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Update README
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‎README.md

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@@ -25,39 +25,57 @@ table implementation in the Rust standard library.
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## Features
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- Drop-in replacement for the standard library `HashMap` and `HashSet` types.
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- Uses `FxHash` as the default hasher, which is much faster than SipHash.
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- Around 2x faster than `FxHashMap` and 8x faster than the standard `HashMap`.
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- Uses `AHash` as the default hasher, which is much faster than SipHash.
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- Around 2x faster than the previous standard library `HashMap`.
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- Lower memory usage: only 1 byte of overhead per entry instead of 8.
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- Compatible with `#[no_std]` (currently requires nightly for the `alloc` crate).
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- Compatible with `#[no_std]` (but requires a global allocator with the `alloc` crate).
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- Empty hash maps do not allocate any memory.
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- SIMD lookups to scan multiple hash entries in parallel.
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## Performance
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Compared to the previous implementation of `std::collections::HashMap`:
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Compared to the previous implementation of `std::collections::HashMap` (Rust 1.35).
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With the hashbrown default AHash hasher:
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```text
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name stdhash ns/iter hashbrown ns/iter diff ns/iter diff % speedup
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find_existing 23,831 2,935 -20,896 -87.68% x 8.12
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find_nonexisting 25,326 2,283 -23,043 -90.99% x 11.09
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get_remove_insert 124 25 -99 -79.84% x 4.96
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grow_by_insertion 197 177 -20 -10.15% x 1.11
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hashmap_as_queue 72 18 -54 -75.00% x 4.00
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new_drop 14 0 -14 -100.00% x inf
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new_insert_drop 78 55 -23 -29.49% x 1.42
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name oldstdhash ns/iter hashbrown ns/iter diff ns/iter diff % speedup
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insert_ahash_highbits 20,846 7,397 -13,449 -64.52% x 2.82
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insert_ahash_random 20,515 7,796 -12,719 -62.00% x 2.63
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insert_ahash_serial 21,668 7,264 -14,404 -66.48% x 2.98
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insert_erase_ahash_highbits 29,570 17,498 -12,072 -40.83% x 1.69
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insert_erase_ahash_random 39,569 17,474 -22,095 -55.84% x 2.26
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insert_erase_ahash_serial 32,073 17,332 -14,741 -45.96% x 1.85
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iter_ahash_highbits 1,572 2,087 515 32.76% x 0.75
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iter_ahash_random 1,609 2,074 465 28.90% x 0.78
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iter_ahash_serial 2,293 2,120 -173 -7.54% x 1.08
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lookup_ahash_highbits 3,460 4,403 943 27.25% x 0.79
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lookup_ahash_random 6,377 3,911 -2,466 -38.67% x 1.63
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lookup_ahash_serial 3,629 3,586 -43 -1.18% x 1.01
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lookup_fail_ahash_highbits 5,286 3,411 -1,875 -35.47% x 1.55
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lookup_fail_ahash_random 12,365 4,171 -8,194 -66.27% x 2.96
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lookup_fail_ahash_serial 4,902 3,240 -1,662 -33.90% x 1.51
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```
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Compared to `rustc_hash::FxHashMap` (standard `HashMap` using `FxHash` instead of `SipHash`):
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With the libstd default SipHash hasher:
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```text
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name fxhash ns/iter hashbrown ns/iter diff ns/iter diff % speedup
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find_existing 5,951 2,935 -3,016 -50.68% x 2.03
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find_nonexisting 4,637 2,283 -2,354 -50.77% x 2.03
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get_remove_insert 29 25 -4 -13.79% x 1.16
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grow_by_insertion 160 177 17 10.62% x 0.90
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hashmap_as_queue 22 18 -4 -18.18% x 1.22
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new_drop 9 0 -9 -100.00% x inf
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new_insert_drop 64 55 -9 -14.06% x 1.16
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name oldstdhash ns/iter hashbrown ns/iter diff ns/iter diff % speedup
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insert_std_highbits 32,598 20,199 -12,399 -38.04% x 1.61
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insert_std_random 29,824 20,760 -9,064 -30.39% x 1.44
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insert_std_serial 33,151 17,256 -15,895 -47.95% x 1.92
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insert_erase_std_highbits 74,731 48,735 -25,996 -34.79% x 1.53
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insert_erase_std_random 73,828 47,649 -26,179 -35.46% x 1.55
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insert_erase_std_serial 73,864 40,147 -33,717 -45.65% x 1.84
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iter_std_highbits 1,518 2,264 746 49.14% x 0.67
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iter_std_random 1,502 2,414 912 60.72% x 0.62
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iter_std_serial 6,361 2,118 -4,243 -66.70% x 3.00
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lookup_std_highbits 21,705 16,962 -4,743 -21.85% x 1.28
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lookup_std_random 21,654 17,158 -4,496 -20.76% x 1.26
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lookup_std_serial 18,726 14,509 -4,217 -22.52% x 1.29
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lookup_fail_std_highbits 25,852 17,323 -8,529 -32.99% x 1.49
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lookup_fail_std_random 25,913 17,760 -8,153 -31.46% x 1.46
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lookup_fail_std_serial 22,648 14,839 -7,809 -34.48% x 1.53
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```
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## Usage
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This crate has the following Cargo features:
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- `nightly`: Enables nightly-only features: `no_std` support and `#[may_dangle]`.
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- `nightly`: Enables nightly-only features: `#[may_dangle]`.
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- `serde`: Enables serde serialization support.
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- `rayon`: Enables rayon parallel iterator support.
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‎src/map.rs

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@@ -18,7 +18,7 @@ pub enum DefaultHashBuilder {}
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/// A hash map implemented with quadratic probing and SIMD lookup.
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///
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/// The default hashing algorithm is currently `fx`, though this is
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/// The default hashing algorithm is currently [AHash], though this is
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/// subject to change at any point in the future. This hash function is very
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/// fast for all types of keys, but this algorithm will typically *not* protect
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/// against attacks such as HashDoS.
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/// [`with_hasher`]: #method.with_hasher
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/// [`with_capacity_and_hasher`]: #method.with_capacity_and_hasher
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/// [`fnv`]: https://crates.io/crates/fnv
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/// [AHash]: https://crates.io/crates/ahash
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///
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/// ```
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/// use hashbrown::HashMap;

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