github.com/pidato/unsafe@v0.1.4/memory/hash/wyhash.h

// This is free and unencumbered software released into the public domain under The Unlicense (http://unlicense.org/)
// main repo: https://github.com/wangyi-fudan/wyhash
// author: 王一 Wang Yi <godspeed_china@yeah.net>
// contributors: Reini Urban, Dietrich Epp, Joshua Haberman, Tommy Ettinger, Daniel Lemire, Otmar Ertl, cocowalla, leo-yuriev, Diego Barrios Romero, paulie-g, dumblob, Yann Collet, ivte-ms, hyb, James Z.M. Gao, easyaspi314 (Devin), TheOneric

/* quick example:
   string s="fjsakfdsjkf";
   uint64_t hash=wyhash(s.c_str(), s.size(), 0, _wyp);
*/

#ifndef wyhash_final_version_3
#define wyhash_final_version_3

#ifndef WYHASH_CONDOM
//protections that produce different results:
//1: normal valid behavior
//2: extra protection against entropy loss (probability=2^-63), aka. "blind multiplication"
#define WYHASH_CONDOM 1
#endif

#ifndef WYHASH_32BIT_MUM
//0: normal version, slow on 32 bit systems
//1: faster on 32 bit systems but produces different results, incompatible with wy2u0k function
#define WYHASH_32BIT_MUM 0
#endif

//includes
#include <stdint.h>
#include <string.h>
#if defined(_MSC_VER) && defined(_M_X64)
  #include <intrin.h>
  #pragma intrinsic(_umul128)
#endif

//likely and unlikely macros
#if defined(__GNUC__) || defined(__INTEL_COMPILER) || defined(__clang__)
  #define _likely_(x)  __builtin_expect(x,1)
  #define _unlikely_(x)  __builtin_expect(x,0)
#else
  #define _likely_(x) (x)
  #define _unlikely_(x) (x)
#endif

//128bit multiply function
static inline uint64_t _wyrot(uint64_t x) { return (x>>32)|(x<<32); }
static inline void _wymum(uint64_t *A, uint64_t *B){
#if(WYHASH_32BIT_MUM)
  uint64_t hh=(*A>>32)*(*B>>32), hl=(*A>>32)*(uint32_t)*B, lh=(uint32_t)*A*(*B>>32), ll=(uint64_t)(uint32_t)*A*(uint32_t)*B;
  #if(WYHASH_CONDOM>1)
  *A^=_wyrot(hl)^hh; *B^=_wyrot(lh)^ll;
  #else
  *A=_wyrot(hl)^hh; *B=_wyrot(lh)^ll;
  #endif
#elif defined(__SIZEOF_INT128__)
  __uint128_t r=*A; r*=*B;
  #if(WYHASH_CONDOM>1)
  *A^=(uint64_t)r; *B^=(uint64_t)(r>>64);
  #else
  *A=(uint64_t)r; *B=(uint64_t)(r>>64);
  #endif
#elif defined(_MSC_VER) && defined(_M_X64)
  #if(WYHASH_CONDOM>1)
  uint64_t  a,  b;
  a=_umul128(*A,*B,&b);
  *A^=a;  *B^=b;
  #else
  *A=_umul128(*A,*B,B);
  #endif
#else
  uint64_t ha=*A>>32, hb=*B>>32, la=(uint32_t)*A, lb=(uint32_t)*B, hi, lo;
  uint64_t rh=ha*hb, rm0=ha*lb, rm1=hb*la, rl=la*lb, t=rl+(rm0<<32), c=t<rl;
  lo=t+(rm1<<32); c+=lo<t; hi=rh+(rm0>>32)+(rm1>>32)+c;
  #if(WYHASH_CONDOM>1)
  *A^=lo;  *B^=hi;
  #else
  *A=lo;  *B=hi;
  #endif
#endif
}

//multiply and xor mix function, aka MUM
static inline uint64_t _wymix(uint64_t A, uint64_t B){ _wymum(&A,&B); return A^B; }

//endian macros
#ifndef WYHASH_LITTLE_ENDIAN
  #if defined(_WIN32) || defined(__LITTLE_ENDIAN__) || (defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
    #define WYHASH_LITTLE_ENDIAN 1
  #elif defined(__BIG_ENDIAN__) || (defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
    #define WYHASH_LITTLE_ENDIAN 0
  #else
    #warning could not determine endianness! Falling back to little endian.
    #define WYHASH_LITTLE_ENDIAN 1
  #endif
#endif

