliance licenses this file to You under
6
 * the OAI Public License, Version 1.1  (the "License"); you may not use this file
7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
 * except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.openairinterface.org/?page_id=698
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *-------------------------------------------------------------------------------
 * For more information about the OpenAirInterface (OAI) Software Alliance:
 *      contact@openairinterface.org
 */

22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
//----------------------------------------------
//
// Integer square root. Take the square root of an integer.
//

#define step(shift) \
    if((0x40000000l >> shift) + root <= value)          \
    {                                                   \
        value -= (0x40000000l >> shift) + root;         \
        root = (root >> 1) | (0x40000000l >> shift);    \
    }                                                   \
    else                                                \
    {                                                   \
        root = root >> 1;                               \
    }

38
int
39 40
iSqrt(int value)
{
41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64
  int root = 0;

  step( 0);
  step( 2);
  step( 4);
  step( 6);
  step( 8);
  step(10);
  step(12);
  step(14);
  step(16);
  step(18);
  step(20);
  step(22);
  step(24);
  step(26);
  step(28);
  step(30);

  // round to the nearest integer, cuts max error in half

  if(root < value) {
    ++root;
  }
65

66
  return root;
67 68 69 70
}