AES-CFB[18] 2x optimization. Well, I bet nobody cares about AES-CFB1

/* This expects a single block of size nbits for both in and out. Note that

   it corrupts any extra bits in the last byte of out */

/* Untested, once it is working, it will be optimised */

void AES_cfbr_encrypt_block(const unsigned char *in,unsigned char *out,

			    const int nbits,const AES_KEY *key,

			    unsigned char *ivec,const int enc)

    {

    int n;

    int n,rem,num;

    unsigned char ovec[AES_BLOCK_SIZE*2];

    assert(in && out && key && ivec);

    if(enc)

	{

	/* construct the new IV */

	AES_encrypt(ivec,ovec,key);

	/* encrypt the input */

	for(n=0 ; n < (nbits+7)/8 ; ++n)

	    out[n]=in[n]^ovec[n];

    if (nbits<=0 || nbits>128) return;

	/* fill in the first half of the new IV with the current IV */

	memcpy(ovec,ivec,AES_BLOCK_SIZE);

	/* and put the ciphertext in the second half */

	memcpy(ovec+AES_BLOCK_SIZE,out,(nbits+7)/8);

	/* shift ovec left most of the bits... */

	memmove(ovec,ovec+nbits/8,AES_BLOCK_SIZE+(nbits%8 ? 1 : 0));

	/* now the remaining bits */

	if(nbits%8 != 0)

	    for(n=0 ; n < AES_BLOCK_SIZE ; ++n)

		{

		ovec[n]<<=nbits%8;

		ovec[n]|=ovec[n+1]>>(8-nbits%8);

		}

	/* finally, move it back into place */

	memcpy(ivec,ovec,AES_BLOCK_SIZE);

	}

	/* construct the new IV */

	AES_encrypt(ivec,ivec,key);

	num = (nbits+7)/8;

	if (enc)	/* encrypt the input */

	    for(n=0 ; n < num ; ++n)

		out[n] = (ovec[AES_BLOCK_SIZE+n] = in[n] ^ ivec[n]);

	else		/* decrypt the input */

	    for(n=0 ; n < num ; ++n)

		out[n] = (ovec[AES_BLOCK_SIZE+n] = in[n]) ^ ivec[n];

	/* shift ovec left... */

	rem = nbits%8;

	num = nbits/8;

	if(rem==0)

	    memcpy(ivec,ovec+num,AES_BLOCK_SIZE);

	else

	{

	/* construct the new IV in the first half of ovec */

	AES_encrypt(ivec,ovec,key);

	/* decrypt the input */

	for(n=0 ; n < (nbits+7)/8 ; ++n)

	    out[n]=in[n]^ovec[n];

	/* fill in the first half of the new IV with the current IV */

	memcpy(ovec,ivec,AES_BLOCK_SIZE);

	/* append the ciphertext */

	memcpy(ovec+AES_BLOCK_SIZE,in,(nbits+7)/8);

	/* shift ovec left most of the bits... */

	memmove(ovec,ovec+nbits/8,AES_BLOCK_SIZE+(nbits%8 ? 1 : 0));

	/* now the remaining bits */

	if(nbits%8 != 0)

	    for(n=0 ; n < AES_BLOCK_SIZE ; ++n)

		{

		ovec[n]<<=nbits%8;

		ovec[n]|=ovec[n+1]>>(8-nbits%8);

		}

	/* finally, move it back into place */

	memcpy(ivec,ovec,AES_BLOCK_SIZE);

	}

		ivec[n] = ovec[n+num]<<rem | ovec[n+num+1]>>(8-rem);

    /* it is not necessary to cleanse ovec, since the IV is not secret */

    }