Reduce code size for Twofish key-setup and remove key dependend branch

* cipher/twofish.c (poly_to_exp): Increase size by one, change type
from byte to u16 and insert '492' to index 0.
(exp_to_poly): Increase size by 256, let new cells have zero value.
(CALC_S): Execute unconditionally with help of modified tables.
(do_twofish_setkey): Change type for 'tmp' to 'unsigned int'; Un-unroll
CALC_K256 and CALC_K phases to reduce generated object size.
--

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

1 files changed, 26 insertions, 50 deletions

diff --git a/cipher/twofish.c b/cipher/twofish.c
index 3ee2be51..11e60a74 100644
--- a/cipher/twofish.c
+++ b/cipher/twofish.c
@@ -356,7 +356,8 @@ static const u32 mds[4][256] = {
  * see a non-horrible way of avoiding them, and I did manage to group the
  * statements so that each if covers four group multiplications. */
 
-static const byte poly_to_exp[255] = {
+static const u16 poly_to_exp[256] = {
+   492,
    0x00, 0x01, 0x17, 0x02, 0x2E, 0x18, 0x53, 0x03, 0x6A, 0x2F, 0x93, 0x19,
    0x34, 0x54, 0x45, 0x04, 0x5C, 0x6B, 0xB6, 0x30, 0xA6, 0x94, 0x4B, 0x1A,
    0x8C, 0x35, 0x81, 0x55, 0xAA, 0x46, 0x0D, 0x05, 0x24, 0x5D, 0x87, 0x6C,
@@ -381,7 +382,7 @@ static const byte poly_to_exp[255] = {
    0x85, 0xC8, 0xA1
 };
 
-static const byte exp_to_poly[492] = {
+static const byte exp_to_poly[492 + 256] = {
    0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x4D, 0x9A, 0x79, 0xF2,
    0xA9, 0x1F, 0x3E, 0x7C, 0xF8, 0xBD, 0x37, 0x6E, 0xDC, 0xF5, 0xA7, 0x03,
    0x06, 0x0C, 0x18, 0x30, 0x60, 0xC0, 0xCD, 0xD7, 0xE3, 0x8B, 0x5B, 0xB6,
@@ -422,7 +423,7 @@ static const byte exp_to_poly[492] = {
    0x3F, 0x7E, 0xFC, 0xB5, 0x27, 0x4E, 0x9C, 0x75, 0xEA, 0x99, 0x7F, 0xFE,
    0xB1, 0x2F, 0x5E, 0xBC, 0x35, 0x6A, 0xD4, 0xE5, 0x87, 0x43, 0x86, 0x41,
    0x82, 0x49, 0x92, 0x69, 0xD2, 0xE9, 0x9F, 0x73, 0xE6, 0x81, 0x4F, 0x9E,
-   0x71, 0xE2, 0x89, 0x5F, 0xBE, 0x31, 0x62, 0xC4, 0xC5, 0xC7, 0xC3, 0xCB
+   0x71, 0xE2, 0x89, 0x5F, 0xBE, 0x31, 0x62, 0xC4, 0xC5, 0xC7, 0xC3, 0xCB,
 };
 
 
@@ -494,14 +495,15 @@ static byte calc_sb_tbl[512] = {
     0x6F, 0x16, 0x9D, 0x25, 0x36, 0x86, 0x42, 0x56,
     0x4A, 0x55, 0x5E, 0x09, 0xC1, 0xBE, 0xE0, 0x91
 };
+
 /* Macro to perform one column of the RS matrix multiplication.  The
  * parameters a, b, c, and d are the four bytes of output; i is the index
  * of the key bytes, and w, x, y, and z, are the column of constants from
  * the RS matrix, preprocessed through the poly_to_exp table. */
 
 #define CALC_S(a, b, c, d, i, w, x, y, z) \
-   if (key[i]) { \
-      tmp = poly_to_exp[key[i] - 1]; \
+   { \
+      tmp = poly_to_exp[key[i]]; \
       (a) ^= exp_to_poly[tmp + (w)]; \
       (b) ^= exp_to_poly[tmp + (x)]; \
       (c) ^= exp_to_poly[tmp + (y)]; \
@@ -600,7 +602,7 @@ do_twofish_setkey (TWOFISH_context *ctx, const byte *key, const unsigned keylen)
   byte si = 0, sj = 0, sk = 0, sl = 0, sm = 0, sn = 0, so = 0, sp = 0;
 
   /* Temporary for CALC_S. */
-  byte tmp;
+  unsigned int tmp;
 
   /* Flags for self-test. */
   static int initialized = 0;
@@ -668,28 +670,15 @@ do_twofish_setkey (TWOFISH_context *ctx, const byte *key, const unsigned keylen)
           CALC_SB256_2( i, calc_sb_tbl[j], calc_sb_tbl[k] );
 	}
 
