Add support for left-to-right bitscanning, for use in modular

exponentiation.

diff --git a/mp-misc.c b/mp-misc.c
index 840f947..15c582d 100644 (file)
--- a/mp-misc.c
+++ b/mp-misc.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: mp-misc.c,v 1.2 2000/06/17 11:45:09 mdw Exp $
+ * $Id: mp-misc.c,v 1.3 2000/07/29 17:03:31 mdw Exp $
  *
  * Miscellaneous multiprecision support functions
  *
@@ -30,6 +30,10 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: mp-misc.c,v $
+ * Revision 1.3  2000/07/29 17:03:31  mdw
+ * Add support for left-to-right bitscanning, for use in modular
+ * exponentiation.
+ *
  * Revision 1.2  2000/06/17 11:45:09  mdw
  * Major memory management overhaul.  Added arena support.  Use the secure
  * arena for secret integers.  Replace and improve the MP management macros
@@ -93,4 +97,17 @@ void mp_minimize(mp *m)
 
 void mp_scan(mpscan *sc, const mp *m) { MP_SCAN(sc, m); }
 
+/* --- @mp_scan@ --- *
+ *
+ * Arguments:  @mpscan *sc@ = pointer to bitscanner block
+ *             @const mp *m@ = pointer to a multiprecision integer
+ *
+ * Returns:    ---
+ *
+ * Use:                Initializes a reverse bitscanner on a multiprecision
+ *             integer.
+ */
+
+void mp_rscan(mpscan *sc, const mp *m) { MP_RSCAN(sc, m); }
+
 /*----- That's all, folks -------------------------------------------------*/

diff --git a/mp.h b/mp.h
index 12003d0..5bc465d 100644 (file)
--- a/mp.h
+++ b/mp.h
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: mp.h,v 1.8 2000/06/22 19:02:01 mdw Exp $
+ * $Id: mp.h,v 1.9 2000/07/29 17:03:31 mdw Exp $
  *
  * Simple multiprecision arithmetic
  *
@@ -30,6 +30,10 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: mp.h,v $
+ * Revision 1.9  2000/07/29 17:03:31  mdw
+ * Add support for left-to-right bitscanning, for use in modular
+ * exponentiation.
+ *
  * Revision 1.8  2000/06/22 19:02:01  mdw
  * Add new functions.
  *
@@ -420,13 +424,36 @@ extern void mp_scan(mpscan */*sc*/, const mp */*m*/);
   MPSCAN_INITX(_sc, _mm->v, _mm->vl);                                  \
 } while (0)
 
+/* --- @mp_rscan@ --- *
+ *
+ * Arguments:  @mpscan *sc@ = pointer to bitscanner block
+ *             @const mp *m@ = pointer to a multiprecision integer
+ *
+ * Returns:    ---
+ *
+ * Use:                Initializes a reverse bitscanner on a multiprecision
+ *             integer.
+ */
+
+extern void mp_rscan(mpscan */*sc*/, const mp */*m*/);
+
+#define MP_RSCAN(sc, m) do {                                           \
+  const mp *_mm = (m);                                                 \
+  mpscan *_sc = (sc);                                                  \
+  MPSCAN_RINITX(_sc, _mm->v, _mm->vl);                                 \
+} while (0)
+
 /* --- Other bitscanning aliases --- */
 
 #define mp_step mpscan_step
 #define mp_bit mpscan_bit
+#define mp_rstep mpscan_rstep
+#define mp_rbit mpscan_rbit
 
 #define MP_STEP MPSCAN_STEP
 #define MP_BIT MPSCAN_BIT
+#define MP_RSTEP MPSCAN_RSTEP
+#define MP_RBIT MPSCAN_RBIT
 
 /*----- Loading and storing -----------------------------------------------*/
 

diff --git a/mpscan.c b/mpscan.c
index cbfd138..0a5b4f0 100644 (file)
--- a/mpscan.c
+++ b/mpscan.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: mpscan.c,v 1.2 1999/11/13 01:55:10 mdw Exp $
+ * $Id: mpscan.c,v 1.3 2000/07/29 17:03:31 mdw Exp $
  *
  * Sequential bit scan of multiprecision integers
  *
@@ -30,6 +30,10 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: mpscan.c,v $
+ * Revision 1.3  2000/07/29 17:03:31  mdw
+ * Add support for left-to-right bitscanning, for use in modular
+ * exponentiation.
+ *
  * Revision 1.2  1999/11/13 01:55:10  mdw
  * Fixed so that they compile.  Minor interface changes.
  *
@@ -42,7 +46,7 @@
 
 #include "mpscan.h"
 
-/*----- Main code ---------------------------------------------------------*/
+/*----- Right-to-left scanning --------------------------------------------*/
 
