Function mul_64_64

numpy/core/src/common/npy_extint128.h:90–126

Long integer multiply */

/* Long integer multiply */
static inline npy_extint128_t
mul_64_64(npy_int64 a, npy_int64 b)
{
    npy_extint128_t x, y, z;
    npy_uint64 x1, x2, y1, y2, r1, r2, prev;

    x = to_128(a);
    y = to_128(b);

    x1 = x.lo & 0xffffffff;
    x2 = x.lo >> 32;

    y1 = y.lo & 0xffffffff;
    y2 = y.lo >> 32;

    r1 = x1*y2;
    r2 = x2*y1;

    z.sign = x.sign * y.sign;
    z.hi = x2*y2 + (r1 >> 32) + (r2 >> 32);
    z.lo = x1*y1;

    /* Add with carry */
    prev = z.lo;
    z.lo += (r1 << 32);
    if (z.lo < prev) {
        ++z.hi;
    }

    prev = z.lo;
    z.lo += (r2 << 32);
    if (z.lo < prev) {
        ++z.hi;
    }

    return z;
}


/* Long integer add */