-      /* Calculate whitening and round subkeys.  The constants are
-       * indices of subkeys, preprocessed through q0 and q1. */
-      CALC_K256 (w, 0, 0xA9, 0x75, 0x67, 0xF3);
-      CALC_K256 (w, 2, 0xB3, 0xC6, 0xE8, 0xF4);
-      CALC_K256 (w, 4, 0x04, 0xDB, 0xFD, 0x7B);
-      CALC_K256 (w, 6, 0xA3, 0xFB, 0x76, 0xC8);
-      CALC_K256 (k, 0, 0x9A, 0x4A, 0x92, 0xD3);
-      CALC_K256 (k, 2, 0x80, 0xE6, 0x78, 0x6B);
-      CALC_K256 (k, 4, 0xE4, 0x45, 0xDD, 0x7D);
-      CALC_K256 (k, 6, 0xD1, 0xE8, 0x38, 0x4B);
-      CALC_K256 (k, 8, 0x0D, 0xD6, 0xC6, 0x32);
-      CALC_K256 (k, 10, 0x35, 0xD8, 0x98, 0xFD);
-      CALC_K256 (k, 12, 0x18, 0x37, 0xF7, 0x71);
-      CALC_K256 (k, 14, 0xEC, 0xF1, 0x6C, 0xE1);
-      CALC_K256 (k, 16, 0x43, 0x30, 0x75, 0x0F);
-      CALC_K256 (k, 18, 0x37, 0xF8, 0x26, 0x1B);
-      CALC_K256 (k, 20, 0xFA, 0x87, 0x13, 0xFA);
-      CALC_K256 (k, 22, 0x94, 0x06, 0x48, 0x3F);
-      CALC_K256 (k, 24, 0xF2, 0x5E, 0xD0, 0xBA);
-      CALC_K256 (k, 26, 0x8B, 0xAE, 0x30, 0x5B);
-      CALC_K256 (k, 28, 0x84, 0x8A, 0x54, 0x00);
-      CALC_K256 (k, 30, 0xDF, 0xBC, 0x23, 0x9D);
+      /* Calculate whitening and round subkeys. */
+      for (i = 0; i < 8; i += 2)
+	{
+	  CALC_K256 ( w, i, q0[i], q1[i], q0[i + 1], q1[i + 1] );
+	}
+      for (j = 0; j < 32; j += 2, i += 2)
+	{
+	  CALC_K256 ( k, j, q0[i], q1[i], q0[i + 1], q1[i + 1] );
+	}
     }
   else
     {
@@ -699,28 +688,15 @@ do_twofish_setkey (TWOFISH_context *ctx, const byte *key, const unsigned keylen)
           CALC_SB_2( i, calc_sb_tbl[j], calc_sb_tbl[k] );
         }
 
-      /* Calculate whitening and round subkeys.  The constants are
-       * indices of subkeys, preprocessed through q0 and q1. */
-      CALC_K (w, 0, 0xA9, 0x75, 0x67, 0xF3);
-      CALC_K (w, 2, 0xB3, 0xC6, 0xE8, 0xF4);
-      CALC_K (w, 4, 0x04, 0xDB, 0xFD, 0x7B);
-      CALC_K (w, 6, 0xA3, 0xFB, 0x76, 0xC8);
-      CALC_K (k, 0, 0x9A, 0x4A, 0x92, 0xD3);
-      CALC_K (k, 2, 0x80, 0xE6, 0x78, 0x6B);
-      CALC_K (k, 4, 0xE4, 0x45, 0xDD, 0x7D);
-      CALC_K (k, 6, 0xD1, 0xE8, 0x38, 0x4B);
-      CALC_K (k, 8, 0x0D, 0xD6, 0xC6, 0x32);
-      CALC_K (k, 10, 0x35, 0xD8, 0x98, 0xFD);
-      CALC_K (k, 12, 0x18, 0x37, 0xF7, 0x71);
-      CALC_K (k, 14, 0xEC, 0xF1, 0x6C, 0xE1);
-      CALC_K (k, 16, 0x43, 0x30, 0x75, 0x0F);
-      CALC_K (k, 18, 0x37, 0xF8, 0x26, 0x1B);
-      CALC_K (k, 20, 0xFA, 0x87, 0x13, 0xFA);
-      CALC_K (k, 22, 0x94, 0x06, 0x48, 0x3F);
-      CALC_K (k, 24, 0xF2, 0x5E, 0xD0, 0xBA);
-      CALC_K (k, 26, 0x8B, 0xAE, 0x30, 0x5B);
-      CALC_K (k, 28, 0x84, 0x8A, 0x54, 0x00);
-      CALC_K (k, 30, 0xDF, 0xBC, 0x23, 0x9D);
+      /* Calculate whitening and round subkeys. */
+      for (i = 0; i < 8; i += 2)
+	{
+	  CALC_K ( w, i, q0[i], q1[i], q0[i + 1], q1[i + 1] );
+	}
+      for (j = 0; j < 32; j += 2, i += 2)
+	{
+	  CALC_K ( k, j, q0[i], q1[i], q0[i + 1], q1[i + 1] );
+	}
     }
 
   return 0;