/* uses https://www.bellard.org/libbf/
 * gcc -o prog prog.c libbf.o cutils.o
 */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#include "libbf.h"

static bf_context_t bf_ctx;

static void *my_bf_realloc(void *opaque, void *ptr, size_t size)
{
        return realloc(ptr, size);
}

static void strrev(char *s)
{
        int l = 0, r = strlen(s) - 1;
        while (l < r) {
                char c = s[r];
                s[r] = s[l];
                s[l] = c;
                l++;
                r--;
        }
}

static char *base36encode(const bf_t *n)
{
        static char s[8192];
        const char *t = "0123456789abcdefghijklmnopqrstuvwxyz";
        bf_t f, x, y, z, c36;
        int off = 0, i;

        bf_init(&bf_ctx, &f);
        bf_init(&bf_ctx, &x);
        bf_init(&bf_ctx, &y);
        bf_init(&bf_ctx, &z);
        bf_init(&bf_ctx, &c36);
        bf_set_ui(&c36, 36);

        bf_set(&x, n);
        bf_rint(&x, BF_RNDZ);
        bf_sub(&f, n, &x, 128, 0);

        while (!bf_is_zero(&x)) {
                bf_divrem(&y, &z, &x, &c36, 128, 0, BF_RNDZ);
                bf_get_int32(&i, &z, 0);
                s[off++] = t[i];
                bf_set(&x, &y);
        }
        s[off] = 0;
        strrev(s);
        s[off++] = '.';

        for (int j = 0; j < 20; ++j) {
                bf_mul(&x, &f, &c36, 128, 0);
                bf_set(&y, &x);
                bf_rint(&y, BF_RNDZ);
                bf_get_int32(&i, &y, 0);
                s[off++] = t[i];
                bf_sub(&f, &x, &y, 128, 0);
        }
        s[off] = 0;
        return s;
}

int main()
{
        bf_t pi, r, x, y, z, m, d, l, a, b, c, e, f, g;
        int status;
        char *s;
        uint64_t u, v;

        bf_context_init(&bf_ctx, my_bf_realloc, NULL);
        bf_init(&bf_ctx, &pi);
        bf_init(&bf_ctx, &r);
        bf_init(&bf_ctx, &x);
        bf_init(&bf_ctx, &y);
        bf_init(&bf_ctx, &z);
        bf_init(&bf_ctx, &m);
        bf_init(&bf_ctx, &d);
        bf_init(&bf_ctx, &l);
        bf_init(&bf_ctx, &a);
        bf_init(&bf_ctx, &b);
        bf_init(&bf_ctx, &c);
        bf_init(&bf_ctx, &e);
        bf_init(&bf_ctx, &f);
        bf_init(&bf_ctx, &g);
        bf_const_pi(&pi, 256, 0);
        bf_atof(&l, "0.00000001", NULL, 10, 128, BF_RNDZ);
        bf_atof(&r, "29053366.650397708275965", NULL, 10, 128, BF_RNDZ);

        s = bf_ftoa(NULL, &r, 10, 128, BF_RNDZ);
        printf("%s\n", s);
        s = base36encode(&r);
        printf("%s\n", s);

        bf_atan(&x, &r, 256, 0);
        s = bf_ftoa(NULL, &x, 10, 128, BF_RNDZ);
        printf("%s\n", s);

        bf_set_ui(&e, 1);
        bf_set_ui(&f, 1);
        u = 0;
        while (1) {
                bf_add(&g, &e, &f, 128, 0);
                bf_set(&e, &g);
                if (++u == 10000000) {
                        s = bf_ftoa(NULL, &e, 10, 128, BF_RNDZ);
                        printf("%s\n", s);
                        u = 0;
                }

                bf_mul(&y, &pi, &e, 128, 0);
                bf_add(&z, &x, &y, 128, 0);

                bf_set(&r, &z);
                bf_rint(&r, BF_RNDZ);
                bf_sub(&d, &z, &r, 128, 0);

                if (bf_cmp_lt(&d, &l)) {
                        s = bf_ftoa(NULL, &e, 10, 128, BF_RNDZ);
                        printf("u=%s\n", s);
                        s = bf_ftoa(NULL, &z, 10, 128, BF_RNDZ);
                        printf("z=%s\n", s);
                        s = bf_ftoa(NULL, &r, 10, 128, BF_RNDZ);
                        printf("r=%s\n", s);
                        bf_tan(&y, &r, 256, 0);
                        s = bf_ftoa(NULL, &y, 10, 128, BF_RNDZ);
                        printf("y=%s\n", s);
                        s = base36encode(&y);
                        printf("%s\n", s);
                        if (!strncmp(s, "happy.newyear", 13))
                                return 0;
                }
        }
}