svm_range_split
r = svm_range_split(prange, prange->start, new_last, &tail);
r = svm_range_split(prange, new_start, prange->last, &head);
svm_range_split(prange, prange->start, start - 1, &tail);
svm_range_split(tail, last + 1, tail->last, &head);