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Prevent unnecessary bounds check in SCB::{get_priority, set_priority} #202

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merged 3 commits into from
Mar 18, 2020
Merged

Prevent unnecessary bounds check in SCB::{get_priority, set_priority} #202

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536575c
Prevent unnecessary bounds check in SCB::{get_priority, set_priority}
qwerty19106 Mar 17, 2020
c3dba12
Update unsafe comments
qwerty19106 Mar 17, 2020
9c57405
Add TODO with link to rust-lang/rust/issues/13926
qwerty19106 Mar 18, 2020
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26 changes: 22 additions & 4 deletions src/peripheral/scb.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -949,13 +949,23 @@ impl SCB {
#[cfg(not(armv6m))]
{
// NOTE(unsafe) atomic read with no side effects
unsafe { (*Self::ptr()).shpr[usize::from(index - 4)].read() }

// NOTE(unsafe): Index is bounded to [4,15] by SystemHandler design.
// TODO: Review it after rust-lang/rust/issues/13926 will be fixed.
let priority_ref = unsafe {(*Self::ptr()).shpr.get_unchecked(usize::from(index - 4))};

priority_ref.read()
}

#[cfg(armv6m)]
{
// NOTE(unsafe) atomic read with no side effects
let shpr = unsafe { (*Self::ptr()).shpr[usize::from((index - 8) / 4)].read() };

// NOTE(unsafe): Index is bounded to [11,15] by SystemHandler design.
// TODO: Review it after rust-lang/rust/issues/13926 will be fixed.
let priority_ref = unsafe {(*Self::ptr()).shpr.get_unchecked(usize::from((index - 8) / 4))};

let shpr = priority_ref.read();
let prio = (shpr >> (8 * (index % 4))) & 0x0000_00ff;
prio as u8
}
Expand All @@ -979,12 +989,20 @@ impl SCB {

#[cfg(not(armv6m))]
{
self.shpr[usize::from(index - 4)].write(prio)
// NOTE(unsafe): Index is bounded to [4,15] by SystemHandler design.
// TODO: Review it after rust-lang/rust/issues/13926 will be fixed.
let priority_ref = (*Self::ptr()).shpr.get_unchecked(usize::from(index - 4));

priority_ref.write(prio)
}

#[cfg(armv6m)]
{
self.shpr[usize::from((index - 8) / 4)].modify(|value| {
// NOTE(unsafe): Index is bounded to [11,15] by SystemHandler design.
// TODO: Review it after rust-lang/rust/issues/13926 will be fixed.
let priority_ref = (*Self::ptr()).shpr.get_unchecked(usize::from((index - 8) / 4));

priority_ref.modify(|value| {
let shift = 8 * (index % 4);
let mask = 0x0000_00ff << shift;
let prio = u32::from(prio) << shift;
Expand Down