dice.c

#include "dice.h"
#include <stdint.h>
#include <curses.h>


/* - THE SAUCE - */
static uint32_t x = 0;                   // default PRNG seed value

// You can play with these
typedef uint32_t wheel32;
static wheel32 c_wheel = 19937;         // must be a circular prime
static wheel32 a_wheel = 11939;         // must be a circular prime
static const int digits_in_a_wheel = 5;     // used in shake_dice()
static const int digits_in_c_wheel = 5;     // used in shake_dice()
static const uint32_t c_multiplier = 2401;  // any odd number

// But don't alter these formulas... unless you really want to
static const uint32_t max_16bit_number = 65520;
uint32_t a(void) { return (4 * a_wheel + 1); }
uint32_t c(void) { return (c_multiplier * c_wheel); }

uint32_t new_16bits(void) {
    x = a() * x + c();
    if ((x >> 16) > max_16bit_number)
        new_16bits();
    return (x >> 16);
}

void rotate_wheel(wheel32 *wheel) {
    *wheel = *wheel / 10 + 10000 * (*wheel % 10);
    return;
}


/* - THE IMPLEMENTATION - */
void seed_dice(int seed) {
    x = (uint32_t)seed;
    return;
}

void shake_dice(int num) {
    int a_rolls = roll(num, d4) % digits_in_a_wheel;
    int c_rolls = roll(num, d4) % digits_in_c_wheel;
    for ( ; a_rolls > 0; a_rolls--) rotate_wheel(&a_wheel);
    for ( ; c_rolls > 0; c_rolls--) rotate_wheel(&c_wheel);
    return;
}

int flip_coin(void) {
    return (int)new_16bits() % 2;
}

int flip_coins(int num) {
    int value = 0;
    for (int i = 0; i < num; i++) value += flip_coin();
    return value;
}

int roll(int num, dice_type dice) {
    int value = 0;
    for (int i = 0; i < num; i++)
        value += (int)new_16bits() % (int)dice;
        if (dice != d10) value++; // d10's go from 0 -> 9
    return value;
}

int roll_percentile(void) {
    int value = roll(1, d10) * 10 + roll(1, d10);
    return (value ? value : 100); // 00 + 0 is 100 for percentile rolls
}

/*void test_wheels(void) {
    for (int i = 0; i < 6; i++) {
        rotate_wheel(&a_wheel);
        rotate_wheel(&c_wheel);
        printw("%du : %du\n", a_wheel, c_wheel);
        getch();
    }
}*/