int128.h

#ifndef INT128_H
#define INT128_H

typedef struct Int128 Int128;

struct Int128 {
    uint64_t lo;
    int64_t hi;
};

static inline Int128 int128_make64(uint64_t a)
{
    return (Int128) { a, 0 };
}

static inline uint64_t int128_get64(Int128 a)
{
    assert(!a.hi);
    return a.lo;
}

static inline Int128 int128_zero(void)
{
    return int128_make64(0);
}

static inline Int128 int128_one(void)
{
    return int128_make64(1);
}

static inline Int128 int128_2_64(void)
{
    return (Int128) { 0, 1 };
}

static inline Int128 int128_add(Int128 a, Int128 b)
{
    Int128 r = { a.lo + b.lo, a.hi + b.hi };
    r.hi += (r.lo < a.lo) || (r.lo < b.lo);
    return r;
}

static inline Int128 int128_neg(Int128 a)
{
    a.lo = ~a.lo;
    a.hi = ~a.hi;
    return int128_add(a, int128_one());
}

static inline Int128 int128_sub(Int128 a, Int128 b)
{
    return int128_add(a, int128_neg(b));
}

static inline bool int128_nonneg(Int128 a)
{
    return a.hi >= 0;
}

static inline bool int128_eq(Int128 a, Int128 b)
{
    return a.lo == b.lo && a.hi == b.hi;
}

static inline bool int128_ne(Int128 a, Int128 b)
{
    return !int128_eq(a, b);
}

static inline bool int128_ge(Int128 a, Int128 b)
{
    return int128_nonneg(int128_sub(a, b));
}

static inline bool int128_lt(Int128 a, Int128 b)
{
    return !int128_ge(a, b);
}

static inline bool int128_le(Int128 a, Int128 b)
{
    return int128_ge(b, a);
}

static inline bool int128_gt(Int128 a, Int128 b)
{
    return !int128_le(a, b);
}

static inline bool int128_nz(Int128 a)
{
    return a.lo || a.hi;
}

static inline Int128 int128_min(Int128 a, Int128 b)
{
    return int128_le(a, b) ? a : b;
}

static inline Int128 int128_max(Int128 a, Int128 b)
{
    return int128_ge(a, b) ? a : b;
}

static inline void int128_addto(Int128 *a, Int128 b)
{
    *a = int128_add(*a, b);
}

static inline void int128_subfrom(Int128 *a, Int128 b)
{
    *a = int128_sub(*a, b);
}

#endif