/* SPDX-License-Identifier: GPL-2.0-or-later */

  /*
   * CTR: Counter mode
   *
   * Copyright (c) 2007 Herbert Xu <herbert@gondor.apana.org.au>

   */
  
  #ifndef _CRYPTO_CTR_H
  #define _CRYPTO_CTR_H

  #include <crypto/algapi.h>
  #include <crypto/internal/skcipher.h>
  #include <linux/string.h>
  #include <linux/types.h>

  #define CTR_RFC3686_NONCE_SIZE 4
  #define CTR_RFC3686_IV_SIZE 8
  #define CTR_RFC3686_BLOCK_SIZE 16

  static inline int crypto_ctr_encrypt_walk(struct skcipher_request *req,
  					  void (*fn)(struct crypto_skcipher *,
  						     const u8 *, u8 *))
  {
  	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
  	int blocksize = crypto_skcipher_chunksize(tfm);
  	u8 buf[MAX_CIPHER_BLOCKSIZE];
  	struct skcipher_walk walk;
  	int err;
  
  	/* avoid integer division due to variable blocksize parameter */
  	if (WARN_ON_ONCE(!is_power_of_2(blocksize)))
  		return -EINVAL;
  
  	err = skcipher_walk_virt(&walk, req, false);
  
  	while (walk.nbytes > 0) {
  		u8 *dst = walk.dst.virt.addr;
  		u8 *src = walk.src.virt.addr;
  		int nbytes = walk.nbytes;
  		int tail = 0;
  
  		if (nbytes < walk.total) {
  			tail = walk.nbytes & (blocksize - 1);
  			nbytes -= tail;
  		}
  
  		do {
  			int bsize = min(nbytes, blocksize);
  
  			fn(tfm, walk.iv, buf);
  
  			crypto_xor_cpy(dst, src, buf, bsize);
  			crypto_inc(walk.iv, blocksize);
  
  			dst += bsize;
  			src += bsize;
  			nbytes -= bsize;
  		} while (nbytes > 0);
  
  		err = skcipher_walk_done(&walk, tail);
  	}
  	return err;
  }

  #endif  /* _CRYPTO_CTR_H */