femtolisp/llt/hashing.c

133 lines
2.7 KiB
C

/*
Hashing and random numbers
*/
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include "ieee754.h"
#include "dtypes.h"
#include "utils.h"
#include "hashing.h"
#include "timefuncs.h"
uint_t nextipow2(uint_t i)
{
if (i==0) return 1;
if ((i&(i-1))==0) return i;
if (i&TOP_BIT) return TOP_BIT;
// repeatedly clear bottom bit
while (i&(i-1))
i = i&(i-1);
return i<<1;
}
u_int32_t int32hash(u_int32_t a)
{
a = (a+0x7ed55d16) + (a<<12);
a = (a^0xc761c23c) ^ (a>>19);
a = (a+0x165667b1) + (a<<5);
a = (a+0xd3a2646c) ^ (a<<9);
a = (a+0xfd7046c5) + (a<<3);
a = (a^0xb55a4f09) ^ (a>>16);
return a;
}
u_int64_t int64hash(u_int64_t key)
{
key = (~key) + (key << 21); // key = (key << 21) - key - 1;
key = key ^ (key >> 24);
key = (key + (key << 3)) + (key << 8); // key * 265
key = key ^ (key >> 14);
key = (key + (key << 2)) + (key << 4); // key * 21
key = key ^ (key >> 28);
key = key + (key << 31);
return key;
}
u_int32_t int64to32hash(u_int64_t key)
{
key = (~key) + (key << 18); // key = (key << 18) - key - 1;
key = key ^ (key >> 31);
key = key * 21; // key = (key + (key << 2)) + (key << 4);
key = key ^ (key >> 11);
key = key + (key << 6);
key = key ^ (key >> 22);
return (u_int32_t)key;
}
#include "lookup3.c"
u_int64_t memhash(char* buf, size_t n)
{
u_int32_t c=0xcafe8881, b=0x4d6a087c;
hashlittle2(buf, n, &c, &b);
return (u_int64_t)c | (((u_int64_t)b)<<32);
}
#include "mt19937ar.c"
double rand_double()
{
union ieee754_double d;
d.ieee.mantissa0 = random();
d.ieee.mantissa1 = random();
d.ieee.negative = 0;
d.ieee.exponent = IEEE754_DOUBLE_BIAS + 0; /* 2^0 */
return d.d - 1.0;
}
float rand_float()
{
union ieee754_float f;
f.ieee.mantissa = random();
f.ieee.negative = 0;
f.ieee.exponent = IEEE754_FLOAT_BIAS + 0; /* 2^0 */
return f.f - 1.0;
}
double randn()
{
double s, vre, vim, ure, uim;
static double next = -42;
if (next != -42) {
s = next;
next = -42;
return s;
}
do {
ure = rand_double();
uim = rand_double();
vre = 2*ure - 1;
vim = 2*uim - 1;
s = vre*vre + vim*vim;
} while (s >= 1);
s = sqrt(-2*log(s)/s);
next = s * vre;
return s * vim;
}
void randomize()
{
u_int64_t tm = i64time();
init_by_array((unsigned long*)&tm, 2);
}
void llt_init()
{
/*
I used this function to guess good values based on epsilon:
tol(eps) = exp(ln(eps)*-.2334012088721472)*eps
I derived the constant by hallucinating freely.
*/
dbl_tolerance(1e-12);
flt_tolerance(5e-6);
randomize();
}