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Auto merge of #3694 - southball:fix/use_strict_ops_instead_of_checked_ops, r=RalfJung

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Use strict ops instead of checked ops

## What

Replace `checked_add(...).unwrap()` with `strict_add(...)`, etc.

Resolves #3668.
This commit is contained in:
bors 2024-06-21 09:19:59 +00:00
commit be307ca809
14 changed files with 65 additions and 75 deletions
Download patch file Download diff file Expand all files Collapse all files

2
src/tools/miri/src/alloc_addresses/mod.rs
View file

@ -97,7 +97,7 @@ impl GlobalStateInner {
fn align_addr(addr: u64, align: u64) -> u64 {
match addr % align {
0 => addr,
rem => addr.checked_add(align).unwrap() - rem,
rem => addr.strict_add(align) - rem,
}
}

2
src/tools/miri/src/eval.rs
View file

@ -303,7 +303,7 @@ pub fn create_ecx<'tcx>(
let mut argvs = Vec::<Immediate<Provenance>>::with_capacity(config.args.len());
for arg in config.args.iter() {
// Make space for `0` terminator.
let size = u64::try_from(arg.len()).unwrap().checked_add(1).unwrap();
let size = u64::try_from(arg.len()).unwrap().strict_add(1);
let arg_type = Ty::new_array(tcx, tcx.types.u8, size);
let arg_place =
ecx.allocate(ecx.layout_of(arg_type)?, MiriMemoryKind::Machine.into())?;

6
src/tools/miri/src/helpers.rs
View file

@ -973,7 +973,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
// If `size` is smaller or equal than `bytes.len()`, writing `bytes` plus the required null
// terminator to memory using the `ptr` pointer would cause an out-of-bounds access.
let string_length = u64::try_from(c_str.len()).unwrap();
let string_length = string_length.checked_add(1).unwrap();
let string_length = string_length.strict_add(1);
if size < string_length {
return Ok((false, string_length));
}
@ -1037,7 +1037,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
// If `size` is smaller or equal than `bytes.len()`, writing `bytes` plus the required
// 0x0000 terminator to memory would cause an out-of-bounds access.
let string_length = u64::try_from(wide_str.len()).unwrap();
let string_length = string_length.checked_add(1).unwrap();
let string_length = string_length.strict_add(1);
if size < string_length {
return Ok((false, string_length));
}
@ -1406,7 +1406,7 @@ pub(crate) fn windows_check_buffer_size((success, len): (bool, u64)) -> u32 {
if success {
// If the function succeeds, the return value is the number of characters stored in the target buffer,
// not including the terminating null character.
u32::try_from(len.checked_sub(1).unwrap()).unwrap()
u32::try_from(len.strict_sub(1)).unwrap()
} else {
// If the target buffer was not large enough to hold the data, the return value is the buffer size, in characters,
// required to hold the string and its terminating null character.

4
src/tools/miri/src/shims/foreign_items.rs
View file

@ -402,7 +402,7 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
});
let (_, addr) = ptr.into_parts(); // we know the offset is absolute
// Cannot panic since `align` is a power of 2 and hence non-zero.
if addr.bytes().checked_rem(align.bytes()).unwrap() != 0 {
if addr.bytes().strict_rem(align.bytes()) != 0 {
throw_unsup_format!(
"`miri_promise_symbolic_alignment`: pointer is not actually aligned"
);
@ -714,7 +714,7 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
// That is probably overly cautious, but there also is no fundamental
// reason to have `strcpy` destroy pointer provenance.
// This reads at least 1 byte, so we are already enforcing that this is a valid pointer.
let n = this.read_c_str(ptr_src)?.len().checked_add(1).unwrap();
let n = this.read_c_str(ptr_src)?.len().strict_add(1);
this.mem_copy(ptr_src, ptr_dest, Size::from_bytes(n), true)?;
this.write_pointer(ptr_dest, dest)?;
}

2
src/tools/miri/src/shims/time.rs
View file

@ -165,7 +165,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
("tm_hour", dt.hour().into()),
("tm_mday", dt.day().into()),
("tm_mon", dt.month0().into()),
("tm_year", dt.year().checked_sub(1900).unwrap().into()),
("tm_year", dt.year().strict_sub(1900).into()),
("tm_wday", dt.weekday().num_days_from_sunday().into()),
("tm_yday", dt.ordinal0().into()),
("tm_isdst", tm_isdst),

