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cmov: use masksel to impl CmovEq #1343

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Merged
tarcieri merged 1 commit into from
Jan 15, 2026
+91 −98
Merged

cmov: use masksel to impl CmovEq #1343

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189 changes: 91 additions & 98 deletions cmov/src/portable.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -54,12 +54,12 @@ impl Cmov for u32 {
impl CmovEq for u32 {
#[inline]
fn cmovne(&self, rhs: &Self, input: Condition, output: &mut Condition) {
output.cmovnz(&input, testne32(*self, *rhs));
*output = masksel(*output, input, (maskne32(*self, *rhs) & 0xFF) as u8);
}

#[inline]
fn cmoveq(&self, rhs: &Self, input: Condition, output: &mut Condition) {
output.cmovnz(&input, testeq32(*self, *rhs));
*output = masksel(*output, input, (maskeq32(*self, *rhs) & 0xFF) as u8);
}
}

Expand All @@ -78,25 +78,49 @@ impl Cmov for u64 {
impl CmovEq for u64 {
#[inline]
fn cmovne(&self, rhs: &Self, input: Condition, output: &mut Condition) {
output.cmovnz(&input, testne64(*self, *rhs));
*output = masksel(*output, input, (maskne64(*self, *rhs) & 0xFF) as u8);
}

#[inline]
fn cmoveq(&self, rhs: &Self, input: Condition, output: &mut Condition) {
output.cmovnz(&input, testeq64(*self, *rhs));
*output = masksel(*output, input, (maskeq64(*self, *rhs) & 0xFF) as u8);
}
}

/// Returns `u32::MAX` if `x` is equal to `y`, otherwise returns `0` (32-bit version)
fn maskeq32(x: u32, y: u32) -> u32 {
!maskne32(x, y)
}

/// Returns `u32::MAX` if `x` is equal to `y`, otherwise returns `0` (64-bit version)
fn maskeq64(x: u64, y: u64) -> u64 {
!maskne64(x, y)
}

/// Returns `0` if `x` is equal to `y`, otherwise returns `1` (32-bit version)
fn maskne32(x: u32, y: u32) -> u32 {
masknz32(x ^ y)
}

/// Returns `0` if `x` is equal to `y`, otherwise returns `1` (64-bit version)
fn maskne64(x: u64, y: u64) -> u64 {
masknz64(x ^ y)
}

/// Return a [`u32::MAX`] mask if `condition` is non-zero, otherwise return zero for a zero input.
#[cfg(not(target_arch = "arm"))]
fn masknz32(condition: u32) -> u32 {
testnz32(condition).wrapping_neg()
let x = condition | condition.wrapping_neg(); // MSB of `x` now `1` if non-zero
let nz = core::hint::black_box(x >> (u32::BITS - 1)); // Extract MSB
nz.wrapping_neg()
}

/// Return a [`u64::MAX`] mask if `condition` is non-zero, otherwise return zero for a zero input.
#[cfg(not(target_arch = "arm"))]
fn masknz64(condition: u64) -> u64 {
testnz64(condition).wrapping_neg()
let x = condition | condition.wrapping_neg(); // MSB of `x` now `1` if non-zero
let nz = core::hint::black_box(x >> (u64::BITS - 1)); // Extract MSB
nz.wrapping_neg()
}

/// Optimized mask generation for ARM32 targets.
Expand Down Expand Up @@ -139,53 +163,76 @@ where
(a & !mask) | (b & mask)
}

/// Returns `1` if `x` is equal to `y`, otherwise returns `0` (32-bit version)
fn testeq32(x: u32, y: u32) -> Condition {
testne32(x, y) ^ 1
}

/// Returns `1` if `x` is equal to `y`, otherwise returns `0` (64-bit version)
fn testeq64(x: u64, y: u64) -> Condition {
testne64(x, y) ^ 1
}
#[cfg(test)]
mod tests {
// Spot check up to a given limit
const TEST_LIMIT: u32 = 65536;

/// Returns `0` if `x` is equal to `y`, otherwise returns `1` (32-bit version)
fn testne32(x: u32, y: u32) -> Condition {
(testnz32(x ^ y) & 0xFF) as Condition
}
#[test]
fn maskeq32() {
assert_eq!(super::maskeq32(0, 0), u32::MAX);
assert_eq!(super::maskeq32(1, 0), 0);
assert_eq!(super::maskeq32(0, 1), 0);
assert_eq!(super::maskeq32(1, 1), u32::MAX);
assert_eq!(super::maskeq32(u32::MAX, 1), 0);
assert_eq!(super::maskeq32(1, u32::MAX), 0);
assert_eq!(super::maskeq32(u32::MAX, u32::MAX), u32::MAX);
}

/// Returns `0` if `x` is equal to `y`, otherwise returns `1` (64-bit version)
fn testne64(x: u64, y: u64) -> Condition {
(testnz64(x ^ y) & 0xFF) as Condition
}
#[test]
fn maskeq64() {
assert_eq!(super::maskeq64(0, 0), u64::MAX);
assert_eq!(super::maskeq64(1, 0), 0);
assert_eq!(super::maskeq64(0, 1), 0);
assert_eq!(super::maskeq64(1, 1), u64::MAX);
assert_eq!(super::maskeq64(u64::MAX, 1), 0);
assert_eq!(super::maskeq64(1, u64::MAX), 0);
assert_eq!(super::maskeq64(u64::MAX, u64::MAX), u64::MAX);
}

