1 /******************************************************************************
2  *
3  * Copyright (C) 2015 The Android Open Source Project
4  *
5  * Licensed under the Apache License, Version 2.0 (the "License");
6  * you may not use this file except in compliance with the License.
7  * 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  *****************************************************************************
18  * Originally developed and contributed by Ittiam Systems Pvt. Ltd, Bangalore
19 */
20 /**
21 *******************************************************************************
22 * @file
23 *  icv_variance.c
24 *
25 * @brief
26 *  This file contains the functions to compute variance
27 *
28 * @author
29 *  Ittiam
30 *
31 * @par List of Functions:
32 *  icv_variance_8x4()
33 *
34 * @remarks
35 *  None
36 *
37 *******************************************************************************
38 */
39 /*****************************************************************************/
40 /* File Includes                                                             */
41 /*****************************************************************************/
42 /* System include files */
43 #include <stdio.h>
44 #include <stdint.h>
45 #include <string.h>
46 #include <stdlib.h>
47 #include <assert.h>
48 
49 
50 /* User include files */
51 #include "icv_datatypes.h"
52 #include "icv_macros.h"
53 #include "icv_platform_macros.h"
54 #include "icv.h"
55 
56 /**
57 *******************************************************************************
58 *
59 * @brief
60 *  Computes variance of a given 8x4 block
61 *
62 * @par   Description
63 *  Compute variance of a given 8x4 block
64 *
65 * @param[in] pu1_src
66 *  Source
67 *
68 * @param[in] src_strd
69 *  Source stride
70 *
71 * @param[in] wd
72 *  Assumed to be 8
73 *
74 * @param[in] ht
75 *  Assumed to be 4
76 *
77 * @returns
78 *  Variance
79 *
80 * @remarks
81 *
82 *******************************************************************************
83 */
84 WORD32 icv_variance_8x4(UWORD8 *pu1_src, WORD32 src_strd, WORD32 wd, WORD32 ht)
85 {
86     WORD32 sum;
87     WORD32 sum_sqr;
88     WORD32 blk_sz;
89     WORD32 vrnc;
90     WORD32 i;
91     WORD32 j;
92     UNUSED(wd);
93     UNUSED(ht);
94 
95     ASSERT(wd == 8);
96     ASSERT(ht == 4);
97 
98     sum     = 0;
99     sum_sqr = 0;
100 
101     blk_sz = 8 * 4;
102 
103     /*************************************************************************/
104     /* variance                                                              */
105     /* var = (n * SUM(x_i^2) - (SUM(x_i))^2) / (n^2);                        */
106     /*************************************************************************/
107 
108     /*************************************************************************/
109     /* The outer-loop runs for BLK_HT/2 times, because it                    */
110     /* calculates the variance only for field area not frame one.            */
111     /*************************************************************************/
112     for(j = 0; j < 4; j ++)
113     {
114         for(i = 0; i < 8; i++)
115         {
116             sum_sqr += (*pu1_src) * (*pu1_src);
117             sum     +=  *pu1_src++;
118         }
119         pu1_src += (src_strd - 8);
120     }
121 
122     vrnc = ((sum_sqr * blk_sz) - (sum * sum)) / (blk_sz * blk_sz);
123 
124     return vrnc;
125 }
126 
127