6
src/tools/miri/src/shims/unix/env.rs
View file

@ -81,10 +81,8 @@ impl<'tcx> UnixEnvVars<'tcx> {
return Ok(None);
};
// The offset is used to strip the "{name}=" part of the string.
let var_ptr = var_ptr.offset(
Size::from_bytes(u64::try_from(name.len()).unwrap().checked_add(1).unwrap()),
ecx,
)?;
let var_ptr = var_ptr
.offset(Size::from_bytes(u64::try_from(name.len()).unwrap().strict_add(1)), ecx)?;
Ok(Some(var_ptr))
}

2
src/tools/miri/src/shims/unix/fd.rs
View file

@ -240,7 +240,7 @@ impl FdTable {
let new_fd = candidate_new_fd.unwrap_or_else(|| {
// find_map ran out of BTreeMap entries before finding a free fd, use one plus the
// maximum fd in the map
self.fds.last_key_value().map(|(fd, _)| fd.checked_add(1).unwrap()).unwrap_or(min_fd)
self.fds.last_key_value().map(|(fd, _)| fd.strict_add(1)).unwrap_or(min_fd)
});
self.fds.try_insert(new_fd, file_handle).unwrap();

2
src/tools/miri/src/shims/unix/socket.rs
View file

@ -116,7 +116,7 @@ impl FileDescription for SocketPair {
};
let mut writebuf = writebuf.borrow_mut();
let data_size = writebuf.buf.len();
let available_space = MAX_SOCKETPAIR_BUFFER_CAPACITY.checked_sub(data_size).unwrap();
let available_space = MAX_SOCKETPAIR_BUFFER_CAPACITY.strict_sub(data_size);
if available_space == 0 {
if self.is_nonblock {
// Non-blocking socketpair with a full buffer.

4
src/tools/miri/src/shims/windows/foreign_items.rs
View file

@ -647,7 +647,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
// If the function succeeds, the return value is the length of the string that
// is copied to the buffer, in characters, not including the terminating null
// character.
this.write_int(size_needed.checked_sub(1).unwrap(), dest)?;
this.write_int(size_needed.strict_sub(1), dest)?;
} else {
// If the buffer is too small to hold the module name, the string is truncated
// to nSize characters including the terminating null character, the function
@ -689,7 +689,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
throw_unsup_format!("FormatMessageW: buffer not big enough");
}
// The return value is the number of characters stored *excluding* the null terminator.
this.write_int(length.checked_sub(1).unwrap(), dest)?;
this.write_int(length.strict_sub(1), dest)?;
}
// Incomplete shims that we "stub out" just to get pre-main initialization code to work.

4
src/tools/miri/src/shims/windows/handle.rs
View file

@ -74,7 +74,7 @@ impl Handle {
/// None of this layout is guaranteed to applications by Windows or Miri.
fn to_packed(self) -> u32 {
let disc_size = Self::packed_disc_size();
let data_size = u32::BITS.checked_sub(disc_size).unwrap();
let data_size = u32::BITS.strict_sub(disc_size);
let discriminant = self.discriminant();
let data = self.data();
@ -103,7 +103,7 @@ impl Handle {
/// see docs for `to_packed`
fn from_packed(handle: u32) -> Option<Self> {
let disc_size = Self::packed_disc_size();
let data_size = u32::BITS.checked_sub(disc_size).unwrap();
let data_size = u32::BITS.strict_sub(disc_size);
// the lower `data_size` bits of this mask are 1
#[allow(clippy::arithmetic_side_effects)] // cannot overflow

