/* Borland Win16 random-number support reconstructed from Code5. */

#include "tdkpin_random.h"

enum { BORLAND_RANDOM_MULTIPLIER = 0x08088405u };

uint32_t borland_next_random(void)
{
    g_borland_random_seed =
        g_borland_random_seed * BORLAND_RANDOM_MULTIPLIER + 1u;
    return g_borland_random_seed;
}

uint16_t borland_random_below(uint16_t upper_bound)
{
    uint32_t random = borland_next_random();
    return (uint16_t)(((uint64_t)random * upper_bound) >> 32);
}

BorlandReal48 borland_random_real48_registers(void)
{
    uint32_t random = borland_next_random();
    if (random == 0) {
        return (BorlandReal48){{0, 0, 0, 0, 0, 0}};
    }
    uint8_t exponent = 0x80;
    while ((random & 0x80000000u) == 0) {
        random <<= 1;
        exponent--;
    }
    random &= 0x7fffffffu;
    return (BorlandReal48){{
        exponent,
        0,
        (uint8_t)random,
        (uint8_t)(random >> 8),
        (uint8_t)(random >> 16),
        (uint8_t)(random >> 24),
    }};
}

int8_t borland_random_exponent(void)
{
    return (int8_t)borland_random_real48_registers().bytes[0];
}

/*
 * 1020:14de — x87 Random: reinterpret the signed FILD of RandSeed as unsigned
 * by adding exactly 2^31, then FSCALE by -32. Binary64 represents every
 * uint32_t/2^32 result exactly, so this host spelling loses no target bits.
 */
double borland_random_unit_interval(void)
{
    uint32_t random = borland_next_random();
    return (double)random / 4294967296.0;
}

void borland_seed_random_from_dos_time(void)
{
    g_borland_random_seed = win16_dos_time_words();
}