src/hash.c

/*
 * Hash function implementation
 *
 * See mailing list thread on "Consistent hashing alternative to sdbm"
 * http://marc.info/?l=haproxy&m=138213693909219
 *
 * Copyright 2000-2010 Willy Tarreau <w@1wt.eu>
 *
 * This program is free software; you can redistribute it 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.
 *
 */


#include <common/hash.h>


unsigned int hash_wt6(const char *key, int len)
{
	unsigned h0 = 0xa53c965aUL;
	unsigned h1 = 0x5ca6953aUL;
	unsigned step0 = 6;
	unsigned step1 = 18;

	for (; len > 0; len--) {
		unsigned int t;

		t = ((unsigned int)*key);
		key++;

		h0 = ~(h0 ^ t);
		h1 = ~(h1 + t);

		t  = (h1 << step0) | (h1 >> (32-step0));
		h1 = (h0 << step1) | (h0 >> (32-step1));
		h0 = t;

		t = ((h0 >> 16) ^ h1) & 0xffff;
		step0 = t & 0x1F;
		step1 = t >> 11;
	}
	return h0 ^ h1;
}

unsigned int hash_djb2(const char *key, int len)
{
	unsigned int hash = 5381;

	/* the hash unrolled eight times */
	for (; len >= 8; len -= 8) {
		hash = ((hash << 5) + hash) + *key++;
		hash = ((hash << 5) + hash) + *key++;
		hash = ((hash << 5) + hash) + *key++;
		hash = ((hash << 5) + hash) + *key++;
		hash = ((hash << 5) + hash) + *key++;
		hash = ((hash << 5) + hash) + *key++;
		hash = ((hash << 5) + hash) + *key++;
		hash = ((hash << 5) + hash) + *key++;
	}
	switch (len) {
		case 7: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
		case 6: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
		case 5: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
		case 4: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
		case 3: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
		case 2: hash = ((hash << 5) + hash) + *key++; /* fallthrough... */
		case 1: hash = ((hash << 5) + hash) + *key++; break;
		default: /* case 0: */ break;
	}
	return hash;
}

unsigned int hash_sdbm(const char *key, int len)
{
	unsigned int hash = 0;
	int c;

	while (len--) {
		c = *key++;
		hash = c + (hash << 6) + (hash << 16) - hash;
	}

	return hash;
}

/* Small yet efficient CRC32 calculation loosely inspired from crc32b found
 * here : http://www.hackersdelight.org/hdcodetxt/crc.c.txt
 * The magic value represents the polynom with one bit per exponent. Much
 * faster table-based versions exist but are pointless for our usage here,
 * this hash already sustains gigabit speed which is far faster than what
 * we'd ever need. Better preserve the CPU's cache instead.
 */
unsigned int hash_crc32(const char *key, int len)
{
	unsigned int hash;
	int bit;

	hash = ~0;
	while (len--) {
		hash ^= *key++;
		for (bit = 0; bit < 8; bit++)
			hash = (hash >> 1) ^ ((hash & 1) ? 0xedb88320 : 0);
	}
	return ~hash;
}