35
src/tools/miri/src/shims/x86/avx2.rs
View file

@ -75,7 +75,7 @@ pub(super) trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
assert_eq!(dest_len, mask_len);
let mask_item_size = mask.layout.field(this, 0).size;
let high_bit_offset = mask_item_size.bits().checked_sub(1).unwrap();
let high_bit_offset = mask_item_size.bits().strict_sub(1);
let scale = this.read_scalar(scale)?.to_i8()?;
if !matches!(scale, 1 | 2 | 4 | 8) {
@ -93,8 +93,7 @@ pub(super) trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
let offset =
i64::try_from(this.read_scalar(&offset)?.to_int(offset.layout.size)?)
.unwrap();
let ptr = slice
.wrapping_signed_offset(offset.checked_mul(scale).unwrap(), &this.tcx);
let ptr = slice.wrapping_signed_offset(offset.strict_mul(scale), &this.tcx);
// Unaligned copy, which is what we want.
this.mem_copy(
ptr,
@ -124,22 +123,22 @@ pub(super) trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
let (dest, dest_len) = this.mplace_to_simd(dest)?;
assert_eq!(left_len, right_len);
assert_eq!(dest_len.checked_mul(2).unwrap(), left_len);
assert_eq!(dest_len.strict_mul(2), left_len);
for i in 0..dest_len {
let j1 = i.checked_mul(2).unwrap();
let j1 = i.strict_mul(2);
let left1 = this.read_scalar(&this.project_index(&left, j1)?)?.to_i16()?;
let right1 = this.read_scalar(&this.project_index(&right, j1)?)?.to_i16()?;
let j2 = j1.checked_add(1).unwrap();
let j2 = j1.strict_add(1);
let left2 = this.read_scalar(&this.project_index(&left, j2)?)?.to_i16()?;
let right2 = this.read_scalar(&this.project_index(&right, j2)?)?.to_i16()?;
let dest = this.project_index(&dest, i)?;
// Multiplications are i16*i16->i32, which will not overflow.
let mul1 = i32::from(left1).checked_mul(right1.into()).unwrap();
let mul2 = i32::from(left2).checked_mul(right2.into()).unwrap();
let mul1 = i32::from(left1).strict_mul(right1.into());
let mul2 = i32::from(left2).strict_mul(right2.into());
// However, this addition can overflow in the most extreme case
// (-0x8000)*(-0x8000)+(-0x8000)*(-0x8000) = 0x80000000
let res = mul1.wrapping_add(mul2);
@ -161,22 +160,22 @@ pub(super) trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
let (dest, dest_len) = this.mplace_to_simd(dest)?;
assert_eq!(left_len, right_len);
assert_eq!(dest_len.checked_mul(2).unwrap(), left_len);
assert_eq!(dest_len.strict_mul(2), left_len);
for i in 0..dest_len {
let j1 = i.checked_mul(2).unwrap();
let j1 = i.strict_mul(2);
let left1 = this.read_scalar(&this.project_index(&left, j1)?)?.to_u8()?;
let right1 = this.read_scalar(&this.project_index(&right, j1)?)?.to_i8()?;
let j2 = j1.checked_add(1).unwrap();
let j2 = j1.strict_add(1);
let left2 = this.read_scalar(&this.project_index(&left, j2)?)?.to_u8()?;
let right2 = this.read_scalar(&this.project_index(&right, j2)?)?.to_i8()?;
let dest = this.project_index(&dest, i)?;
// Multiplication of a u8 and an i8 into an i16 cannot overflow.
let mul1 = i16::from(left1).checked_mul(right1.into()).unwrap();
let mul2 = i16::from(left2).checked_mul(right2.into()).unwrap();
let mul1 = i16::from(left1).strict_mul(right1.into());
let mul2 = i16::from(left2).strict_mul(right2.into());
let res = mul1.saturating_add(mul2);
this.write_scalar(Scalar::from_i16(res), &dest)?;
@ -309,7 +308,7 @@ pub(super) trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
for i in 0..2 {
let dest = this.project_index(&dest, i)?;
let src = match (imm >> i.checked_mul(4).unwrap()) & 0b11 {
let src = match (imm >> i.strict_mul(4)) & 0b11 {
0 => this.project_index(&left, 0)?,
1 => this.project_index(&left, 1)?,
2 => this.project_index(&right, 0)?,
@ -336,14 +335,14 @@ pub(super) trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
let (dest, dest_len) = this.mplace_to_simd(dest)?;
assert_eq!(left_len, right_len);
assert_eq!(left_len, dest_len.checked_mul(8).unwrap());
assert_eq!(left_len, dest_len.strict_mul(8));
for i in 0..dest_len {
let dest = this.project_index(&dest, i)?;
let mut acc: u16 = 0;
for j in 0..8 {
let src_index = i.checked_mul(8).unwrap().checked_add(j).unwrap();
let src_index = i.strict_mul(8).strict_add(j);
let left = this.project_index(&left, src_index)?;
let left = this.read_scalar(&left)?.to_u8()?;
@ -351,7 +350,7 @@ pub(super) trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
let right = this.project_index(&right, src_index)?;
let right = this.read_scalar(&right)?.to_u8()?;
acc = acc.checked_add(left.abs_diff(right).into()).unwrap();
acc = acc.strict_add(left.abs_diff(right).into());
}
this.write_scalar(Scalar::from_u64(acc.into()), &dest)?;
@ -377,7 +376,7 @@ pub(super) trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
let res = if right & 0x80 == 0 {
// Shuffle each 128-bit (16-byte) block independently.
let j = u64::from(right % 16).checked_add(i & !15).unwrap();
let j = u64::from(right % 16).strict_add(i & !15);
this.read_scalar(&this.project_index(&left, j)?)?
} else {
// If the highest bit in `right` is 1, write zero.