 /* --- @mpscan_initx@ --- *
  *
@@ -86,4 +90,48 @@ int mpscan_step(mpscan *m) { return (MPSCAN_STEP(m)); }
 
 int mpscan_bit(const mpscan *m) { return (MPSCAN_BIT(m)); }
 
+/*----- Left-to right-scanning --------------------------------------------*/
+
+/* --- @mpscan_rinitx@ --- *
+ *
+ * Arguments:  @mpscan *m@ = pointer to bitscanner structure
+ *             @const mpw *v, *vl@ = vector of words to scan
+ *
+ * Returns:    ---
+ *
+ * Use:                Initializes a reverse bitscanner from a low-level
+ *             vector-and-length representation of an integer.  Initially no
+ *             bit is ready; you must call @mpscan_rstep@ before anything
+ *             useful will come out.
+ */
+
+void mpscan_rinitx(mpscan *m, const mpw *v, const mpw *vl)
+{
+  MPSCAN_RINITX(m, v, vl);
+}
+
+/* --- @mpscan_rstep@ --- *
+ *
+ * Arguments:  @mpscan *m@ = pointer to bitscanner
+ *
+ * Returns:    Nonzero if there is another bit to read.
+ *
+ * Use:                Steps on to the next bit in the integer.  The macro version
+ *             evaluates its argument multiple times.
+ */
+
+int mpscan_rstep(mpscan *m) { return (MPSCAN_RSTEP(m)); }
+
+/* --- @mpscan_rbit@ --- *
+ *
+ * Arguments:  @const mpscan *m@ = pointer to bitscanner
+ *
+ * Returns:    The value of the current bit.
+ *
+ * Use:                Reads the value of the current bit looked at by a
+ *             reverse bitscanner.
+ */
+
+int mpscan_rbit(const mpscan *m) { return (MPSCAN_RBIT(m)); }
+
 /*----- That's all, folks -------------------------------------------------*/

diff --git a/mpscan.h b/mpscan.h
index 98f2a3d..619681d 100644 (file)
--- a/mpscan.h
+++ b/mpscan.h
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: mpscan.h,v 1.3 1999/12/10 23:29:48 mdw Exp $
+ * $Id: mpscan.h,v 1.4 2000/07/29 17:03:31 mdw Exp $
  *
  * Sequential bit scan of multiprecision integers
  *
@@ -30,6 +30,10 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: mpscan.h,v $
+ * Revision 1.4  2000/07/29 17:03:31  mdw
+ * Add support for left-to-right bitscanning, for use in modular
+ * exponentiation.
+ *
  * Revision 1.3  1999/12/10 23:29:48  mdw
  * Change header file guard names.
  *
@@ -62,7 +66,7 @@ typedef struct mpscan {
   int bits;                            /* Number of bits left in @w@ */
 } mpscan;
 
-/*----- Functions provided ------------------------------------------------*/
+/*----- Right-to-left scanning --------------------------------------------*/
 
 /* --- @mpscan_initx@ --- *
  *
@@ -97,8 +101,7 @@ extern void mpscan_initx(mpscan */*m*/, const mpw */*v*/, const mpw */*vl*/);
  */
 
 #define MPSCAN_STEP(m)                                                 \
-  ((m)->bits ? ((m)->w >>= 1,                                          \
-               (m)->bits--, 1) :                                       \
+  ((m)->bits ? ((m)->w >>= 1, (m)->bits--, 1) :                                \
    (m)->v < (m)->vl ? ((m)->w = *(m)->v++,                             \
                       (m)->bits = MPW_BITS - 1, 1) :                   \
    0)
@@ -119,6 +122,65 @@ extern int mpscan_step(mpscan */*m*/);
 
 extern int mpscan_bit(const mpscan */*m*/);
 
+/*----- Left-to right-scanning --------------------------------------------*/
+
+/* --- @mpscan_rinitx@ --- *
+ *
+ * Arguments:  @mpscan *m@ = pointer to bitscanner structure
+ *             @const mpw *v, *vl@ = vector of words to scan
+ *
+ * Returns:    ---
+ *
+ * Use:                Initializes a reverse bitscanner from a low-level
+ *             vector-and-length representation of an integer.  Initially no
+ *             bit is ready; you must call @mpscan_rstep@ before anything
+ *             useful will come out.
+ */
+
+#define MPSCAN_RINITX(m_, v_, vl_) do {                                        \
+  mpscan *_m = (m_);                                                   \
+  _m->v = (v_);                                                                \
+  _m->vl = (vl_);                                                      \
+  while (_m->vl > _m->v && !_m->vl[-1])                                        \
+    _m->vl--;                                                          \
+  _m->bits = 0;                                                                \
+} while (0)
+
+extern void mpscan_rinitx(mpscan */*m*/,
+                         const mpw */*v*/, const mpw */*vl*/);
+
+/* --- @mpscan_rstep@ --- *
+ *
+ * Arguments:  @mpscan *m@ = pointer to bitscanner
+ *
+ * Returns:    Nonzero if there is another bit to read.
+ *
+ * Use:                Steps on to the next bit in the integer.  The macro version
+ *             evaluates its argument multiple times.
+ */
+
+#define MPSCAN_RSTEP(m)                                                        \
+  ((m)->bits ? ((m)->w <<= 1, (m)->bits--, 1) :                                \
+   (m)->vl > (m)->v ? ((m)->w = *--(m)->vl,                            \
+                      (m)->bits = MPW_BITS - 1, 1) :                   \
+   0)
+
+extern int mpscan_rstep(mpscan */*m*/);
+
+/* --- @mpscan_rbit@ --- *
+ *
+ * Arguments:  @const mpscan *m@ = pointer to bitscanner
+ *
+ * Returns:    The value of the current bit.
+ *
+ * Use:                Reads the value of the current bit looked at by a
+ *             reverse bitscanner.
+ */
+
+#define MPSCAN_RBIT(m) (((m)->w >> (MPW_BITS - 1)) & 1)
+
+extern int mpscan_rbit(const mpscan */*m*/);
+
 /*----- That's all, folks -------------------------------------------------*/
 
 #ifdef __cplusplus