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    static CONST1: i64 = 20091;
    static CONST2: i64 = 35468;

    pub fn idct4x4(block: &mut [i32]) {
        // The intermediate results may overflow the types, so we stretch the type.
        fn fetch(block: &mut [i32], idx: usize) -> i64 {
            i64::from(block[idx])
        }

        for i in 0usize..4 {
            let a1 = fetch(block, i) + fetch(block, 8 + i);
            let b1 = fetch(block, i) - fetch(block, 8 + i);

            let t1 = (fetch(block, 4 + i) * CONST2) >> 16;
            let t2 = fetch(block, 12 + i) + ((fetch(block, 12 + i) * CONST1) >> 16);
            let c1 = t1 - t2;

            let t1 = fetch(block, 4 + i) + ((fetch(block, 4 + i) * CONST1) >> 16);
            let t2 = (fetch(block, 12 + i) * CONST2) >> 16;
            let d1 = t1 + t2;

            block[i] = (a1 + d1) as i32;
            block[4 + i] = (b1 + c1) as i32;
            block[4 * 3 + i] = (a1 - d1) as i32;
            block[4 * 2 + i] = (b1 - c1) as i32;
        }

        for i in 0usize..4 {
            let a1 = fetch(block, 4 * i) + fetch(block, 4 * i + 2);
            let b1 = fetch(block, 4 * i) - fetch(block, 4 * i + 2);

            let t1 = (fetch(block, 4 * i + 1) * CONST2) >> 16;
            let t2 = fetch(block, 4 * i + 3) + ((fetch(block, 4 * i + 3) * CONST1) >> 16);
            let c1 = t1 - t2;

            let t1 = fetch(block, 4 * i + 1) + ((fetch(block, 4 * i + 1) * CONST1) >> 16);
            let t2 = (fetch(block, 4 * i + 3) * CONST2) >> 16;
            let d1 = t1 + t2;

            block[4 * i] = ((a1 + d1 + 4) >> 3) as i32;
            block[4 * i + 3] = ((a1 - d1 + 4) >> 3) as i32;
            block[4 * i + 1] = ((b1 + c1 + 4) >> 3) as i32;
            block[4 * i + 2] = ((b1 - c1 + 4) >> 3) as i32;
        }
    }

    // 14.3
    pub fn iwht4x4(block: &mut [i32]) {
        for i in 0usize..4 {
            let a1 = block[i] + block[12 + i];
            let b1 = block[4 + i] + block[8 + i];
            let c1 = block[4 + i] - block[8 + i];
            let d1 = block[i] - block[12 + i];

            block[i] = a1 + b1;
            block[4 + i] = c1 + d1;
            block[8 + i] = a1 - b1;
            block[12 + i] = d1 - c1;
        }

        for i in 0usize..4 {
            let a1 = block[4 * i] + block[4 * i + 3];
            let b1 = block[4 * i + 1] + block[4 * i + 2];
            let c1 = block[4 * i + 1] - block[4 * i + 2];
            let d1 = block[4 * i] - block[4 * i + 3];

            let a2 = a1 + b1;
            let b2 = c1 + d1;
            let c2 = a1 - b1;
            let d2 = d1 - c1;

            block[4 * i] = (a2 + 3) >> 3;
            block[4 * i + 1] = (b2 + 3) >> 3;
            block[4 * i + 2] = (c2 + 3) >> 3;
            block[4 * i + 3] = (d2 + 3) >> 3;
        }
    }

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