42 lines
1.2 KiB
C
42 lines
1.2 KiB
C
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/*
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* Copyright (c) 2006-2022, RT-Thread Development Team
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* Change Logs:
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* Date Author Notes
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* 2022-08-01 GuEe-GUI first version
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*/
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#ifndef __UTIL_HASHMAP_H__
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#define __UTIL_HASHMAP_H__
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#include <rtdef.h>
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/*
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* http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
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*
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* GoldenRatio = ~(Math.pow(2, 32) / ((Math.sqrt(5) - 1) / 2)) + 1
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*/
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#define RT_HASHMAP_GOLDEN_RATIO_32 0x61C88647
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#define RT_HASHMAP_GOLDEN_RATIO_64 0X61C8864680B583EBULL
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rt_inline rt_uint32_t rt_hashmap_32(rt_uint32_t val, rt_uint32_t bits)
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{
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/* High bits are more random, so use them. */
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return (val * RT_HASHMAP_GOLDEN_RATIO_32) >> (32 - bits);
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}
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rt_inline rt_uint32_t rt_hashmap_64(rt_uint64_t val, rt_uint32_t bits)
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{
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#ifdef ARCH_CPU_64BIT
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/* 64x64-bit multiply is efficient on all 64-bit processors */
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return val * RT_HASHMAP_GOLDEN_RATIO_64 >> (64 - bits);
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#else
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/* Hash 64 bits using only 32x32-bit multiply. */
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return rt_hashmap_32((rt_uint32_t)val ^ ((val >> 32) * RT_HASHMAP_GOLDEN_RATIO_32), bits);
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#endif
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}
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#endif /* __UTIL_HASHMAP_H__ */
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