414 lines
9.5 KiB
Rust
414 lines
9.5 KiB
Rust
#![allow(unused_features)]
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#![cfg_attr(not(test), no_std)]
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#![feature(asm)]
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#![feature(core_intrinsics)]
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#![feature(naked_functions)]
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// TODO(rust-lang/rust#35021) uncomment when that PR lands
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// #![feature(rustc_builtins)]
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#[cfg(test)]
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extern crate core;
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#[cfg(test)]
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#[macro_use]
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extern crate quickcheck;
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#[cfg(target_arch = "arm")]
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pub mod arm;
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#[cfg(test)]
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mod test;
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/// Trait for some basic operations on integers
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trait Int {
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fn bits() -> usize;
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}
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// TODO: Once i128/u128 support lands, we'll want to add impls for those as well
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impl Int for u32 {
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fn bits() -> usize {
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32
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}
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}
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impl Int for i32 {
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fn bits() -> usize {
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32
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}
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}
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impl Int for u64 {
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fn bits() -> usize {
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64
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}
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}
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impl Int for i64 {
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fn bits() -> usize {
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64
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}
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}
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/// Trait to convert an integer to/from smaller parts
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trait LargeInt {
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type LowHalf;
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type HighHalf;
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fn low(self) -> Self::LowHalf;
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fn high(self) -> Self::HighHalf;
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fn from_parts(low: Self::LowHalf, high: Self::HighHalf) -> Self;
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}
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// TODO: Once i128/u128 support lands, we'll want to add impls for those as well
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impl LargeInt for u64 {
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type LowHalf = u32;
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type HighHalf = u32;
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fn low(self) -> u32 {
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self as u32
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}
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fn high(self) -> u32 {
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(self >> 32) as u32
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}
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fn from_parts(low: u32, high: u32) -> u64 {
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low as u64 | ((high as u64) << 32)
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}
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}
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impl LargeInt for i64 {
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type LowHalf = u32;
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type HighHalf = i32;
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fn low(self) -> u32 {
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self as u32
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}
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fn high(self) -> i32 {
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(self >> 32) as i32
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}
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fn from_parts(low: u32, high: i32) -> i64 {
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low as i64 | ((high as i64) << 32)
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}
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}
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macro_rules! absv_i2 {
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($intrinsic:ident : $ty:ty) => {
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#[no_mangle]
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pub extern "C" fn $intrinsic(x: $ty) -> $ty {
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let n = <$ty>::bits();
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if x == 1 << (n - 1) {
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panic!();
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}
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let y = x >> (n - 1);
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(x ^ y) - y
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}
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}
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}
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absv_i2!(__absvsi2: i32);
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absv_i2!(__absvdi2: i64);
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// TODO(rust-lang/35118)?
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// absv_i2!(__absvti2, i128);
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/// Return `n / d` and `*rem = n % d`
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#[no_mangle]
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pub extern "C" fn __udivmoddi4(n: u64, d: u64, rem: Option<&mut u64>) -> u64 {
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use core::ops::{Index, IndexMut, RangeFull};
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#[cfg(target_endian = "little")]
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#[repr(C)]
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struct U64 {
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low: u32,
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high: u32,
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}
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#[cfg(target_endian = "big")]
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#[repr(C)]
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struct U64 {
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high: u32,
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low: u32,
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}
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impl Index<RangeFull> for U64 {
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type Output = u64;
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fn index(&self, _: RangeFull) -> &u64 {
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unsafe { &*(self as *const _ as *const u64) }
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}
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}
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impl IndexMut<RangeFull> for U64 {
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fn index_mut(&mut self, _: RangeFull) -> &mut u64 {
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unsafe { &mut *(self as *const _ as *mut u64) }
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}
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}
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let u32_bits = u32::bits() as u32;
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let u64_bits = u64::bits() as u32;
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// NOTE X is unknown, K != 0
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if n.high() == 0 {
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if d.high() == 0 {
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// 0 X
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// ---
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// 0 X
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if let Some(rem) = rem {
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*rem = u64::from(n.low() % d.low());
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}
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return u64::from(n.low() / d.low());
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} else
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// d.high() != 0
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{
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// 0 X
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// ---
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// K X
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if let Some(rem) = rem {
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*rem = u64::from(n.low());
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}
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return 0;
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};
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}
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let mut sr;
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let mut q = U64 { low: 0, high: 0 };
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let mut r = U64 { low: 0, high: 0 };
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// n.high() != 0
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if d.low() == 0 {
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if d.high() == 0 {
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// K X
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// ---
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// 0 0
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// NOTE copied verbatim from compiler-rt. This probably lets the intrinsic decide how to
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// handle the division by zero (SIGFPE, 0, etc.). But this part shouldn't be reachable
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// from safe code.