45
src/tools/miri/src/shims/x86/mod.rs
View file

@ -441,8 +441,7 @@ fn apply_random_float_error<F: rustc_apfloat::Float>(
) -> F {
let rng = this.machine.rng.get_mut();
// generates rand(0, 2^64) * 2^(scale - 64) = rand(0, 1) * 2^scale
let err =
F::from_u128(rng.gen::<u64>().into()).value.scalbn(err_scale.checked_sub(64).unwrap());
let err = F::from_u128(rng.gen::<u64>().into()).value.scalbn(err_scale.strict_sub(64));
// give it a random sign
let err = if rng.gen::<bool>() { -err } else { err };
// multiple the value with (1+err)
@ -793,7 +792,7 @@ fn split_simd_to_128bit_chunks<'tcx, P: Projectable<'tcx, Provenance>>(
assert_eq!(simd_layout.size.bits() % 128, 0);
let num_chunks = simd_layout.size.bits() / 128;
let items_per_chunk = simd_len.checked_div(num_chunks).unwrap();
let items_per_chunk = simd_len.strict_div(num_chunks);
// Transmute to `[[T; items_per_chunk]; num_chunks]`
let chunked_layout = this
@ -841,13 +840,11 @@ fn horizontal_bin_op<'tcx>(
for j in 0..items_per_chunk {
// `j` is the index in `dest`
// `k` is the index of the 2-item chunk in `src`
let (k, src) =
if j < middle { (j, &left) } else { (j.checked_sub(middle).unwrap(), &right) };
let (k, src) = if j < middle { (j, &left) } else { (j.strict_sub(middle), &right) };
// `base_i` is the index of the first item of the 2-item chunk in `src`
let base_i = k.checked_mul(2).unwrap();
let base_i = k.strict_mul(2);
let lhs = this.read_immediate(&this.project_index(src, base_i)?)?;
let rhs =
this.read_immediate(&this.project_index(src, base_i.checked_add(1).unwrap())?)?;
let rhs = this.read_immediate(&this.project_index(src, base_i.strict_add(1))?)?;
let res = if saturating {
Immediate::from(this.saturating_arith(which, &lhs, &rhs)?)
@ -900,7 +897,7 @@ fn conditional_dot_product<'tcx>(
// for the initial value because the representation of 0.0 is all zero bits.
let mut sum = ImmTy::from_int(0u8, element_layout);
for j in 0..items_per_chunk {
if imm & (1 << j.checked_add(4).unwrap()) != 0 {
if imm & (1 << j.strict_add(4)) != 0 {
let left = this.read_immediate(&this.project_index(&left, j)?)?;
let right = this.read_immediate(&this.project_index(&right, j)?)?;
@ -971,7 +968,7 @@ fn test_high_bits_masked<'tcx>(
assert_eq!(op_len, mask_len);
let high_bit_offset = op.layout.field(this, 0).size.bits().checked_sub(1).unwrap();
let high_bit_offset = op.layout.field(this, 0).size.bits().strict_sub(1);
let mut direct = true;
let mut negated = true;
@ -1002,7 +999,7 @@ fn mask_load<'tcx>(
assert_eq!(dest_len, mask_len);
let mask_item_size = mask.layout.field(this, 0).size;
let high_bit_offset = mask_item_size.bits().checked_sub(1).unwrap();
let high_bit_offset = mask_item_size.bits().strict_sub(1);
let ptr = this.read_pointer(ptr)?;
for i in 0..dest_len {
@ -1035,7 +1032,7 @@ fn mask_store<'tcx>(
assert_eq!(value_len, mask_len);
let mask_item_size = mask.layout.field(this, 0).size;
let high_bit_offset = mask_item_size.bits().checked_sub(1).unwrap();
let high_bit_offset = mask_item_size.bits().strict_sub(1);
let ptr = this.read_pointer(ptr)?;
for i in 0..value_len {
