MACTABLE_BLOCKSIZE
if (mfp->mf_mac_used < 2*MACTABLE_BLOCKSIZE-1) /* minimum size */
n = 2*MACTABLE_BLOCKSIZE-1;
else if (mfp->mf_mac_used + 2*MACTABLE_BLOCKSIZE < mfp->mf_mac_allocated) /* reduce size */
n = mfp->mf_mac_allocated - MACTABLE_BLOCKSIZE;
n = mfp->mf_mac_allocated + MACTABLE_BLOCKSIZE;