Split ecc_generic_redc into two functions ecc_pp1_redc and ecc_pm1_redc.

ChangeLog

 2014-08-28  Niels Möller  <nisse@lysator.liu.se>
 
+	* ecc-generic-redc.c (ecc_generic_redc): Deleted file and
+	function. Split into...
+	* ecc-pp1-redc.c (ecc_pp1_redc): New file and function.
+	* ecc-pm1-redc.c (ecc_pm1_redc): New file and function.
+	* ecc-internal.h: Updated declarations.
+	* Makefile.in (hogweed_SOURCES): Replace ecc-generic-redc.c by
+	ecc-pp1-redc.c and ecc-pm1-redc.c.
+	* ecc-192.c: Use ecc_pp1_redc (benchmarking only).
+	* ecc-224.c: Use ecc_pm1_redc when applicable.
+	* ecc-256.c: Use ecc_pp1_redc when applicable.
+	* ecc-384.c: Use ecc_pp1_redc (benchmarking only).
+	* ecc-521.c: Use ecc_pp1_redc (benchmarking only).
+	* testsuite/ecc-redc-test.c (test_main): Replace use of
+	ecc_generic_redc by ecc_pp1_redc and ecc_pm1_redc.
+
 	* eccdata.c (output_curve): Don't output ecc_redc_g.
 	* ecc-internal.h (struct ecc_curve): Deleted unused field redc_g.
 	Updated all instances.

Makefile.in

@@ -162,7 +162,7 @@ hogweed_SOURCES = sexp.c sexp-format.c \
 		  sec-add-1.c sec-sub-1.c sec-modinv.c sec-tabselect.c \
 		  gmp-glue.c cnd-copy.c \
 		  ecc-mod.c ecc-generic-modp.c ecc-generic-modq.c \
-		  ecc-modp.c ecc-modq.c ecc-generic-redc.c \
+		  ecc-modp.c ecc-modq.c ecc-pp1-redc.c ecc-pm1-redc.c \
 		  ecc-192.c ecc-224.c ecc-256.c ecc-384.c ecc-521.c \
 		  ecc-25519.c \
 		  ecc-size.c ecc-j-to-a.c ecc-a-to-j.c \

ecc-192.c

@@ -127,7 +127,7 @@ const struct ecc_curve nettle_secp_192r1 =
   ECC_J_TO_A_ITCH (ECC_LIMB_SIZE),
 
   ecc_192_modp,
-  ecc_generic_redc,
+  ECC_REDC_SIZE >= 1 ? ecc_pp1_redc : NULL,
   ecc_192_modp,
   ecc_generic_modq,
 

ecc-224.c

@@ -54,6 +54,14 @@ ecc_224_modp (const struct ecc_curve *ecc, mp_limb_t *rp);
 
 #include "ecc-224.h"
 
+#if ECC_REDC_SIZE < 0
+# define ecc_224_redc ecc_pm1_redc
+#elif ECC_REDC_SIZE == 0
+# define ecc_224_redc NULL
+#else
+# error Configuration error
+#endif
+
 const struct ecc_curve nettle_secp_224r1 =
 {
   224,
@@ -71,8 +79,8 @@ const struct ecc_curve nettle_secp_224r1 =
   ECC_J_TO_A_ITCH (ECC_LIMB_SIZE),
 
   ecc_224_modp,
-  ecc_generic_redc,
-  USE_REDC ? ecc_generic_redc : ecc_224_modp,
+  ecc_224_redc,
+  USE_REDC ? ecc_224_redc : ecc_224_modp,
   ecc_generic_modq,
 
   ecc_mul_a,

ecc-256.c

@@ -55,8 +55,14 @@
 void
 ecc_256_redc (const struct ecc_curve *ecc, mp_limb_t *rp);
 #else /* !HAVE_NATIVE_ecc_256_redc */
-# define ecc_256_redc ecc_generic_redc
-#endif
+# if ECC_REDC_SIZE > 0 
+#   define ecc_256_redc ecc_pp1_redc
+# elif ECC_REDC_SIZE == 0
+#   define ecc_256_redc NULL
+# else
+#  error Configuration error
+# endif
+#endif /* !HAVE_NATIVE_ecc_256_redc */
 