//read functions
#if (WYHASH_LITTLE_ENDIAN)
static inline uint64_t _wyr8(const uint8_t *p) { uint64_t v; memcpy(&v, p, 8); return v;}
static inline uint64_t _wyr4(const uint8_t *p) { uint32_t v; memcpy(&v, p, 4); return v;}
#elif defined(__GNUC__) || defined(__INTEL_COMPILER) || defined(__clang__)
static inline uint64_t _wyr8(const uint8_t *p) { uint64_t v; memcpy(&v, p, 8); return __builtin_bswap64(v);}
static inline uint64_t _wyr4(const uint8_t *p) { uint32_t v; memcpy(&v, p, 4); return __builtin_bswap32(v);}
#elif defined(_MSC_VER)
static inline uint64_t _wyr8(const uint8_t *p) { uint64_t v; memcpy(&v, p, 8); return _byteswap_uint64(v);}
static inline uint64_t _wyr4(const uint8_t *p) { uint32_t v; memcpy(&v, p, 4); return _byteswap_ulong(v);}
#else
static inline uint64_t _wyr8(const uint8_t *p) {
  uint64_t v; memcpy(&v, p, 8);
  return (((v >> 56) & 0xff)| ((v >> 40) & 0xff00)| ((v >> 24) & 0xff0000)| ((v >>  8) & 0xff000000)| ((v <<  8) & 0xff00000000)| ((v << 24) & 0xff0000000000)| ((v << 40) & 0xff000000000000)| ((v << 56) & 0xff00000000000000));
}
static inline uint64_t _wyr4(const uint8_t *p) {
  uint32_t v; memcpy(&v, p, 4);
  return (((v >> 24) & 0xff)| ((v >>  8) & 0xff00)| ((v <<  8) & 0xff0000)| ((v << 24) & 0xff000000));
}
#endif
static inline uint64_t _wyr3(const uint8_t *p, size_t k) { return (((uint64_t)p[0])<<16)|(((uint64_t)p[k>>1])<<8)|p[k-1];}
//wyhash main function
static inline uint64_t wyhash(const void *key, size_t len, uint64_t seed, const uint64_t *secret){
  const uint8_t *p=(const uint8_t *)key; seed^=*secret;	uint64_t	a,	b;
  if(_likely_(len<=16)){
    if(_likely_(len>=4)){ a=(_wyr4(p)<<32)|_wyr4(p+((len>>3)<<2)); b=(_wyr4(p+len-4)<<32)|_wyr4(p+len-4-((len>>3)<<2)); }
    else if(_likely_(len>0)){ a=_wyr3(p,len); b=0;}
    else a=b=0;
  }
  else{
    size_t i=len;
    if(_unlikely_(i>48)){
      uint64_t see1=seed, see2=seed;
      do{
        seed=_wymix(_wyr8(p)^secret[1],_wyr8(p+8)^seed);
        see1=_wymix(_wyr8(p+16)^secret[2],_wyr8(p+24)^see1);
        see2=_wymix(_wyr8(p+32)^secret[3],_wyr8(p+40)^see2);
        p+=48; i-=48;
      }while(_likely_(i>48));
      seed^=see1^see2;
    }
    while(_unlikely_(i>16)){  seed=_wymix(_wyr8(p)^secret[1],_wyr8(p+8)^seed);  i-=16; p+=16;  }
    a=_wyr8(p+i-16);  b=_wyr8(p+i-8);
  }
  return _wymix(secret[1]^len,_wymix(a^secret[1],b^seed));
}

//the default secret parameters
static const uint64_t _wyp[4] = {0xa0761d6478bd642full, 0xe7037ed1a0b428dbull, 0x8ebc6af09c88c6e3ull, 0x589965cc75374cc3ull};

//a useful 64bit-64bit mix function to produce deterministic pseudo random numbers that can pass BigCrush and PractRand
static inline uint64_t wyhash64(uint64_t A, uint64_t B){ A^=0xa0761d6478bd642full; B^=0xe7037ed1a0b428dbull; _wymum(&A,&B); return _wymix(A^0xa0761d6478bd642full,B^0xe7037ed1a0b428dbull);}

//The wyrand PRNG that pass BigCrush and PractRand
static inline uint64_t wyrand(uint64_t *seed){ *seed+=0xa0761d6478bd642full; return _wymix(*seed,*seed^0xe7037ed1a0b428dbull);}

//convert any 64 bit pseudo random numbers to uniform distribution [0,1). It can be combined with wyrand, wyhash64 or wyhash.
static inline double wy2u01(uint64_t r){ const double _wynorm=1.0/(1ull<<52); return (r>>12)*_wynorm;}

//convert any 64 bit pseudo random numbers to APPROXIMATE Gaussian distribution. It can be combined with wyrand, wyhash64 or wyhash.
static inline double wy2gau(uint64_t r){ const double _wynorm=1.0/(1ull<<20); return ((r&0x1fffff)+((r>>21)&0x1fffff)+((r>>42)&0x1fffff))*_wynorm-3.0;}

#if(!WYHASH_32BIT_MUM)
//fast range integer random number generation on [0,k) credit to Daniel Lemire. May not work when WYHASH_32BIT_MUM=1. It can be combined with wyrand, wyhash64 or wyhash.
static inline uint64_t wy2u0k(uint64_t r, uint64_t k){ _wymum(&r,&k); return k; }
#endif

