image_webp/
transform.rs

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}
image_webp/transform.rs

image_webp/
transform.rs