@ -1077,15 +1074,15 @@ fn mpsadbw<'tcx>(
let (_, _, right) = split_simd_to_128bit_chunks(this, right)?;
let (_, dest_items_per_chunk, dest) = split_simd_to_128bit_chunks(this, dest)?;
assert_eq!(op_items_per_chunk, dest_items_per_chunk.checked_mul(2).unwrap());
assert_eq!(op_items_per_chunk, dest_items_per_chunk.strict_mul(2));
let imm = this.read_scalar(imm)?.to_uint(imm.layout.size)?;
// Bit 2 of `imm` specifies the offset for indices of `left`.
// The offset is 0 when the bit is 0 or 4 when the bit is 1.
let left_offset = u64::try_from((imm >> 2) & 1).unwrap().checked_mul(4).unwrap();
let left_offset = u64::try_from((imm >> 2) & 1).unwrap().strict_mul(4);
// Bits 0..=1 of `imm` specify the offset for indices of
// `right` in blocks of 4 elements.
let right_offset = u64::try_from(imm & 0b11).unwrap().checked_mul(4).unwrap();
let right_offset = u64::try_from(imm & 0b11).unwrap().strict_mul(4);
for i in 0..num_chunks {
let left = this.project_index(&left, i)?;
@ -1093,18 +1090,16 @@ fn mpsadbw<'tcx>(
let dest = this.project_index(&dest, i)?;
for j in 0..dest_items_per_chunk {
let left_offset = left_offset.checked_add(j).unwrap();
let left_offset = left_offset.strict_add(j);
let mut res: u16 = 0;
for k in 0..4 {
let left = this
.read_scalar(&this.project_index(&left, left_offset.checked_add(k).unwrap())?)?
.read_scalar(&this.project_index(&left, left_offset.strict_add(k))?)?
.to_u8()?;
let right = this
.read_scalar(
&this.project_index(&right, right_offset.checked_add(k).unwrap())?,
)?
.read_scalar(&this.project_index(&right, right_offset.strict_add(k))?)?
.to_u8()?;
res = res.checked_add(left.abs_diff(right).into()).unwrap();
res = res.strict_add(left.abs_diff(right).into());
}
this.write_scalar(Scalar::from_u16(res), &this.project_index(&dest, j)?)?;
}
@ -1138,8 +1133,7 @@ fn pmulhrsw<'tcx>(
let right = this.read_scalar(&this.project_index(&right, i)?)?.to_i16()?;
let dest = this.project_index(&dest, i)?;
let res =
(i32::from(left).checked_mul(right.into()).unwrap() >> 14).checked_add(1).unwrap() >> 1;
let res = (i32::from(left).strict_mul(right.into()) >> 14).strict_add(1) >> 1;
// The result of this operation can overflow a signed 16-bit integer.
// When `left` and `right` are -0x8000, the result is 0x8000.
@ -1235,7 +1229,7 @@ fn pack_generic<'tcx>(
let (_, _, right) = split_simd_to_128bit_chunks(this, right)?;
let (_, dest_items_per_chunk, dest) = split_simd_to_128bit_chunks(this, dest)?;
assert_eq!(dest_items_per_chunk, op_items_per_chunk.checked_mul(2).unwrap());
assert_eq!(dest_items_per_chunk, op_items_per_chunk.strict_mul(2));
for i in 0..num_chunks {
let left = this.project_index(&left, i)?;
@ -1246,8 +1240,7 @@ fn pack_generic<'tcx>(
let left = this.read_scalar(&this.project_index(&left, j)?)?;
let right = this.read_scalar(&this.project_index(&right, j)?)?;
let left_dest = this.project_index(&dest, j)?;
let right_dest =
this.project_index(&dest, j.checked_add(op_items_per_chunk).unwrap())?;
let right_dest = this.project_index(&dest, j.strict_add(op_items_per_chunk))?;
let left_res = f(left)?;
let right_res = f(right)?;