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if let Some(rem) = rem {
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*rem = u64::from(n.high() % d.low());
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}
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return u64::from(n.high() / d.low());
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}
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// d.high() != 0
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if n.low() == 0 {
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// K 0
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// ---
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// K 0
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if let Some(rem) = rem {
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*rem = U64 {
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low: 0,
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high: n.high() % d.high(),
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}[..];
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}
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return u64::from(n.high() / d.high());
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}
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// n.low() != 0
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// K K
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// ---
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// K 0
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if d.high().is_power_of_two() {
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if let Some(rem) = rem {
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*rem = U64 {
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low: n.low(),
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high: n.high() & (d.high() - 1),
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}[..];
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}
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return u64::from(n.high() >> d.high().trailing_zeros());
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}
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sr = d.high().leading_zeros().wrapping_sub(n.high().leading_zeros());
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// D > N
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if sr > u32_bits - 2 {
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if let Some(rem) = rem {
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*rem = n;
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}
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return 0;
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}
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sr = sr + 1;
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// 1 <= sr <= u32_bits - 1
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// q = n << (u64_bits - sr);
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q.low = 0;
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q.high = n.low() << (u32_bits - sr);
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// r = n >> sr
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r.high = n.high() >> sr;
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r.low = (n.high() << (u32_bits - sr)) | (n.low() >> sr);
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} else
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// d.low() != 0
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{
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if d.high() == 0 {
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// K X
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// ---
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// 0 K
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if d.low().is_power_of_two() {
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if let Some(rem) = rem {
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*rem = u64::from(n.low() & (d.low() - 1));
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}
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if d.low() == 1 {
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return n;
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} else {
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let sr = d.low().trailing_zeros();
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return U64 {
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low: (n.high() << (u32_bits - sr)) | (n.low() >> sr),
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high: n.high() >> sr,
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}[..];
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};
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}
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sr = 1 + u32_bits + d.low().leading_zeros() - n.high().leading_zeros();
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// 2 <= sr <= u64_bits - 1
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// q = n << (u64_bits - sr)
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// r = n >> sr;
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if sr == u32_bits {
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q.low = 0;
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q.high = n.low();
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r.high = 0;
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r.low = n.high();
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} else if sr < u32_bits
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// 2 <= sr <= u32_bits - 1
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{
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q.low = 0;
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q.high = n.low() << (u32_bits - sr);
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r.high = n.high() >> sr;
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r.low = (n.high() << (u32_bits - sr)) | (n.low() >> sr);
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} else
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// u32_bits + 1 <= sr <= u64_bits - 1
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{
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q.low = n.low() << (u64_bits - sr);
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q.high = (n.high() << (u64_bits - sr)) | (n.low() >> (sr - u32_bits));
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r.high = 0;
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r.low = n.high() >> (sr - u32_bits);
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}
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} else
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// d.high() != 0
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{
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// K X
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// ---
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// K K
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sr = d.high().leading_zeros().wrapping_sub(n.high().leading_zeros());
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// D > N
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if sr > u32_bits - 1 {
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if let Some(rem) = rem {
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*rem = n;
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return 0;
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}
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}
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sr += 1;
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// 1 <= sr <= u32_bits
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// q = n << (u64_bits - sr)
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q.low = 0;
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if sr == u32_bits {
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q.high = n.low();
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r.high = 0;
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r.low = n.high();
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} else {
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q.high = n.low() << (u32_bits - sr);
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r.high = n.high() >> sr;
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r.low = (n.high() << (u32_bits - sr)) | (n.low() >> sr);
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}
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}
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}
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// Not a special case
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// q and r are initialized with
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// q = n << (u64_bits - sr)
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// r = n >> sr
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// 1 <= sr <= u64_bits - 1
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let mut carry = 0;
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for _ in 0..sr {
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// r:q = ((r:q) << 1) | carry
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r[..] = (r[..] << 1) | (q[..] >> 63);
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q[..] = (q[..] << 1) | carry as u64;
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// carry = 0
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// if r >= d {
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// r -= d;
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// carry = 1;
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// }
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let s = (d.wrapping_sub(r[..]).wrapping_sub(1)) as i64 >> (u64_bits - 1);
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carry = (s & 1) as u32;
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r[..] -= d & s as u64;
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}
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q[..] = (q[..] << 1) | carry as u64;
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if let Some(rem) = rem {
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*rem = r[..];
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}
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q[..]
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}
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/// Return `n / d` and `*rem = n % d`
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#[no_mangle]
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pub extern "C" fn __udivmodsi4(a: u32, b: u32, rem: Option<&mut u32>) -> u32 {
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let d = __udivsi3(a, b);
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if let Some(rem) = rem {
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*rem = a - (d * b);
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}
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return d;
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}
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/// Return `n / d`
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#[no_mangle]
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pub extern "C" fn __udivsi3(n: u32, d: u32) -> u32 {
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let u32_bits = u32::bits() as u32;
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// Special cases
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if d == 0 {
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return 0; // ?!
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}
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if n == 0 {
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return 0;
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}
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let mut sr = d.leading_zeros().wrapping_sub(n.leading_zeros());
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// d > n
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if sr > u32_bits - 1 {
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return 0;
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}
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// d == 1
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if sr == u32_bits - 1 {
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return n;
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}
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sr = sr + 1;
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// 1 <= sr <= u32_bits - 1
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let mut q = n << (u32_bits - sr);
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let mut r = n >> sr;
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let mut carry = 0;
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for _ in 0..sr {
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// r:q = ((r:q) << 1) | carry
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r = (r << 1) | (q >> (u32_bits - 1));
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q = (q << 1) | carry;
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// carry = 0;
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// if r > d {
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// r -= d;
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// carry = 1;
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// }
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let s = (d.wrapping_sub(r).wrapping_sub(1)) as i32 >> (u32_bits - 1);
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carry = (s & 1) as u32;
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r -= d & s as u32;
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}
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q = (q << 1) | carry;
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q
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}
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