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Replace indexing with get_unchecked calls #143277

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Replace indexing with get_unchecked calls #143277

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86 changes: 66 additions & 20 deletions library/core/src/fmt/num.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -69,7 +69,10 @@ unsafe trait GenericRadix: Sized {
let n = x % base; // Get the current place value.
x = x / base; // Deaccumulate the number.
curr -= 1;
buf[curr].write(Self::digit(n.to_u8())); // Store the digit in the buffer.
// SAFETY: `curr` is always between 0 and `buf`'s length.
unsafe {
buf.get_unchecked_mut(curr).write(Self::digit(n.to_u8()));
} // Store the digit in the buffer.
if x == zero {
// No more digits left to accumulate.
break;
Expand All @@ -81,7 +84,10 @@ unsafe trait GenericRadix: Sized {
let n = zero - (x % base); // Get the current place value.
x = x / base; // Deaccumulate the number.
curr -= 1;
buf[curr].write(Self::digit(n.to_u8())); // Store the digit in the buffer.
// SAFETY: `curr` is always between 0 and `buf`'s length.
unsafe {
buf.get_unchecked_mut(curr).write(Self::digit(n.to_u8()));
} // Store the digit in the buffer.
if x == zero {
// No more digits left to accumulate.
break;
Expand Down Expand Up @@ -270,10 +276,14 @@ macro_rules! impl_Display {
remain /= scale;
let pair1 = (quad / 100) as usize;
let pair2 = (quad % 100) as usize;
buf[offset + 0].write(DEC_DIGITS_LUT[pair1 * 2 + 0]);
buf[offset + 1].write(DEC_DIGITS_LUT[pair1 * 2 + 1]);
buf[offset + 2].write(DEC_DIGITS_LUT[pair2 * 2 + 0]);
buf[offset + 3].write(DEC_DIGITS_LUT[pair2 * 2 + 1]);
// SAFETY: `offset` is always between 0 and `buf`'s length.
unsafe { buf.get_unchecked_mut(offset + 0).write(DEC_DIGITS_LUT[pair1 * 2 + 0]); }
// SAFETY: `offset` is always between 0 and `buf`'s length.
unsafe { buf.get_unchecked_mut(offset + 1).write(DEC_DIGITS_LUT[pair1 * 2 + 1]); }
// SAFETY: `offset` is always between 0 and `buf`'s length.
unsafe { buf.get_unchecked_mut(offset + 2).write(DEC_DIGITS_LUT[pair2 * 2 + 0]); }
// SAFETY: `offset` is always between 0 and `buf`'s length.
unsafe { buf.get_unchecked_mut(offset + 3).write(DEC_DIGITS_LUT[pair2 * 2 + 1]); }
}

// Format per two digits from the lookup table.
Expand All @@ -288,8 +298,10 @@ macro_rules! impl_Display {

let pair = (remain % 100) as usize;
remain /= 100;
buf[offset + 0].write(DEC_DIGITS_LUT[pair * 2 + 0]);
buf[offset + 1].write(DEC_DIGITS_LUT[pair * 2 + 1]);
// SAFETY: `offset` is always between 0 and `buf`'s length.
unsafe { buf.get_unchecked_mut(offset + 0).write(DEC_DIGITS_LUT[pair * 2 + 0]); }
// SAFETY: `offset` is always between 0 and `buf`'s length.
unsafe { buf.get_unchecked_mut(offset + 1).write(DEC_DIGITS_LUT[pair * 2 + 1]); }
}

// Format the last remaining digit, if any.
Expand All @@ -305,7 +317,8 @@ macro_rules! impl_Display {
// Either the compiler sees that remain < 10, or it prevents
// a boundary check up next.
let last = (remain & 15) as usize;
buf[offset].write(DEC_DIGITS_LUT[last * 2 + 1]);
// SAFETY: `offset` is always between 0 and `buf`'s length.
unsafe { buf.get_unchecked_mut(offset).write(DEC_DIGITS_LUT[last * 2 + 1]); }
// not used: remain = 0;
}

