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perf: specialize shifts for small sizes #563

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perf: specialize shifts for small sizes #563

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62 changes: 62 additions & 0 deletions src/bits.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -327,6 +327,37 @@ impl<const BITS: usize, const LIMBS: usize> Uint<BITS, LIMBS> {
#[inline]
#[must_use]
pub const fn overflowing_shl(self, rhs: usize) -> (Self, bool) {
as_primitives!(self, {
u64(x) => {
let (limbs, bits) = (rhs / 64, rhs % 64);
if limbs >= 1 {
return (Self::ZERO, x != 0);
}
let carry = (x >> (63 - bits)) >> 1;
let mut r = Self::ZERO;
r.limbs[0] = (x << bits) & Self::MASK;
return (r, carry != 0);
},
u128(x) => {
let (limbs, bits) = (rhs / 64, rhs % 64);
if limbs >= 2 {
return (Self::ZERO, x != 0);
}
if limbs == 0 {
let carry = (x >> (127 - bits)) >> 1;
let shifted = x << bits;
let mut r = Self::ZERO;
r.limbs[0] = shifted as u64;
r.limbs[1] = (shifted >> 64) as u64 & Self::MASK;
return (r, carry != 0);
}
let lo = x as u64 as u128;
let carry = (lo >> (63 - bits)) >> 1;
let mut r = Self::ZERO;
r.limbs[1] = (lo << bits) as u64 & Self::MASK;
return (r, carry != 0);
},
});
let (limbs, bits) = (rhs / 64, rhs % 64);
if limbs >= LIMBS {
return (Self::ZERO, !self.const_is_zero());
Expand Down Expand Up @@ -410,6 +441,37 @@ impl<const BITS: usize, const LIMBS: usize> Uint<BITS, LIMBS> {
#[inline]
#[must_use]
pub const fn overflowing_shr(self, rhs: usize) -> (Self, bool) {
as_primitives!(self, {
u64(x) => {
let (limbs, bits) = (rhs / 64, rhs % 64);
if limbs >= 1 {
return (Self::ZERO, x != 0);
}
let carry = (x << (63 - bits)) << 1;
let mut r = Self::ZERO;
r.limbs[0] = x >> bits;
return (r, carry != 0);
},
u128(x) => {
let (limbs, bits) = (rhs / 64, rhs % 64);
if limbs >= 2 {
return (Self::ZERO, x != 0);
}
if limbs == 0 {
let carry = (x << (127 - bits)) << 1;
let shifted = x >> bits;
let mut r = Self::ZERO;
r.limbs[0] = shifted as u64;
r.limbs[1] = (shifted >> 64) as u64;
return (r, carry != 0);
}
let hi = (x >> 64) as u64;
let carry = (hi << (63 - bits)) << 1;
let mut r = Self::ZERO;
r.limbs[0] = hi >> bits;
return (r, carry != 0);
},
});
let (limbs, bits) = (rhs / 64, rhs % 64);
if limbs >= LIMBS {
return (Self::ZERO, !self.const_is_zero());
Expand Down
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