Functions for mpn <-> mpz conversions.

1 files changed, 146 insertions, 0 deletions

diff --git a/gmp-glue.c b/gmp-glue.c
new file mode 100644
index 00000000..5e3a9c2a
--- /dev/null
+++ b/gmp-glue.c
@@ -0,0 +1,146 @@
+/* gmp-glue.c */
+
+/* nettle, low-level cryptographics library
+ *
+ * Copyright (C) 2013 Niels Möller
+ *  
+ * The nettle library is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 of the License, or (at your
+ * option) any later version.
+ * 
+ * The nettle library 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 Lesser General Public
+ * License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with the nettle library; see the file COPYING.LIB.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+ * MA 02111-1301, USA.
+ */
+
+#include <assert.h>
+
+#include "gmp-glue.h"
+
+/* This implementation tries to make a minimal use of GMP internals.
+   We access and _mp_size and _mp_d, but not _mp_alloc. */
+
+/* Use macros compatible with gmp-impl.h. */
+#define ABS(x) ((x) >= 0 ? (x) : -(x))
+#define PTR(x) ((x)->_mp_d)
+#define SIZ(x) ((x)->_mp_size)
+#define ABSIZ(x) ABS (SIZ (x))
+
+#define MPN_NORMALIZE(xp, xn) do {		\
+    while ( (xn) > 0 && (xp)[xn-1] == 0)	\
+      (xn)--;					\
+  }  while (0)
+
+/* NOTE: Makes an unnecessary realloc if allocation is already large
+   enough, but looking at _mp_alloc may break in future GMP
+   versions. */
+#define MPZ_REALLOC(x, n) \
+  (ABSIZ(x) >= (n) ? PTR(x) : (_mpz_realloc ((x),(n)), PTR (x)))
+
+#define MPZ_NEWALLOC MPZ_REALLOC
+
+int
+_mpz_cmp_limbs (mpz_srcptr a, const mp_limb_t *bp, mp_size_t bn)
+{
+  mp_size_t an = SIZ (a);
+  if (an < bn)
+    return -1;
+  if (an > bn)
+    return 1;
+  if (an == 0)
+    return 0;
+
+  return mpn_cmp (PTR(a), bp, an);
+}
+
+
+/* Read access to mpz numbers. */
+
+/* Return limb pointer, for read-only operations. Use mpz_size to get
+   the number of limbs. */
+const mp_limb_t *
+_mpz_read_limbs (mpz_srcptr x)
+{
+  return PTR (x);
+}
+
+/* Get a pointer to an n limb area, for read-only operation. n must be
+   greater or equal to the current size, and the mpz is zero-padded if
+   needed. */
+const mp_limb_t *
+_mpz_read_limbs_n (mpz_ptr x, mp_size_t n)
+{
+  mp_size_t xn = ABSIZ (x);
+
+  assert (xn <= n);
+
+  if (xn < n)
+    {
+      /* Makes an unnecessary realloc if allocation is already large
+	 enough. */
+      mpz_realloc (x, n);
+      mpn_zero (PTR(x) + xn, n - xn);
+    }
+
+  return PTR(x);
+}
+
+void
+_mpz_copy_limbs (mp_limb_t *xp, mpz_srcptr x, mp_size_t n)
+{
+  mp_size_t xn = ABSIZ (x);
+
+  assert (xn <= n);
+  mpn_copyi (xp, PTR(x), xn);
+  if (xn < n)
+    mpn_zero (xp + xn, n - xn);
+}
+
+/* Write access to mpz numbers. */
+
+/* Get a limb pointer for writing, previous contents may be
+   destroyed. */
+mp_limb_t *
+_mpz_write_limbs (mpz_ptr x, mp_size_t n)
+{
+  assert (n > 0);
+  return MPZ_NEWALLOC (x, n);
+}
+
+/* Get a limb pointer for writing, previous contents is intact. */
+mp_limb_t *
+_mpz_modify_limbs (mpz_ptr x, mp_size_t n)
+{
+  assert (n > 0);
+  return MPZ_REALLOC (x, n);
+}
+
+void
+_mpz_done_limbs (mpz_ptr x, mp_size_t n)
+{
+  assert (n >= 0);
+  MPN_NORMALIZE (PTR(x), n);
+
+  SIZ (x) = n;
+}
+
+/* Needs some ugly casts. */
+mpz_srcptr
+_mpz_init_mpn (mpz_ptr x, const mp_limb_t *xp, mp_size_t xs)
+{
+  mp_size_t xn = ABS (xs);
+  
+  MPN_NORMALIZE (xp, xn);
+
+  x->_mp_size = xs < 0 ? -xn : xn;
+  x->_mp_alloc = 0;
+  x->_mp_d = (mp_limb_t *) xp;
+  return x;
+}