Avoid division by spec->blocksize in cipher mode handlers

* cipher/cipher-internal.h (_gcry_blocksize_shift): New.
* cipher/cipher-cbc.c (_gcry_cipher_cbc_encrypt)
(_gcry_cipherp_cbc_decrypt): Use bit-level operations instead of
division to get number of blocks and check input length against
blocksize.
* cipher/cipher-cfb.c (_gcry_cipher_cfb_encrypt)
(_gcry_cipher_cfb_decrypt): Ditto.
* cipher/cipher-cmac.c (_gcry_cmac_write): Ditto.
* cipher/cipher-ctr.c (_gcry_cipher_ctr_crypt): Ditto.
* cipher/cipher-ofb.c (_gcry_cipher_ofb_encrypt)
(_gcry_cipher_ofb_decrypt): Ditto.
--

Integer division was causing 10 to 20 cycles per call overhead
for cipher modes on x86-64.

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>

1 files changed, 6 insertions, 10 deletions

diff --git a/cipher/cipher-cmac.c b/cipher/cipher-cmac.c
index 30567b7f..321ab9ea 100644
--- a/cipher/cipher-cmac.c
+++ b/cipher/cipher-cmac.c
@@ -38,7 +38,8 @@ _gcry_cmac_write (gcry_cipher_hd_t c, gcry_cmac_context_t *ctx,
 		  const byte * inbuf, size_t inlen)
 {
   gcry_cipher_encrypt_t enc_fn = c->spec->encrypt;
-  const unsigned int blocksize = c->spec->blocksize;
+  size_t blocksize_shift = _gcry_blocksize_shift(c);
+  size_t blocksize = 1 << blocksize_shift;
   byte outbuf[MAX_BLOCKSIZE];
   unsigned int burn = 0;
   unsigned int nblocks;
@@ -46,11 +47,6 @@ _gcry_cmac_write (gcry_cipher_hd_t c, gcry_cmac_context_t *ctx,
   if (ctx->tag)
     return GPG_ERR_INV_STATE;
 
-  /* Tell compiler that we require a cipher with a 64bit or 128 bit block
-   * length, to allow better optimization of this function.  */
-  if (blocksize > 16 || blocksize < 8 || blocksize & (8 - 1))
-    return GPG_ERR_INV_CIPHER_MODE;
-
   if (!inbuf)
     return GPG_ERR_INV_ARG;
 
@@ -78,12 +74,12 @@ _gcry_cmac_write (gcry_cipher_hd_t c, gcry_cmac_context_t *ctx,
 
   if (c->bulk.cbc_enc && inlen > blocksize)
     {
-      nblocks = inlen / blocksize;
-      nblocks -= (nblocks * blocksize == inlen);
+      nblocks = inlen >> blocksize_shift;
+      nblocks -= ((nblocks << blocksize_shift) == inlen);
 
       c->bulk.cbc_enc (&c->context.c, ctx->u_iv.iv, outbuf, inbuf, nblocks, 1);
-      inbuf += nblocks * blocksize;
-      inlen -= nblocks * blocksize;
+      inbuf += nblocks << blocksize_shift;
+      inlen -= nblocks << blocksize_shift;
 
       wipememory (outbuf, sizeof (outbuf));
     }