1   /* Copyright 2022-2025 Thales Alenia Space
2    * Licensed to CS GROUP (CS) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * CS licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *   http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.orekit.gnss.rflink.gps;
18  
19  import org.hipparchus.util.MathUtils;
20  
21  /**
22   * Container for sub-frames 4, page 25.
23   * <p>
24   * Table 20-1, sheet 9 and table 40-1, sheet 9 in
25   * <a href="https://navcen.uscg.gov/sites/default/files/pdf/gps/IS-GPS-200N.pdf">NAVSTAR
26   * GPS Space Segment/Navigation User Segment Interface</a>, IS-GPS-200N, 22 Aug 2022
27   * </p>
28   * @author Luc Maisonobe
29   * @since 12.0
30   */
31  public class SubFrame4E extends SubFrame45 {
32  
33      /** Number of Anti-spoofing entries. */
34      public static final int NB_AS = 32;
35  
36      /** Number of SV health entries. */
37      public static final int NB_SVH = 8;
38  
39      /** Size of Anti-spoofing. */
40      private static final int AS_SIZE = 4;
41  
42      /** Size of SV Health. */
43      private static final int SVH_SIZE = 6;
44  
45      /** Index of first AS field. */
46      private static final int FIRST_AS = 9;
47  
48      /** Index of reserved field in word 8. */
49      private static final int RESERVED_8 = FIRST_AS + NB_AS;
50  
51      /** Index of reserved field in word 10. */
52      private static final int RESERVED_10 = RESERVED_8 + 1 + NB_AS + NB_SVH;
53  
54      /** Simple constructor.
55       * @param words raw words
56       */
57      SubFrame4E(final int[] words) {
58  
59          // create raw container
60          super(words, RESERVED_10 + 1);
61  
62          // populate container
63          int field = FIRST_AS - 1;
64          int word  = 3;
65          int shift = 22;
66  
67          // anti-spoofing
68          for (int i = 0; i < NB_AS; ++i) {
69              if (shift >= AS_SIZE + PARITY_SIZE) {
70                  // current word contains a complete AS
71                  shift -= AS_SIZE;
72                  setField(++field, word, shift, AS_SIZE, words);
73              } else {
74                  // current word is exhausted
75                  shift = WORD_SIZE - AS_SIZE;
76                  setField(++field, ++word, shift, AS_SIZE, words);
77              }
78          }
79  
80          // 2 bits for system use
81          shift -= 2;
82          setField(RESERVED_8, word, shift, 2, words);
83  
84          // SV health
85          for (int i = 0; i < NB_SVH; ++i) {
86              if (shift >= SVH_SIZE + PARITY_SIZE) {
87                  // current word contains a complete SVH
88                  shift -= SVH_SIZE;
89                  setField(++field, word, shift, SVH_SIZE, words);
90              } else {
91                  // current word is exhausted
92                  shift = WORD_SIZE - SVH_SIZE;
93                  setField(++field, ++word, shift, SVH_SIZE, words);
94              }
95          }
96  
97          setField(RESERVED_10, 10,  8, 4, words);
98  
99      }
100 
101     /** Get the anti-spoofing for a satellite.
102      * @param index in the sub-frame (from 1 to 32, beware it is not the satellite number,
103      * it is also related to {@link #getDataId()})
104      * @return anti-spoofing
105      */
106     public int getAntiSpoofing(final int index) {
107         MathUtils.checkRangeInclusive(index, 1, NB_AS);
108         return getField(FIRST_AS + index - 1);
109     }
110 
111     /** Get the reserved field in word 8.
112      * @return reserved field in word 8
113      */
114     public int getReserved8() {
115         return getField(RESERVED_8);
116     }
117 
118     /** Get the Sv health for a satellite.
119      * @param index in the sub-frame (from 1 to 7 or 1 to 8 depending on
120      * {@link #getDataId()}, beware it is not the satellite number,
121      * it is also related to {@link #getDataId()}), an
122      * @return anti-spoofing
123      */
124     public int getSvHealth(final int index) {
125         MathUtils.checkRangeInclusive(index, 1, NB_SVH);
126         return getField(RESERVED_8 + index);
127     }
128 
129     /** Get the reserved field in word 10.
130      * @return reserved field in word 10
131      */
132     public int getReserved10() {
133         return getField(RESERVED_10);
134     }
135 
136 }