/* CRC32c poly 0x11EDC6F41 (RFC4960, Appendix B [8].) */
static const uint32_t crctable[256] = {
  0x00000000L, 0xF26B8303L, 0xE13B70F7L, 0x1350F3F4L,
  0xC79A971FL, 0x35F1141CL, 0x26A1E7E8L, 0xD4CA64EBL,
  0x8AD958CFL, 0x78B2DBCCL, 0x6BE22838L, 0x9989AB3BL,
  0x4D43CFD0L, 0xBF284CD3L, 0xAC78BF27L, 0x5E133C24L,
  0x105EC76FL, 0xE235446CL, 0xF165B798L, 0x030E349BL,
  0xD7C45070L, 0x25AFD373L, 0x36FF2087L, 0xC494A384L,
  0x9A879FA0L, 0x68EC1CA3L, 0x7BBCEF57L, 0x89D76C54L,
  0x5D1D08BFL, 0xAF768BBCL, 0xBC267848L, 0x4E4DFB4BL,
  0x20BD8EDEL, 0xD2D60DDDL, 0xC186FE29L, 0x33ED7D2AL,
  0xE72719C1L, 0x154C9AC2L, 0x061C6936L, 0xF477EA35L,
  0xAA64D611L, 0x580F5512L, 0x4B5FA6E6L, 0xB93425E5L,
  0x6DFE410EL, 0x9F95C20DL, 0x8CC531F9L, 0x7EAEB2FAL,
  0x30E349B1L, 0xC288CAB2L, 0xD1D83946L, 0x23B3BA45L,
  0xF779DEAEL, 0x05125DADL, 0x1642AE59L, 0xE4292D5AL,
  0xBA3A117EL, 0x4851927DL, 0x5B016189L, 0xA96AE28AL,
  0x7DA08661L, 0x8FCB0562L, 0x9C9BF696L, 0x6EF07595L,
  0x417B1DBCL, 0xB3109EBFL, 0xA0406D4BL, 0x522BEE48L,
  0x86E18AA3L, 0x748A09A0L, 0x67DAFA54L, 0x95B17957L,
  0xCBA24573L, 0x39C9C670L, 0x2A993584L, 0xD8F2B687L,
  0x0C38D26CL, 0xFE53516FL, 0xED03A29BL, 0x1F682198L,
  0x5125DAD3L, 0xA34E59D0L, 0xB01EAA24L, 0x42752927L,
  0x96BF4DCCL, 0x64D4CECFL, 0x77843D3BL, 0x85EFBE38L,
  0xDBFC821CL, 0x2997011FL, 0x3AC7F2EBL, 0xC8AC71E8L,
  0x1C661503L, 0xEE0D9600L, 0xFD5D65F4L, 0x0F36E6F7L,
  0x61C69362L, 0x93AD1061L, 0x80FDE395L, 0x72966096L,
  0xA65C047DL, 0x5437877EL, 0x4767748AL, 0xB50CF789L,
  0xEB1FCBADL, 0x197448AEL, 0x0A24BB5AL, 0xF84F3859L,
  0x2C855CB2L, 0xDEEEDFB1L, 0xCDBE2C45L, 0x3FD5AF46L,
  0x7198540DL, 0x83F3D70EL, 0x90A324FAL, 0x62C8A7F9L,
  0xB602C312L, 0x44694011L, 0x5739B3E5L, 0xA55230E6L,
  0xFB410CC2L, 0x092A8FC1L, 0x1A7A7C35L, 0xE811FF36L,
  0x3CDB9BDDL, 0xCEB018DEL, 0xDDE0EB2AL, 0x2F8B6829L,
  0x82F63B78L, 0x709DB87BL, 0x63CD4B8FL, 0x91A6C88CL,
  0x456CAC67L, 0xB7072F64L, 0xA457DC90L, 0x563C5F93L,
  0x082F63B7L, 0xFA44E0B4L, 0xE9141340L, 0x1B7F9043L,
  0xCFB5F4A8L, 0x3DDE77ABL, 0x2E8E845FL, 0xDCE5075CL,
  0x92A8FC17L, 0x60C37F14L, 0x73938CE0L, 0x81F80FE3L,
  0x55326B08L, 0xA759E80BL, 0xB4091BFFL, 0x466298FCL,
  0x1871A4D8L, 0xEA1A27DBL, 0xF94AD42FL, 0x0B21572CL,
  0xDFEB33C7L, 0x2D80B0C4L, 0x3ED04330L, 0xCCBBC033L,
  0xA24BB5A6L, 0x502036A5L, 0x4370C551L, 0xB11B4652L,
  0x65D122B9L, 0x97BAA1BAL, 0x84EA524EL, 0x7681D14DL,
  0x2892ED69L, 0xDAF96E6AL, 0xC9A99D9EL, 0x3BC21E9DL,
  0xEF087A76L, 0x1D63F975L, 0x0E330A81L, 0xFC588982L,
  0xB21572C9L, 0x407EF1CAL, 0x532E023EL, 0xA145813DL,
  0x758FE5D6L, 0x87E466D5L, 0x94B49521L, 0x66DF1622L,
  0x38CC2A06L, 0xCAA7A905L, 0xD9F75AF1L, 0x2B9CD9F2L,
  0xFF56BD19L, 0x0D3D3E1AL, 0x1E6DCDEEL, 0xEC064EEDL,
  0xC38D26C4L, 0x31E6A5C7L, 0x22B65633L, 0xD0DDD530L,
  0x0417B1DBL, 0xF67C32D8L, 0xE52CC12CL, 0x1747422FL,
  0x49547E0BL, 0xBB3FFD08L, 0xA86F0EFCL, 0x5A048DFFL,
  0x8ECEE914L, 0x7CA56A17L, 0x6FF599E3L, 0x9D9E1AE0L,
  0xD3D3E1ABL, 0x21B862A8L, 0x32E8915CL, 0xC083125FL,
  0x144976B4L, 0xE622F5B7L, 0xF5720643L, 0x07198540L,
  0x590AB964L, 0xAB613A67L, 0xB831C993L, 0x4A5A4A90L,
  0x9E902E7BL, 0x6CFBAD78L, 0x7FAB5E8CL, 0x8DC0DD8FL,
  0xE330A81AL, 0x115B2B19L, 0x020BD8EDL, 0xF0605BEEL,
  0x24AA3F05L, 0xD6C1BC06L, 0xC5914FF2L, 0x37FACCF1L,
  0x69E9F0D5L, 0x9B8273D6L, 0x88D28022L, 0x7AB90321L,
  0xAE7367CAL, 0x5C18E4C9L, 0x4F48173DL, 0xBD23943EL,
  0xF36E6F75L, 0x0105EC76L, 0x12551F82L, 0xE03E9C81L,
  0x34F4F86AL, 0xC69F7B69L, 0xD5CF889DL, 0x27A40B9EL,
  0x79B737BAL, 0x8BDCB4B9L, 0x988C474DL, 0x6AE7C44EL,
  0xBE2DA0A5L, 0x4C4623A6L, 0x5F16D052L, 0xAD7D5351L
};

uint32_t hash_crc32c(const char *buf, int len)
{
	uint32_t crc = 0xffffffff;
	while (len-- > 0) {
		crc = (crc >> 8) ^ crctable[(crc ^ (*buf++)) & 0xff];
	}
	return (crc ^ 0xffffffff);
}