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Avoid bounds checks in IDCD and IWHT #9

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merged 2 commits into from
Oct 22, 2023
Merged

Avoid bounds checks in IDCD and IWHT #9

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bd03888
Avoid bounds checks in IDCD and IWHT
Shnatsel Oct 3, 2023
77f5d43
fix typo
Shnatsel Oct 21, 2023
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6 changes: 6 additions & 0 deletions src/transform.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,9 @@ pub(crate) fn idct4x4(block: &mut [i32]) {
i64::from(block[idx])
}

// Perform one lenght check up front to avoid subsequent bounds checks in this function
assert!(block.len() >= 16);

for i in 0usize..4 {
let a1 = fetch(block, i) + fetch(block, 8 + i);
let b1 = fetch(block, i) - fetch(block, 8 + i);
Expand Down Expand Up @@ -46,6 +49,9 @@ pub(crate) fn idct4x4(block: &mut [i32]) {

// 14.3
pub(crate) fn iwht4x4(block: &mut [i32]) {
// Perform one length check up front to avoid subsequent bounds checks in this function
assert!(block.len() >= 16);

for i in 0usize..4 {
let a1 = block[i] + block[12 + i];
let b1 = block[4 + i] + block[8 + i];
Expand Down