#include <string.h> /* size_t */
#include <limb/int.h>
#include "rabin-tables.h"

#define BREAKMARK_VALUE 0x78

size_t
nextsplit(size_t min, size_t avg, const void *data, size_t dlen)
{
    if (dlen <= min) return dlen;
    u64 sml_mask = (1 << (msb64(avg * 2) - 1)) - 1;
    u64 lrg_mask = (1 << (msb64(avg / 2) - 1)) - 1;
    u64 fp = 0;
    int i = min, wpos = -1;

    const u8 *sce = data;
    u8 window[RABIN_WINDOW_SIZE] = { 0 };

    while (i < dlen) {
        u8 om;
        u64 x;
        if (++wpos >= sizeof(window))
            wpos = 0;
        om = window[wpos];
        window[wpos] = sce[i - 1];
        fp ^= rabin_tables.U[om];
        x = fp >> 55;
        fp <<= 8;
        fp |= sce[i - 1];
        fp ^= rabin_tables.T[x];

        if (i >= min) {
            if (i < avg) {
                if ((fp & sml_mask) == BREAKMARK_VALUE)
                    break;
            } else if ((fp & lrg_mask) == BREAKMARK_VALUE)
                break;
        }
        ++i;
    }
    return i;
}