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dis-bench / src /php /php-src /ext /random /gammasection.c
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/*
+----------------------------------------------------------------------+
| Copyright (c) The PHP Group |
+----------------------------------------------------------------------+
| This source file is subject to version 3.01 of the PHP license, |
| that is bundled with this package in the file LICENSE, and is |
| available through the world-wide-web at the following url: |
| https://www.php.net/license/3_01.txt |
| If you did not receive a copy of the PHP license and are unable to |
| obtain it through the world-wide-web, please send a note to |
| license@php.net so we can mail you a copy immediately. |
+----------------------------------------------------------------------+
| Authors: Tim Düsterhus <timwolla@php.net> |
| |
| Based on code from: Frédéric Goualard |
| Corrected to handled appropriately random integers larger than 2^53 |
| converted to double precision floats, and to avoid overflows for |
| large gammas. |
+----------------------------------------------------------------------+
*/
#ifdef HAVE_CONFIG_H
# include "config.h"
#endif
#include "php.h"
#include "php_random.h"
#include <math.h>
/* This file implements the γ-section algorithm as published in:
*
* Drawing Random Floating-Point Numbers from an Interval. Frédéric
* Goualard, ACM Trans. Model. Comput. Simul., 32:3, 2022.
* https://doi.org/10.1145/3503512
*/
static double gamma_low(double x)
{
return x - nextafter(x, -DBL_MAX);
}
static double gamma_high(double x)
{
return nextafter(x, DBL_MAX) - x;
}
static double gamma_max(double x, double y)
{
return (fabs(x) > fabs(y)) ? gamma_high(x) : gamma_low(y);
}
static void splitint64(uint64_t v, double *vhi, double *vlo)
{
*vhi = v >> 2;
*vlo = v & UINT64_C(0x3);
}
static uint64_t ceilint(double a, double b, double g)
{
double s = b / g - a / g;
double e;
if (fabs(a) <= fabs(b)) {
e = -a / g - (s - b / g);
} else {
e = b / g - (s + a / g);
}
double si = ceil(s);
return (s != si) ? (uint64_t)si : (uint64_t)si + (e > 0);
}
PHPAPI double php_random_gammasection_closed_open(php_random_algo_with_state engine, double min, double max)
{
double g = gamma_max(min, max);
uint64_t hi = ceilint(min, max, g);
if (UNEXPECTED(max <= min || hi < 1)) {
return NAN;
}
uint64_t k = 1 + php_random_range64(engine, hi - 1); /* [1, hi] */
if (fabs(min) <= fabs(max)) {
if (k == hi) {
return min;
} else {
double k_hi, k_lo;
splitint64(k, &k_hi, &k_lo);
return 0x1p+2 * (max * 0x1p-2 - k_hi * g) - k_lo * g;
}
} else {
double k_hi, k_lo;
splitint64(k - 1, &k_hi, &k_lo);
return 0x1p+2 * (min * 0x1p-2 + k_hi * g) + k_lo * g;
}
}
PHPAPI double php_random_gammasection_closed_closed(php_random_algo_with_state engine, double min, double max)
{
double g = gamma_max(min, max);
uint64_t hi = ceilint(min, max, g);
if (UNEXPECTED(max < min)) {
return NAN;
}
uint64_t k = php_random_range64(engine, hi); /* [0, hi] */
if (fabs(min) <= fabs(max)) {
if (k == hi) {
return min;
} else {
double k_hi, k_lo;
splitint64(k, &k_hi, &k_lo);
return 0x1p+2 * (max * 0x1p-2 - k_hi * g) - k_lo * g;
}
} else {
if (k == hi) {
return max;
} else {
double k_hi, k_lo;
splitint64(k, &k_hi, &k_lo);
return 0x1p+2 * (min * 0x1p-2 + k_hi * g) + k_lo * g;
}
}
}
PHPAPI double php_random_gammasection_open_closed(php_random_algo_with_state engine, double min, double max)
{
double g = gamma_max(min, max);
uint64_t hi = ceilint(min, max, g);
if (UNEXPECTED(max <= min || hi < 1)) {
return NAN;
}
uint64_t k = php_random_range64(engine, hi - 1); /* [0, hi - 1] */
if (fabs(min) <= fabs(max)) {
double k_hi, k_lo;
splitint64(k, &k_hi, &k_lo);
return 0x1p+2 * (max * 0x1p-2 - k_hi * g) - k_lo * g;
} else {
if (k == (hi - 1)) {
return max;
} else {
double k_hi, k_lo;
splitint64(k + 1, &k_hi, &k_lo);
return 0x1p+2 * (min * 0x1p-2 + k_hi * g) + k_lo * g;
}
}
}
PHPAPI double php_random_gammasection_open_open(php_random_algo_with_state engine, double min, double max)
{
double g = gamma_max(min, max);
uint64_t hi = ceilint(min, max, g);
if (UNEXPECTED(max <= min || hi < 2)) {
return NAN;
}
uint64_t k = 1 + php_random_range64(engine, hi - 2); /* [1, hi - 1] */
if (fabs(min) <= fabs(max)) {
double k_hi, k_lo;
splitint64(k, &k_hi, &k_lo);
return 0x1p+2 * (max * 0x1p-2 - k_hi * g) - k_lo * g;
} else {
double k_hi, k_lo;
splitint64(k, &k_hi, &k_lo);
return 0x1p+2 * (min * 0x1p-2 + k_hi * g) + k_lo * g;
}
}