16
src/tools/miri/src/shims/x86/sse2.rs
View file

@ -47,22 +47,22 @@ pub(super) trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
let (dest, dest_len) = this.mplace_to_simd(dest)?;
assert_eq!(left_len, right_len);
assert_eq!(dest_len.checked_mul(2).unwrap(), left_len);
assert_eq!(dest_len.strict_mul(2), left_len);
for i in 0..dest_len {
let j1 = i.checked_mul(2).unwrap();
let j1 = i.strict_mul(2);
let left1 = this.read_scalar(&this.project_index(&left, j1)?)?.to_i16()?;
let right1 = this.read_scalar(&this.project_index(&right, j1)?)?.to_i16()?;
let j2 = j1.checked_add(1).unwrap();
let j2 = j1.strict_add(1);
let left2 = this.read_scalar(&this.project_index(&left, j2)?)?.to_i16()?;
let right2 = this.read_scalar(&this.project_index(&right, j2)?)?.to_i16()?;
let dest = this.project_index(&dest, i)?;
// Multiplications are i16*i16->i32, which will not overflow.
let mul1 = i32::from(left1).checked_mul(right1.into()).unwrap();
let mul2 = i32::from(left2).checked_mul(right2.into()).unwrap();
let mul1 = i32::from(left1).strict_mul(right1.into());
let mul2 = i32::from(left2).strict_mul(right2.into());
// However, this addition can overflow in the most extreme case
// (-0x8000)*(-0x8000)+(-0x8000)*(-0x8000) = 0x80000000
let res = mul1.wrapping_add(mul2);
@ -94,14 +94,14 @@ pub(super) trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
let dest = this.project_index(&dest, i)?;
let mut res: u16 = 0;
let n = left_len.checked_div(dest_len).unwrap();
let n = left_len.strict_div(dest_len);
for j in 0..n {
let op_i = j.checked_add(i.checked_mul(n).unwrap()).unwrap();
let op_i = j.strict_add(i.strict_mul(n));
let left = this.read_scalar(&this.project_index(&left, op_i)?)?.to_u8()?;
let right =
this.read_scalar(&this.project_index(&right, op_i)?)?.to_u8()?;
res = res.checked_add(left.abs_diff(right).into()).unwrap();
res = res.strict_add(left.abs_diff(right).into());
}
this.write_scalar(Scalar::from_u64(res.into()), &dest)?;

10
src/tools/miri/src/shims/x86/ssse3.rs
View file

@ -89,22 +89,22 @@ pub(super) trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
let (dest, dest_len) = this.mplace_to_simd(dest)?;
assert_eq!(left_len, right_len);
assert_eq!(dest_len.checked_mul(2).unwrap(), left_len);
assert_eq!(dest_len.strict_mul(2), left_len);
for i in 0..dest_len {
let j1 = i.checked_mul(2).unwrap();
let j1 = i.strict_mul(2);
let left1 = this.read_scalar(&this.project_index(&left, j1)?)?.to_u8()?;
let right1 = this.read_scalar(&this.project_index(&right, j1)?)?.to_i8()?;
let j2 = j1.checked_add(1).unwrap();
let j2 = j1.strict_add(1);
let left2 = this.read_scalar(&this.project_index(&left, j2)?)?.to_u8()?;
let right2 = this.read_scalar(&this.project_index(&right, j2)?)?.to_i8()?;
let dest = this.project_index(&dest, i)?;
// Multiplication of a u8 and an i8 into an i16 cannot overflow.
let mul1 = i16::from(left1).checked_mul(right1.into()).unwrap();
let mul2 = i16::from(left2).checked_mul(right2.into()).unwrap();
let mul1 = i16::from(left1).strict_mul(right1.into());
let mul2 = i16::from(left2).strict_mul(right2.into());
let res = mul1.saturating_add(mul2);
this.write_scalar(Scalar::from_i16(res), &dest)?;