X-Git-Url: https://git.distorted.org.uk/~mdw/catacomb/blobdiff_plain/d3f33b9a37f45bc5809af314b1b436b712d59a80..48af823d9b5218ce32d7590b786d3b1cd089b68c:/symm/des-base.h

diff --git a/symm/des-base.h b/symm/des-base.h
index 7e55e044..325af534 100644
--- a/symm/des-base.h
+++ b/symm/des-base.h
@@ -122,27 +122,39 @@ extern const uint32 des_sp[8][64];
  *
  * We can implement this efficiently using our permutation machinery.
  * Writing ~k for index bit @k@ inverted, this permutation reflects the index
- * transformation given by ~0, 2, 1, ~5, ~4, ~3.  The following sequence of
- * operations is traditional.  Essentially this is an antitranspose -- a
- * reflection about the antidiagonal -- followed by a couple of fixup stages.
+ * transformation given by ~0, 2, 1, ~5, ~4, ~3.  There's a traditional
+ * swizzle sequence for this, which we used to use, namely:
+ *
+ *					//  5,  4,  3,  2,  1,  0
+ *	TWIZZLE_XCPL (x, y, 2);		// ~2,  4,  3, ~5,  1,  0
+ *	SWIZZLE_XCPL2(x, y, 1, 4);	// ~2, ~1,  3, ~5, ~4,  0
+ *	SWIZZLE_XCPL2(x, y, 0, 3);	// ~2, ~1, ~0, ~5, ~4, ~3
+ *	SWIZZLE_XCPL2(x, y, 3, 4);	// ~2,  0,  1, ~5, ~4, ~3
+ *	TWIZZLE_XCPL (x, y, 4);		// ~0,  2,  1, ~5, ~4, ~3
+ *
+ * Essentially this is an antitranspose -- a reflection about the
+ * antidiagonal -- followed by a couple of fixup stages.  But the non-twizzle
+ * steps require more operations, and it's easy to find a sequence which
+ * always acts on the (current) index bit 5, moving it to where it's wanted,
+ * and inverting it if necessary, so we only need twizzles.
  */
 
-#define DES_IP(x, y) do {		/*  5,  4,  3,  2,  1,  0 */	\
-  TWIZZLE_XCPL (x, y, 2);		/* ~2,  4,  3, ~5,  1,  0 */	\
-  SWIZZLE_XCPL2(x, y, 1, 4);		/* ~2, ~1,  3, ~5, ~4,  0 */	\
-  SWIZZLE_XCPL2(x, y, 0, 3);		/* ~2, ~1, ~0, ~5, ~4, ~3 */	\
-  SWIZZLE_XCPL2(x, y, 3, 4);		/* ~2,  0,  1, ~5, ~4, ~3 */	\
-  TWIZZLE_XCPL (x, y, 4);		/* ~0,  2,  1, ~5, ~4, ~3 */	\
+#define DES_IP(x, y) do {						\
+  TWIZZLE_XCPL(x, y, 2);		/* ~2,  4,  3, ~5,  1,  0 */	\
+  TWIZZLE_XCPL(x, y, 4);		/* ~4,  2,  3, ~5,  1,  0 */	\
+  TWIZZLE_EXCH(x, y, 1);		/*  1,  2,  3, ~5, ~4,  0 */	\
+  TWIZZLE_EXCH(x, y, 3);		/*  3,  2,  1, ~5, ~4,  0 */	\
+  TWIZZLE_XCPL(x, y, 0);		/* ~0,  2,  1, ~5, ~4, ~3 */	\
   x = ROL32(x, 1); y = ROL32(y, 1);					\
 } while (0)
 
 #define DES_IPINV(x, y) do {						\
   x = ROR32(x, 1); y = ROR32(y, 1);	/* ~0,  2,  1, ~5, ~4, ~3 */	\
-  TWIZZLE_XCPL (x, y, 4);		/* ~2,  0,  1, ~5, ~4, ~3 */	\
-  SWIZZLE_XCPL2(x, y, 3, 4);		/* ~2, ~1, ~0, ~5, ~4, ~3 */	\
-  SWIZZLE_XCPL2(x, y, 0, 3);		/* ~2, ~1,  3, ~5, ~4,  0 */	\
-  SWIZZLE_XCPL2(x, y, 1, 4);		/* ~2,  4,  3, ~5,  1,  0 */	\
-  TWIZZLE_XCPL (x, y, 2);		/*  5,  4,  3,  2,  1,  0 */	\
+  TWIZZLE_XCPL(x, y, 0);		/*  3,  2,  1, ~5, ~4,  0 */	\
+  TWIZZLE_EXCH(x, y, 3);		/*  1,  2,  3, ~5, ~4,  0 */	\
+  TWIZZLE_EXCH(x, y, 1);		/* ~4,  2,  3, ~5,  1,  0 */	\
+  TWIZZLE_XCPL(x, y, 4);		/*  3,  2,  1, ~5, ~4,  0 */	\
+  TWIZZLE_XCPL(x, y, 2);		/*  5,  4,  3,  2,  1,  0 */	\
 } while (0)
 
 /* --- @DES_EBLK@, @DES_DBLK@ --- *