in lz4.cpp [1852:1858]
static size_t read_long_length_no_check(const BYTE** pp)
{
size_t b, l = 0;
do { b = **pp; (*pp)++; l += b; } while (b==255);
DEBUGLOG(6, "read_long_length_no_check: +length=%zu using %zu input bytes", l, l/255 + 1)
return l;
}