//make your own secret
static inline void make_secret(uint64_t seed, uint64_t *secret){
  uint8_t c[] = {15, 23, 27, 29, 30, 39, 43, 45, 46, 51, 53, 54, 57, 58, 60, 71, 75, 77, 78, 83, 85, 86, 89, 90, 92, 99, 101, 102, 105, 106, 108, 113, 114, 116, 120, 135, 139, 141, 142, 147, 149, 150, 153, 154, 156, 163, 165, 166, 169, 170, 172, 177, 178, 180, 184, 195, 197, 198, 201, 202, 204, 209, 210, 212, 216, 225, 226, 228, 232, 240 };
  for(size_t i=0;i<4;i++){
    uint8_t ok;
    do{
      ok=1; secret[i]=0;
      for(size_t j=0;j<64;j+=8) secret[i]|=((uint64_t)c[wyrand(&seed)%sizeof(c)])<<j;
      if(secret[i]%2==0){ ok=0; continue; }
      for(size_t j=0;j<i;j++) {
#if defined(__GNUC__) || defined(__INTEL_COMPILER) || defined(__clang__)
        if(__builtin_popcountll(secret[j]^secret[i])!=32){ ok=0; break; }
#elif defined(_MSC_VER) && defined(_M_X64)
        if(_mm_popcnt_u64(secret[j]^secret[i])!=32){ ok=0; break; }
#else
        //manual popcount
        uint64_t x = secret[j]^secret[i];
        x -= (x >> 1) & 0x5555555555555555;
        x = (x & 0x3333333333333333) + ((x >> 2) & 0x3333333333333333);
        x = (x + (x >> 4)) & 0x0f0f0f0f0f0f0f0f;
        x = (x * 0x0101010101010101) >> 56;
        if(x!=32){ ok=0; break; }
#endif
      }
    }while(!ok);
  }
}

/*  This is world's fastest hash map: 2x faster than bytell_hash_map.
    It does not store the keys, but only the hash/signature of keys.
    First we use pos=hash1(key) to approximately locate the bucket.
    Then we search signature=hash2(key) from pos linearly.
    If we find a bucket with matched signature we report the bucket
    Or if we meet a bucket whose signature=0, we report a new position to insert
    The signature collision probability is very low as we usually searched N~10 buckets.
    By combining hash1 and hash2, we acturally have 128 bit anti-collision strength.
    hash1 and hash2 can be the same function, resulting lower collision resistance but faster.
    The signature is 64 bit, but can be modified to 32 bit if necessary for save space.
    The above two can be activated by define WYHASHMAP_WEAK_SMALL_FAST
    simple examples:
    const	size_t	size=213432;
    vector<wyhashmap_t>	idx(size);	//	allocate the index of fixed size. idx MUST be zeroed.
    vector<value_class>	value(size);	//	we only care about the index, user should maintain his own value vectors.
    string  key="dhskfhdsj"	//	the object to be inserted into idx
    size_t	pos=wyhashmap(idx.data(), idx.size(), key.c_str(), key.size(), 1);	//	get the position and insert
    if(pos<size)	value[pos]++;	//	we process the vallue
    else	cerr<<"map is full\n";
    pos=wyhashmap(idx.data(), idx.size(), key.c_str(), key.size(), 0);	// just lookup by setting insert=0
    if(pos<size)	value[pos]++;	//	we process the vallue
    else	cerr<<"the key does not exist\n";
*/
/*
#ifdef	WYHASHMAP_WEAK_SMALL_FAST	// for small hashmaps whose size < 2^24 and acceptable collision
typedef	uint32_t	wyhashmap_t;
#else
typedef	uint64_t	wyhashmap_t;
#endif
static	inline	size_t	wyhashmap(wyhashmap_t	*idx,	size_t	idx_size,	const	void *key, size_t	key_size,	uint8_t	insert, uint64_t *secret){
	size_t	i=1;	uint64_t	h2;	wyhashmap_t	sig;
	do{	sig=h2=wyhash(key,key_size,i,secret);	i++;	}while(_unlikely_(!sig));
#ifdef	WYHASHMAP_WEAK_SMALL_FAST
	size_t	i0=wy2u0k(h2,idx_size);
#else
	size_t	i0=wy2u0k(wyhash(key,key_size,0,secret),idx_size);
#endif
	for(i=i0;	i<idx_size&&idx[i]&&idx[i]!=sig;	i++);
	if(_unlikely_(i==idx_size)){
		for(i=0;	i<i0&&idx[i]&&idx[i]!=sig;  i++);
		if(i==i0)	return	idx_size;
	}
	if(!idx[i]){
		if(insert)	idx[i]=sig;
		else	return	idx_size;
	}
	return	i;
}
*/
#endif

/* The Unlicense
This is free and unencumbered software released into the public domain.
Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.
In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.
For more information, please refer to <http://unlicense.org/>
*/