Expand Down Expand Up @@ -639,10 +652,22 @@ impl u128 {
remain /= 1_00_00;
let pair1 = (quad / 100) as usize;
let pair2 = (quad % 100) as usize;
buf[offset + 0].write(DEC_DIGITS_LUT[pair1 * 2 + 0]);
buf[offset + 1].write(DEC_DIGITS_LUT[pair1 * 2 + 1]);
buf[offset + 2].write(DEC_DIGITS_LUT[pair2 * 2 + 0]);
buf[offset + 3].write(DEC_DIGITS_LUT[pair2 * 2 + 1]);
// SAFETY: `offset` is always between 0 and `buf`'s length.
unsafe {
buf.get_unchecked_mut(offset + 0).write(DEC_DIGITS_LUT[pair1 * 2 + 0]);
}
// SAFETY: `offset` is always between 0 and `buf`'s length.
unsafe {
buf.get_unchecked_mut(offset + 1).write(DEC_DIGITS_LUT[pair1 * 2 + 1]);
}
// SAFETY: `offset` is always between 0 and `buf`'s length.
unsafe {
buf.get_unchecked_mut(offset + 2).write(DEC_DIGITS_LUT[pair2 * 2 + 0]);
}
// SAFETY: `offset` is always between 0 and `buf`'s length.
unsafe {
buf.get_unchecked_mut(offset + 3).write(DEC_DIGITS_LUT[pair2 * 2 + 1]);
}
}

// Format per two digits from the lookup table.
Expand All @@ -657,8 +682,14 @@ impl u128 {

let pair = (remain % 100) as usize;
remain /= 100;
buf[offset + 0].write(DEC_DIGITS_LUT[pair * 2 + 0]);
buf[offset + 1].write(DEC_DIGITS_LUT[pair * 2 + 1]);
// SAFETY: `offset` is always between 0 and `buf`'s length.
unsafe {
buf.get_unchecked_mut(offset + 0).write(DEC_DIGITS_LUT[pair * 2 + 0]);
}
// SAFETY: `offset` is always between 0 and `buf`'s length.
unsafe {
buf.get_unchecked_mut(offset + 1).write(DEC_DIGITS_LUT[pair * 2 + 1]);
}
}

// Format the last remaining digit, if any.
Expand All @@ -674,7 +705,10 @@ impl u128 {
// Either the compiler sees that remain < 10, or it prevents
// a boundary check up next.
let last = (remain & 15) as usize;
buf[offset].write(DEC_DIGITS_LUT[last * 2 + 1]);
// SAFETY: `offset` is always between 0 and `buf`'s length.
unsafe {
buf.get_unchecked_mut(offset).write(DEC_DIGITS_LUT[last * 2 + 1]);
}
// not used: remain = 0;
}

Expand Down Expand Up @@ -703,10 +737,22 @@ fn enc_16lsd<const OFFSET: usize>(buf: &mut [MaybeUninit<u8>], n: u64) {
remain /= 1_00_00;
let pair1 = (quad / 100) as usize;
let pair2 = (quad % 100) as usize;
buf[quad_index * 4 + OFFSET + 0].write(DEC_DIGITS_LUT[pair1 * 2 + 0]);
buf[quad_index * 4 + OFFSET + 1].write(DEC_DIGITS_LUT[pair1 * 2 + 1]);
buf[quad_index * 4 + OFFSET + 2].write(DEC_DIGITS_LUT[pair2 * 2 + 0]);
buf[quad_index * 4 + OFFSET + 3].write(DEC_DIGITS_LUT[pair2 * 2 + 1]);
// SAFETY: `quad_index * 4 + OFFSET` is always between 0 and `buf`'s length.
unsafe {
buf.get_unchecked_mut(quad_index * 4 + OFFSET + 0).write(DEC_DIGITS_LUT[pair1 * 2 + 0]);
}
// SAFETY: `quad_index * 4 + OFFSET` is always between 0 and `buf`'s length.
unsafe {
buf.get_unchecked_mut(quad_index * 4 + OFFSET + 1).write(DEC_DIGITS_LUT[pair1 * 2 + 1]);
}
// SAFETY: `quad_index * 4 + OFFSET` is always between 0 and `buf`'s length.
unsafe {
buf.get_unchecked_mut(quad_index * 4 + OFFSET + 2).write(DEC_DIGITS_LUT[pair2 * 2 + 0]);
}
// SAFETY: `quad_index * 4 + OFFSET` is always between 0 and `buf`'s length.
unsafe {
buf.get_unchecked_mut(quad_index * 4 + OFFSET + 3).write(DEC_DIGITS_LUT[pair2 * 2 + 1]);
}
}
}

Expand Down
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