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0ae4460c61
Specializing cityhash4 on 32-bit architectures can reduce the size of stack frames as well as instruction count. This is a tiny but useful optimization, since some callers invoke it frequently. When specializing into 1/2/3/4-arg versions, the stack usage (in bytes) on some 32-bit arches are listed as follows: - x86: 32, 32, 32, 40 - arm-v7a: 20, 20, 28, 36 - riscv: 0, 0, 0, 16 - power: 16, 16, 16, 32 - mipsel: 8, 8, 8, 24 And each actual argument (even if passing 0) contributes evenly to the number of multiplication instructions generated: - x86: 9, 12, 15 ,18 - arm-v7a: 6, 8, 10, 12 - riscv / power: 12, 18, 20, 24 - mipsel: 9, 12, 15, 19 On 64-bit architectures, the tendencies are similar. But both stack sizes and instruction counts are significantly smaller thus negligible. Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <mav@FreeBSD.org> Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de> Signed-off-by: Shengqi Chen <harry-chen@outlook.com> Closes #16131 Closes #16483
97 lines
2.6 KiB
C
97 lines
2.6 KiB
C
// Copyright (c) 2011 Google, Inc.
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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// THE SOFTWARE.
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/*
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* Copyright (c) 2017 by Delphix. All rights reserved.
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*/
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#include <cityhash.h>
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#define HASH_K1 0xb492b66fbe98f273ULL
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#define HASH_K2 0x9ae16a3b2f90404fULL
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/*
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* Bitwise right rotate. Normally this will compile to a single
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* instruction.
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*/
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static inline uint64_t
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rotate(uint64_t val, int shift)
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{
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// Avoid shifting by 64: doing so yields an undefined result.
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return (shift == 0 ? val : (val >> shift) | (val << (64 - shift)));
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}
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static inline uint64_t
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cityhash_helper(uint64_t u, uint64_t v, uint64_t mul)
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{
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uint64_t a = (u ^ v) * mul;
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a ^= (a >> 47);
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uint64_t b = (v ^ a) * mul;
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b ^= (b >> 47);
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b *= mul;
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return (b);
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}
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static inline uint64_t
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cityhash_impl(uint64_t w1, uint64_t w2, uint64_t w3, uint64_t w4)
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{
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uint64_t mul = HASH_K2 + 64;
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uint64_t a = w1 * HASH_K1;
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uint64_t b = w2;
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uint64_t c = w4 * mul;
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uint64_t d = w3 * HASH_K2;
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return (cityhash_helper(rotate(a + b, 43) + rotate(c, 30) + d,
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a + rotate(b + HASH_K2, 18) + c, mul));
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}
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/*
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* Passing w as the 2nd argument could save one 64-bit multiplication.
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*/
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uint64_t
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cityhash1(uint64_t w)
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{
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return (cityhash_impl(0, w, 0, 0));
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}
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uint64_t
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cityhash2(uint64_t w1, uint64_t w2)
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{
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return (cityhash_impl(w1, w2, 0, 0));
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}
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uint64_t
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cityhash3(uint64_t w1, uint64_t w2, uint64_t w3)
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{
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return (cityhash_impl(w1, w2, w3, 0));
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}
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uint64_t
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cityhash4(uint64_t w1, uint64_t w2, uint64_t w3, uint64_t w4)
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{
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return (cityhash_impl(w1, w2, w3, w4));
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}
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#if defined(_KERNEL)
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EXPORT_SYMBOL(cityhash1);
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EXPORT_SYMBOL(cityhash2);
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EXPORT_SYMBOL(cityhash3);
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EXPORT_SYMBOL(cityhash4);
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#endif
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