1static CONST1: i64 = 20091;
2static CONST2: i64 = 35468;
3
4pub(crate) fn idct4x4(block: &mut [i32]) {
5 // The intermediate results may overflow the types, so we stretch the type.
6 fn fetch(block: &[i32], idx: usize) -> i64 {
7 i64::from(block[idx])
8 }
9
10 // Perform one lenght check up front to avoid subsequent bounds checks in this function
11 assert!(block.len() >= 16);
12
13 for i in 0usize..4 {
14 let a1 = fetch(block, i) + fetch(block, 8 + i);
15 let b1 = fetch(block, i) - fetch(block, 8 + i);
16
17 let t1 = (fetch(block, 4 + i) * CONST2) >> 16;
18 let t2 = fetch(block, 12 + i) + ((fetch(block, 12 + i) * CONST1) >> 16);
19 let c1 = t1 - t2;
20
21 let t1 = fetch(block, 4 + i) + ((fetch(block, 4 + i) * CONST1) >> 16);
22 let t2 = (fetch(block, 12 + i) * CONST2) >> 16;
23 let d1 = t1 + t2;
24
25 block[i] = (a1 + d1) as i32;
26 block[4 + i] = (b1 + c1) as i32;
27 block[4 * 3 + i] = (a1 - d1) as i32;
28 block[4 * 2 + i] = (b1 - c1) as i32;
29 }
30
31 for i in 0usize..4 {
32 let a1 = fetch(block, 4 * i) + fetch(block, 4 * i + 2);
33 let b1 = fetch(block, 4 * i) - fetch(block, 4 * i + 2);
34
35 let t1 = (fetch(block, 4 * i + 1) * CONST2) >> 16;
36 let t2 = fetch(block, 4 * i + 3) + ((fetch(block, 4 * i + 3) * CONST1) >> 16);
37 let c1 = t1 - t2;
38
39 let t1 = fetch(block, 4 * i + 1) + ((fetch(block, 4 * i + 1) * CONST1) >> 16);
40 let t2 = (fetch(block, 4 * i + 3) * CONST2) >> 16;
41 let d1 = t1 + t2;
42
43 block[4 * i] = ((a1 + d1 + 4) >> 3) as i32;
44 block[4 * i + 3] = ((a1 - d1 + 4) >> 3) as i32;
45 block[4 * i + 1] = ((b1 + c1 + 4) >> 3) as i32;
46 block[4 * i + 2] = ((b1 - c1 + 4) >> 3) as i32;
47 }
48}
49
50// 14.3
51pub(crate) fn iwht4x4(block: &mut [i32]) {
52 // Perform one length check up front to avoid subsequent bounds checks in this function
53 assert!(block.len() >= 16);
54
55 for i in 0usize..4 {
56 let a1 = block[i] + block[12 + i];
57 let b1 = block[4 + i] + block[8 + i];
58 let c1 = block[4 + i] - block[8 + i];
59 let d1 = block[i] - block[12 + i];
60
61 block[i] = a1 + b1;
62 block[4 + i] = c1 + d1;
63 block[8 + i] = a1 - b1;
64 block[12 + i] = d1 - c1;
65 }
66
67 for block in block.chunks_exact_mut(4) {
68 let a1 = block[0] + block[3];
69 let b1 = block[1] + block[2];
70 let c1 = block[1] - block[2];
71 let d1 = block[0] - block[3];
72
73 let a2 = a1 + b1;
74 let b2 = c1 + d1;
75 let c2 = a1 - b1;
76 let d2 = d1 - c1;
77
78 block[0] = (a2 + 3) >> 3;
79 block[1] = (b2 + 3) >> 3;
80 block[2] = (c2 + 3) >> 3;
81 block[3] = (d2 + 3) >> 3;
82 }
83}
84