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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,140 @@ | ||
| // Part of dump1090, a Mode S message decoder for RTLSDR devices. | ||
| // | ||
| // icao_filter.c: hashtable for ICAO addresses | ||
| // | ||
| // Copyright (c) 2014,2015 Oliver Jowett <oliver@mutability.co.uk> | ||
| // | ||
| // This file is free software: you may copy, redistribute and/or modify it | ||
| // under the terms of the GNU General Public License as published by the | ||
| // Free Software Foundation, either version 2 of the License, or (at your | ||
| // option) any later version. | ||
| // | ||
| // This file is distributed in the hope that it will be useful, but | ||
| // WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | ||
| // General Public License for more details. | ||
| // | ||
| // You should have received a copy of the GNU General Public License | ||
| // along with this program. If not, see <http://www.gnu.org/licenses/>. | ||
|
|
||
| #include "dump1090.h" | ||
|
|
||
| // hash table size, must be a power of two: | ||
| #define ICAO_FILTER_SIZE 4096 | ||
|
|
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| // Seconds between filter expiry flips: | ||
| #define MODES_ICAO_FILTER_TTL 60 | ||
|
|
||
| // Open-addressed hash table with linear probing. | ||
| // We store each address twice to handle Address/Parity and Data/Parity | ||
| // which need to match on a partial address (top 16 bits only). | ||
|
|
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| // Maintain two tables and switch between them to age out entries. | ||
|
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| static uint32_t icao_filter_a[ICAO_FILTER_SIZE]; | ||
| static uint32_t icao_filter_b[ICAO_FILTER_SIZE]; | ||
| static uint32_t *icao_filter_active; | ||
|
|
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| static uint32_t icaoHash(uint32_t a) | ||
| { | ||
| // Jenkins one-at-a-time hash, unrolled for 3 bytes | ||
| uint32_t hash = 0; | ||
|
|
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| hash += a & 0xff; | ||
| hash += hash << 10; | ||
| hash ^= hash >> 6; | ||
|
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| hash += (a >> 8) & 0xff; | ||
| hash += (hash << 10); | ||
| hash ^= (hash >> 6); | ||
|
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| hash += (a >> 16) & 0xff; | ||
| hash += (hash << 10); | ||
| hash ^= (hash >> 6); | ||
|
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| hash += (hash << 3); | ||
| hash ^= (hash >> 11); | ||
| hash += (hash << 15); | ||
|
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| return hash & (ICAO_FILTER_SIZE-1); | ||
| } | ||
|
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| void icaoFilterInit() | ||
| { | ||
| memset(icao_filter_a, 0, sizeof(icao_filter_a)); | ||
| memset(icao_filter_b, 0, sizeof(icao_filter_b)); | ||
| icao_filter_active = icao_filter_a; | ||
| } | ||
|
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| void icaoFilterAdd(uint32_t addr) | ||
| { | ||
| uint32_t h = icaoHash(addr); | ||
| while (icao_filter_active[h] && icao_filter_active[h] != addr) | ||
| h = (h+1) & (ICAO_FILTER_SIZE-1); | ||
| if (!icao_filter_active[h]) | ||
| icao_filter_active[h] = addr; | ||
|
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| // also add with a zeroed top byte, for handling DF20/21 with Data Parity | ||
| h = icaoHash(addr & 0x00ffff); | ||
| while (icao_filter_active[h] && (icao_filter_active[h] & 0x00ffff) != (addr & 0x00ffff)) | ||
| h = (h+1) & (ICAO_FILTER_SIZE-1); | ||
| if (!icao_filter_active[h]) | ||
| icao_filter_active[h] = addr; | ||
| } | ||
|
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||
| int icaoFilterTest(uint32_t addr) | ||
| { | ||
| uint32_t h, h0; | ||
|
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| h0 = h = icaoHash(addr); | ||
| while (icao_filter_a[h] && icao_filter_a[h] != addr) | ||
| h = (h+1) & (ICAO_FILTER_SIZE-1); | ||
| if (icao_filter_a[h]) | ||
| return 1; | ||
|
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| h = h0; | ||
| while (icao_filter_b[h] && icao_filter_b[h] != addr) | ||
| h = (h+1) & (ICAO_FILTER_SIZE-1); | ||
| if (icao_filter_b[h]) | ||
| return 1; | ||
|
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||
| return 0; | ||
| } | ||
|
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| uint32_t icaoFilterTestFuzzy(uint32_t partial) | ||
| { | ||
| uint32_t h, h0; | ||
|
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| partial &= 0x00ffff; | ||
| h0 = h = icaoHash(partial); | ||
| while (icao_filter_a[h] && (icao_filter_a[h] & 0x00ffff) != partial) | ||
| h = (h+1) & (ICAO_FILTER_SIZE-1); | ||
| if (icao_filter_a[h]) | ||
| return icao_filter_a[h]; | ||
|
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| h = h0; | ||
| while (icao_filter_b[h] && (icao_filter_b[h] & 0x00ffff) != partial) | ||
| h = (h+1) & (ICAO_FILTER_SIZE-1); | ||
| if (icao_filter_b[h]) | ||
| return icao_filter_b[h]; | ||
|
|
||
| return 0; | ||
| } | ||
|
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| // call this periodically: | ||
| void icaoFilterExpire() | ||
| { | ||
| static time_t next_flip = 0; | ||
| time_t now = time(NULL); | ||
|
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| if (now >= next_flip) { | ||
| if (icao_filter_active == icao_filter_a) { | ||
| memset(icao_filter_b, 0, sizeof(icao_filter_b)); | ||
| icao_filter_active = icao_filter_b; | ||
| } else { | ||
| memset(icao_filter_a, 0, sizeof(icao_filter_a)); | ||
| icao_filter_active = icao_filter_a; | ||
| } | ||
| next_flip = now + MODES_ICAO_FILTER_TTL; | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,41 @@ | ||
| // Part of dump1090, a Mode S message decoder for RTLSDR devices. | ||
| // | ||
| // icao_filter.c: prototypes for ICAO address hashtable | ||
| // | ||
| // Copyright (c) 2014,2015 Oliver Jowett <oliver@mutability.co.uk> | ||
| // | ||
| // This file is free software: you may copy, redistribute and/or modify it | ||
| // under the terms of the GNU General Public License as published by the | ||
| // Free Software Foundation, either version 2 of the License, or (at your | ||
| // option) any later version. | ||
| // | ||
| // This file is distributed in the hope that it will be useful, but | ||
| // WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | ||
| // General Public License for more details. | ||
| // | ||
| // You should have received a copy of the GNU General Public License | ||
| // along with this program. If not, see <http://www.gnu.org/licenses/>. | ||
|
|
||
| #ifndef DUMP1090_ICAO_FILTER_H | ||
| #define DUMP1090_ICAO_FILTER_H | ||
|
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| // Call once: | ||
| void icaoFilterInit(); | ||
|
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| // Add an address to the filter | ||
| void icaoFilterAdd(uint32_t addr); | ||
|
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| // Test if the given address matches the filter | ||
| int icaoFilterTest(uint32_t addr); | ||
|
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| // Test if the top 16 bits match any previously added address. | ||
| // If they do, returns an arbitrary one of the matched | ||
| // addresses. Returns 0 on failure. | ||
| uint32_t icaoFilterTestFuzzy(uint32_t partial); | ||
|
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| // Call this periodically to allow the filter to expire | ||
| // old entries. | ||
| void icaoFilterExpire(); | ||
|
|
||
| #endif |
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