[LAD] 64 bit tempo-based time stamp

[David Robillard]

Hi all, seeking opinions:

I have to choose a way to represent beat-based tempo time in 64 bits.
Uses are many, but the main one is event time stamps for plugins.

Requirements:
 * No odd data sizes (for performance / programmer ease)
 * High precision (ideally close to sample accurate for most tempos)
 * Fits in the same space as two uint32_t's

Questions:
 * Is "bar" needed?
 * Use floating point?  Rounding errors an issue?

Options:

/* A (moderate range, ultra precise) */
struct {
    uint16_t bar;
    uint16_t beat;
    uint32_t tick;
};

/* B (high range, moderate precision) */
struct {
    uint32_t bar;
    uint16_t beat;
    uint16_t tick;
};

/* C (high range, good precision?) */
struct {
    uint32_t bar
    float    beat;
};

/* D (high range/precision, but no bar) */
double beat;

I havn't run the math on precision yet, but I am leaning towards C.  I
actually hadn't considered mixing int and float before writing this
email, but it seems the best trade-off, and working with float is
certainly more pleasant than fixed point.

Thoughts?

-dr