/// Returns `0` if `x` is `0`, otherwise returns `1` (32-bit version)
fn testnz32(mut x: u32) -> u32 {
x |= x.wrapping_neg(); // MSB now set if non-zero
core::hint::black_box(x >> (u32::BITS - 1)) // Extract MSB
}
#[test]
fn maskne32() {
assert_eq!(super::maskne32(0, 0), 0);
assert_eq!(super::maskne32(1, 0), u32::MAX);
assert_eq!(super::maskne32(0, 1), u32::MAX);
assert_eq!(super::maskne32(1, 1), 0);
assert_eq!(super::maskne32(u32::MAX, 1), u32::MAX);
assert_eq!(super::maskne32(1, u32::MAX), u32::MAX);
assert_eq!(super::maskne32(u32::MAX, u32::MAX), 0);
}

/// Returns `0` if `x` is `0`, otherwise returns `1` (64-bit version)
fn testnz64(mut x: u64) -> u64 {
x |= x.wrapping_neg(); // MSB now set if non-zero (or unset if zero)
core::hint::black_box(x >> (u64::BITS - 1)) // Extract MSB
}
#[test]
fn maskne64() {
assert_eq!(super::maskne64(0, 0), 0);
assert_eq!(super::maskne64(1, 0), u64::MAX);
assert_eq!(super::maskne64(0, 1), u64::MAX);
assert_eq!(super::maskne64(1, 1), 0);
assert_eq!(super::maskne64(u64::MAX, 1), u64::MAX);
assert_eq!(super::maskne64(1, u64::MAX), u64::MAX);
assert_eq!(super::maskne64(u64::MAX, u64::MAX), 0);
}

#[cfg(test)]
mod tests {
#[test]
fn masknz32() {
assert_eq!(super::masknz32(0), 0);
for i in 1..=u8::MAX {
assert_eq!(super::masknz32(i.into()), u32::MAX);
for i in 1..=TEST_LIMIT {
assert_eq!(super::masknz32(i), u32::MAX);
}

for i in (u32::MAX - TEST_LIMIT)..=u32::MAX {
assert_eq!(super::masknz32(i), u32::MAX);
}
}

#[test]
fn masknz64() {
assert_eq!(super::masknz64(0), 0);
for i in 1..=u8::MAX {
assert_eq!(super::masknz64(i.into()), u64::MAX);
for i in 1..=(TEST_LIMIT as u64) {
assert_eq!(super::masknz64(i), u64::MAX);
}

for i in (u64::MAX - TEST_LIMIT as u64)..=u64::MAX {
assert_eq!(super::masknz64(i), u64::MAX);
}
}

Expand All @@ -196,65 +243,11 @@ mod tests {

assert_eq!(super::masksel(17u32, 101077u32, 0u32), 17u32);
assert_eq!(super::masksel(17u32, 101077u32, u32::MAX), 101077u32);
}

#[test]
fn testeq32() {
assert_eq!(super::testeq32(0, 0), 1);
assert_eq!(super::testeq32(1, 0), 0);
assert_eq!(super::testeq32(0, 1), 0);
assert_eq!(super::testeq32(1, 1), 1);
assert_eq!(super::testeq32(u32::MAX, 1), 0);
assert_eq!(super::testeq32(1, u32::MAX), 0);
assert_eq!(super::testeq32(u32::MAX, u32::MAX), 1);
}

#[test]
fn testeq64() {
assert_eq!(super::testeq64(0, 0), 1);
assert_eq!(super::testeq64(1, 0), 0);
assert_eq!(super::testeq64(0, 1), 0);
assert_eq!(super::testeq64(1, 1), 1);
assert_eq!(super::testeq64(u64::MAX, 1), 0);
assert_eq!(super::testeq64(1, u64::MAX), 0);
assert_eq!(super::testeq64(u64::MAX, u64::MAX), 1);
}

#[test]
fn testne32() {
assert_eq!(super::testne32(0, 0), 0);
assert_eq!(super::testne32(1, 0), 1);
assert_eq!(super::testne32(0, 1), 1);
assert_eq!(super::testne32(1, 1), 0);
assert_eq!(super::testne32(u32::MAX, 1), 1);
assert_eq!(super::testne32(1, u32::MAX), 1);
assert_eq!(super::testne32(u32::MAX, u32::MAX), 0);
}

#[test]
fn testne64() {
assert_eq!(super::testne64(0, 0), 0);
assert_eq!(super::testne64(1, 0), 1);
assert_eq!(super::testne64(0, 1), 1);
assert_eq!(super::testne64(1, 1), 0);
assert_eq!(super::testne64(u64::MAX, 1), 1);
assert_eq!(super::testne64(1, u64::MAX), 1);
assert_eq!(super::testne64(u64::MAX, u64::MAX), 0);
}

#[test]
fn testnz32() {
assert_eq!(super::testnz32(0), 0);
for i in 1..=u8::MAX {
assert_eq!(super::testnz32(i as u32), 1);
}
}

#[test]
fn testnz64() {
assert_eq!(super::testnz64(0), 0);
for i in 1..=u8::MAX {
assert_eq!(super::testnz64(i as u64), 1);
}
assert_eq!(super::masksel(129u64, 0xFFEEDDCCBBAA9988u64, 0u64), 129u64);
assert_eq!(
super::masksel(129u64, 0xFFEEDDCCBBAA9988u64, u64::MAX),
0xFFEEDDCCBBAA9988u64
);
}
}