 #if ECC_BMODP_SIZE < ECC_LIMB_SIZE
 #define ecc_256_modp ecc_generic_modp

ecc-384.c

@@ -164,7 +164,7 @@ const struct ecc_curve nettle_secp_384r1 =
   ECC_J_TO_A_ITCH (ECC_LIMB_SIZE),
 
   ecc_384_modp,
-  ECC_REDC_SIZE != 0 ? ecc_generic_redc : NULL,
+  ECC_REDC_SIZE > 0 ? ecc_pp1_redc : NULL,
   ecc_384_modp,
   ecc_generic_modq,
 

ecc-521.c

@@ -92,7 +92,7 @@ const struct ecc_curve nettle_secp_521r1 =
   ECC_J_TO_A_ITCH (ECC_LIMB_SIZE),
 
   ecc_521_modp,
-  ecc_generic_redc,
+  ECC_REDC_SIZE > 0 ? ecc_pp1_redc : NULL,
   ecc_521_modp,
   ecc_generic_modq,
 

ecc-internal.h

@@ -41,7 +41,8 @@
 
 /* Name mangling */
 #define ecc_generic_modp _nettle_ecc_generic_modp
-#define ecc_generic_redc _nettle_ecc_generic_redc
+#define ecc_pp1_redc _nettle_ecc_pp1_redc
+#define ecc_pm1_redc _nettle_ecc_pm1_redc
 #define ecc_generic_modq _nettle_ecc_generic_modq
 #define ecc_modp_add _nettle_ecc_modp_add
 #define ecc_modp_sub _nettle_ecc_modp_sub
@@ -174,7 +175,8 @@ struct ecc_curve
 
 /* In-place reduction. */
 ecc_mod_func ecc_generic_modp;
-ecc_mod_func ecc_generic_redc;
+ecc_mod_func ecc_pp1_redc;
+ecc_mod_func ecc_pm1_redc;
 ecc_mod_func ecc_generic_modq;
 
 

ecc-pm1-redc.c

+/* ecc-pm1-redc.c
+
+   Copyright (C) 2013, 2014 Niels Möller
+
+   This file is part of GNU Nettle.
+
+   GNU Nettle is free software: you can redistribute it and/or
+   modify it under the terms of either:
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at your
+       option) any later version.
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at your
+       option) any later version.
+
+   or both in parallel, as here.
+
+   GNU Nettle is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see http://www.gnu.org/licenses/.
+*/
+
+/* Development of Nettle's ECC support was funded by the .SE Internet Fund. */
+
+#if HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <assert.h>
+
+#include "ecc-internal.h"
+
+/* Use that 1 = - (p - 1) (mod p), and that at least one low limb of p
+   - 1 is zero. */
+void
+ecc_pm1_redc (const struct ecc_curve *ecc, mp_limb_t *rp)
+{
+  unsigned i;
+  mp_limb_t hi, cy;
+  unsigned shift = ecc->size * GMP_NUMB_BITS - ecc->bit_size;
+  mp_size_t k = -ecc->redc_size;
+  
+  assert (k > 0);
+
+  for (i = 0; i < ecc->size; i++)
+    rp[i] = mpn_submul_1 (rp + i + k,
+			  ecc->redc_ppm1, ecc->size - k, rp[i]);
+  hi = mpn_sub_n (rp, rp + ecc->size, rp, ecc->size);
+  cy = cnd_add_n (hi, rp, ecc->p, ecc->size);
+  assert (cy == hi);
+
+  if (shift > 0)
+    {
+      /* Result is always < 2p, provided that
+	 2^shift * Bmodp_shifted <= p */
+      hi = (rp[ecc->size - 1] >> (GMP_NUMB_BITS - shift));
+      rp[ecc->size - 1] = (rp[ecc->size - 1]
+			   & (((mp_limb_t) 1 << (GMP_NUMB_BITS - shift)) - 1))
+	+ mpn_addmul_1 (rp, ecc->Bmodp_shifted, ecc->size-1, hi);
+    }
+}

ecc-generic-redc.c → ecc-pp1-redc.c

-/* ecc-generic-redc.c
+/* ecc-pp1-redc.c
 
-   Copyright (C) 2013 Niels Möller
+   Copyright (C) 2013, 2014 Niels Möller
 
    This file is part of GNU Nettle.
 
