b8536c1aa1
Add "integer square root" method to integer primitive types For every suffix `N` among `8`, `16`, `32`, `64`, `128` and `size`, this PR adds the methods ```rust const fn uN::isqrt() -> uN; const fn iN::isqrt() -> iN; const fn iN::checked_isqrt() -> Option<iN>; ``` to compute the [integer square root](https://en.wikipedia.org/wiki/Integer_square_root), addressing issue #89273. The implementation is based on the [base 2 digit-by-digit algorithm](https://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Binary_numeral_system_(base_2)) on Wikipedia, which after some benchmarking has proved to be faster than both binary search and Heron's/Newton's method. I haven't had the time to understand and port [this code](http://atoms.alife.co.uk/sqrt/SquareRoot.java) based on lookup tables instead, but I'm not sure whether it's worth complicating such a function this much for relatively little benefit.
181 lines
4.6 KiB
Rust
181 lines
4.6 KiB
Rust
#![feature(alloc_layout_extra)]
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#![feature(array_chunks)]
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#![feature(array_methods)]
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#![feature(array_windows)]
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#![feature(ascii_char)]
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#![feature(ascii_char_variants)]
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#![feature(bigint_helper_methods)]
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#![feature(cell_update)]
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#![feature(const_align_offset)]
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#![feature(const_assume)]
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#![feature(const_align_of_val_raw)]
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#![feature(const_black_box)]
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#![feature(const_caller_location)]
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#![feature(const_cell_into_inner)]
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#![feature(const_hash)]
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#![feature(const_heap)]
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#![feature(const_maybe_uninit_as_mut_ptr)]
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#![feature(const_maybe_uninit_assume_init_read)]
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#![feature(const_nonnull_new)]
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#![feature(const_pointer_byte_offsets)]
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#![feature(const_pointer_is_aligned)]
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#![feature(const_ptr_as_ref)]
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#![feature(const_ptr_write)]
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#![feature(const_trait_impl)]
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#![feature(const_likely)]
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#![feature(const_location_fields)]
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#![feature(core_intrinsics)]
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#![feature(core_private_bignum)]
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#![feature(core_private_diy_float)]
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#![feature(dec2flt)]
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#![feature(div_duration)]
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#![feature(duration_consts_float)]
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#![feature(duration_constants)]
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#![feature(exact_size_is_empty)]
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#![feature(extern_types)]
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#![feature(flt2dec)]
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#![feature(fmt_internals)]
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#![feature(float_minimum_maximum)]
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#![feature(future_join)]
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#![feature(generic_assert_internals)]
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#![feature(array_try_from_fn)]
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#![feature(hasher_prefixfree_extras)]
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#![feature(hashmap_internals)]
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#![feature(try_find)]
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#![feature(inline_const)]
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#![feature(is_sorted)]
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#![feature(layout_for_ptr)]
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#![feature(pattern)]
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#![feature(sort_internals)]
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#![feature(slice_take)]
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#![feature(slice_from_ptr_range)]
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#![feature(split_as_slice)]
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#![feature(maybe_uninit_uninit_array)]
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#![feature(maybe_uninit_write_slice)]
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#![feature(maybe_uninit_uninit_array_transpose)]
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#![feature(min_specialization)]
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#![feature(numfmt)]
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#![feature(num_midpoint)]
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#![feature(isqrt)]
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#![feature(step_trait)]
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#![feature(str_internals)]
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#![feature(std_internals)]
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#![feature(test)]
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#![feature(trusted_len)]
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#![feature(try_blocks)]
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#![feature(try_trait_v2)]
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#![feature(slice_internals)]
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#![feature(slice_partition_dedup)]
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#![feature(ip)]
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#![feature(ip_in_core)]
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#![feature(iter_advance_by)]
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#![feature(iter_array_chunks)]
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#![feature(iter_collect_into)]
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#![feature(iter_partition_in_place)]
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#![feature(iter_intersperse)]
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#![feature(iter_is_partitioned)]
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#![feature(iter_next_chunk)]
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#![feature(iter_order_by)]
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#![feature(iter_repeat_n)]
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#![feature(iterator_try_collect)]
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#![feature(iterator_try_reduce)]
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#![feature(const_ip)]
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#![feature(const_ipv4)]
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#![feature(const_ipv6)]
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#![feature(const_mut_refs)]
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#![feature(const_pin)]
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#![feature(const_waker)]
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#![feature(never_type)]
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#![feature(unwrap_infallible)]
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#![feature(pointer_byte_offsets)]
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#![feature(pointer_is_aligned)]
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#![feature(portable_simd)]
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#![feature(ptr_metadata)]
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#![feature(lazy_cell)]
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#![feature(unsized_tuple_coercion)]
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#![feature(const_option)]
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#![feature(const_option_ext)]
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#![feature(const_result)]
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#![cfg_attr(target_has_atomic = "128", feature(integer_atomics))]
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#![cfg_attr(test, feature(cfg_match))]
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#![feature(int_roundings)]
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#![feature(slice_group_by)]
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#![feature(split_array)]
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#![feature(strict_provenance)]
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#![feature(strict_provenance_atomic_ptr)]
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#![feature(trusted_random_access)]
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#![feature(unsize)]
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#![feature(const_array_from_ref)]
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#![feature(const_slice_from_ref)]
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#![feature(waker_getters)]
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#![feature(slice_flatten)]
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#![feature(error_generic_member_access)]
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#![feature(error_in_core)]
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#![feature(trait_upcasting)]
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#![feature(utf8_chunks)]
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#![feature(is_ascii_octdigit)]
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#![feature(get_many_mut)]
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#![feature(offset_of)]
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#![feature(iter_map_windows)]
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#![deny(unsafe_op_in_unsafe_fn)]
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#![deny(fuzzy_provenance_casts)]
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extern crate test;
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mod alloc;
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mod any;
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mod array;
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mod ascii;
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mod asserting;
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mod atomic;
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mod bool;
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mod cell;
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mod char;
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mod clone;
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mod cmp;
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mod const_ptr;
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mod convert;
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mod fmt;
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mod future;
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mod hash;
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mod intrinsics;
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mod iter;
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mod lazy;
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#[cfg(test)]
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mod macros;
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mod manually_drop;
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mod mem;
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mod net;
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mod nonzero;
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mod num;
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mod ops;
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mod option;
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mod panic;
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mod pattern;
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mod pin;
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mod pin_macro;
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mod ptr;
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mod result;
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mod simd;
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mod slice;
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mod str;
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mod str_lossy;
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mod task;
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mod time;
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mod tuple;
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mod unicode;
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mod waker;
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/// Copied from `std::test_helpers::test_rng`, see that function for rationale.
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#[track_caller]
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#[allow(dead_code)] // Not used in all configurations.
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pub(crate) fn test_rng() -> rand_xorshift::XorShiftRng {
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use core::hash::{BuildHasher, Hash, Hasher};
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let mut hasher = std::collections::hash_map::RandomState::new().build_hasher();
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core::panic::Location::caller().hash(&mut hasher);
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let hc64 = hasher.finish();
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let seed_vec = hc64.to_le_bytes().into_iter().chain(0u8..8).collect::<Vec<u8>>();
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let seed: [u8; 16] = seed_vec.as_slice().try_into().unwrap();
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rand::SeedableRng::from_seed(seed)
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}
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