@@ -39,56 +39,33 @@
 
 #include "ecc-internal.h"
 
+/* Use that 1 = p + 1 (mod p), and that at least one low limb of p + 1
+   is zero. */
 void
-ecc_generic_redc (const struct ecc_curve *ecc, mp_limb_t *rp)
+ecc_pp1_redc (const struct ecc_curve *ecc, mp_limb_t *rp)
 {
   unsigned i;
   mp_limb_t hi, cy;
   unsigned shift = ecc->size * GMP_NUMB_BITS - ecc->bit_size;
   mp_size_t k = ecc->redc_size;
   
-  assert (k != 0);
-  if (k > 0)    
+  assert (k > 0);
+
+  for (i = 0; i < ecc->size; i++)
+    rp[i] = mpn_addmul_1 (rp + i + k,
+			  ecc->redc_ppm1, ecc->size - k, rp[i]);
+  hi = mpn_add_n (rp, rp, rp + ecc->size, ecc->size);
+  if (shift > 0)
     {
-      /* Use that 1 = p + 1, and that at least one low limb of p + 1 is zero. */
-      for (i = 0; i < ecc->size; i++)
-	rp[i] = mpn_addmul_1 (rp + i + k,
-			      ecc->redc_ppm1, ecc->size - k, rp[i]);
-      hi = mpn_add_n (rp, rp, rp + ecc->size, ecc->size);
-      if (shift > 0)
-	{
-	  hi = (hi << shift) | (rp[ecc->size - 1] >> (GMP_NUMB_BITS - shift));
-	  rp[ecc->size - 1] = (rp[ecc->size - 1]
-			       & (((mp_limb_t) 1 << (GMP_NUMB_BITS - shift)) - 1))
-	    + mpn_addmul_1 (rp, ecc->Bmodp_shifted, ecc->size-1, hi);
+      hi = (hi << shift) | (rp[ecc->size - 1] >> (GMP_NUMB_BITS - shift));
+      rp[ecc->size - 1] = (rp[ecc->size - 1]
+			   & (((mp_limb_t) 1 << (GMP_NUMB_BITS - shift)) - 1))
+	+ mpn_addmul_1 (rp, ecc->Bmodp_shifted, ecc->size-1, hi);
 	  
-	}
-      else
-	{
-	  cy = cnd_sub_n (hi, rp, ecc->p, ecc->size);
-	  assert (cy == hi);      
-	}
     }
   else
     {
-      /* Use that 1 = - (p - 1), and that at least one low limb of p -
-	 1 is zero. */
-      k = -k;
-      for (i = 0; i < ecc->size; i++)
-	rp[i] = mpn_submul_1 (rp + i + k,
-			      ecc->redc_ppm1, ecc->size - k, rp[i]);
-      hi = mpn_sub_n (rp, rp + ecc->size, rp, ecc->size);
-      cy = cnd_add_n (hi, rp, ecc->p, ecc->size);
-      assert (cy == hi);
-
-      if (shift > 0)
-	{
-	  /* Result is always < 2p, provided that
-	     2^shift * Bmodp_shifted <= p */
-	  hi = (rp[ecc->size - 1] >> (GMP_NUMB_BITS - shift));
-	  rp[ecc->size - 1] = (rp[ecc->size - 1]
-			       & (((mp_limb_t) 1 << (GMP_NUMB_BITS - shift)) - 1))
-	    + mpn_addmul_1 (rp, ecc->Bmodp_shifted, ecc->size-1, hi);
-	}
+      cy = cnd_sub_n (hi, rp, ecc->p, ecc->size);
+      assert (cy == hi);      
     }
 }

testsuite/ecc-redc-test.c

@@ -87,14 +87,18 @@ test_main (void)
 	    }
 
 	  mpn_copyi (m, a, 2*ecc->size);
-	  ecc_generic_redc (ecc, m);
+	  if (ecc->redc_size > 0)
+	    ecc_pp1_redc (ecc, m);
+	  else
+	    ecc_pm1_redc (ecc, m);
+
 	  if (mpn_cmp (m, ecc->p, ecc->size) >= 0)
 	    mpn_sub_n (m, m, ecc->p, ecc->size);
 
 	  if (mpn_cmp (m, ref, ecc->size))
 	    {
-	      fprintf (stderr, "ecc_generic_redc failed: bit_size = %u\n",
-		       ecc->bit_size);
+	      fprintf (stderr, "ecc_p%c1_redc failed: bit_size = %u\n",
+		       ecc->redc_size > 0 ? 'p' : 'm', ecc->bit_size);
 	      gmp_fprintf (stderr, "a   = %Nx\n", a, 2*ecc->size);
 	      gmp_fprintf (stderr, "m   = %Nx (bad)\n", m, ecc->size);
 	      gmp_fprintf (stderr, "ref = %Nx\n", ref, ecc->size);