X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/d34decd2b2b88240cf4ca68a2a5feb7bf36de6e7..4640a0dd947f422cfda780c62da342792af27b7b:/mpmont.c

diff --git a/mpmont.c b/mpmont.c
index e7b9bb7..2371de8 100644
--- a/mpmont.c
+++ b/mpmont.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: mpmont.c,v 1.9 2000/06/17 11:45:09 mdw Exp $
+ * $Id: mpmont.c,v 1.15 2001/06/16 13:00:20 mdw Exp $
  *
  * Montgomery reduction
  *
@@ -30,6 +30,27 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: mpmont.c,v $
+ * Revision 1.15  2001/06/16 13:00:20  mdw
+ * Use the generic exponentiation functions.
+ *
+ * Revision 1.14  2001/02/22 09:04:26  mdw
+ * Cosmetic fix.
+ *
+ * Revision 1.13  2001/02/03 12:00:29  mdw
+ * Now @mp_drop@ checks its argument is non-NULL before attempting to free
+ * it.  Note that the macro version @MP_DROP@ doesn't do this.
+ *
+ * Revision 1.12  2000/10/08 15:48:35  mdw
+ * Rename Karatsuba constants now that we have @gfx_kmul@ too.
+ *
+ * Revision 1.11  2000/10/08 12:04:27  mdw
+ * (mpmont_reduce, mpmont_mul): Cope with negative numbers.
+ *
+ * Revision 1.10  2000/07/29 17:05:43  mdw
+ * (mpmont_expr): Use sliding window exponentiation, with a drop-through
+ * for small exponents to use a simple left-to-right bitwise routine.  This
+ * can reduce modexp times by up to a quarter.
+ *
  * Revision 1.9  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
@@ -70,6 +91,7 @@
 
 #include "mp.h"
 #include "mpmont.h"
+#include "mpmont-exp.h"
 
 /*----- Tweakables --------------------------------------------------------*/
 
@@ -81,7 +103,7 @@
 
 /* #define MPMONT_DISABLE */
 
-/*----- Main code ---------------------------------------------------------*/
+/*----- Reduction and multiplication --------------------------------------*/
 
 /* --- @mpmont_create@ --- *
  *
@@ -190,7 +212,7 @@ mp *mpmont_reduce(mpmont *mm, mp *d, mp *a)
 
   /* --- Check for serious Karatsuba reduction --- */
 
-  if (n > KARATSUBA_CUTOFF * 3) {
+  if (n > MPK_THRESH * 3) {
     mp al;
     mpw *vl;
     mp *u;
@@ -241,8 +263,12 @@ mp *mpmont_reduce(mpmont *mm, mp *d, mp *a)
 
   memmove(d->v, d->v + n, MPWS(MP_LEN(d) - n));
   d->vl -= n;
-  if (MP_CMP(d, >=, mm->m))
-    d = mp_sub(d, d, mm->m);
+  if (MPX_UCMP(d->v, d->vl, >=, mm->m->v, mm->m->vl))
+    mpx_usub(d->v, d->vl, d->v, d->vl, mm->m->v, mm->m->vl);
+  if (d->f & MP_NEG) {
+    mpx_usub(d->v, d->vl, mm->m->v, mm->m->vl, d->v, d->vl);
+    d->f &= ~MP_NEG;
+  }
   MP_SHRINK(d);
   return (d);
 }
@@ -271,7 +297,7 @@ mp *mpmont_mul(mpmont *mm, mp *d, mp *a, mp *b)
 
 mp *mpmont_mul(mpmont *mm, mp *d, mp *a, mp *b)
 {
-  if (mm->n > KARATSUBA_CUTOFF * 3) {
+  if (mm->n > MPK_THRESH * 3) {
     d = mp_mul(d, a, b);
     d = mpmont_reduce(mm, d, d);
   } else {
@@ -326,10 +352,12 @@ mp *mpmont_mul(mpmont *mm, mp *d, mp *a, mp *b)
 
     memmove(d->v, dv, MPWS(dvl - dv));
     d->vl -= dv - d->v;
+    if (MPX_UCMP(d->v, d->vl, >=, mm->m->v, mm->m->vl))
+      mpx_usub(d->v, d->vl, d->v, d->vl, mm->m->v, mm->m->vl);
+    if ((a->f ^ b->f) & MP_NEG)
+      mpx_usub(d->v, d->vl, mm->m->v, mm->m->vl, d->v, d->vl);
     MP_SHRINK(d);
     d->f = (a->f | b->f) & MP_BURN;
-    if (MP_CMP(d, >=, mm->m))
-      d = mp_sub(d, d, mm->m);
     MP_DROP(a);
     MP_DROP(b);
   }
@@ -339,6 +367,8 @@ mp *mpmont_mul(mpmont *mm, mp *d, mp *a, mp *b)
 
 #endif
 
+/*----- Exponentiation ----------------------------------------------------*/
+
 /* --- @mpmont_expr@ --- *
  *
  * Arguments:	@mpmont *mm@ = pointer to Montgomery reduction context
@@ -346,42 +376,23 @@ mp *mpmont_mul(mpmont *mm, mp *d, mp *a, mp *b)
  *		@mp *a@ = base
  *		@mp *e@ = exponent
  *
- * Returns:	Result, %$a^e R \bmod m$%.
+ * Returns:	Result, %$(a R^{-1})^e R \bmod m$%.
  */
 
 mp *mpmont_expr(mpmont *mm, mp *d, mp *a, mp *e)
 {
-  mpscan sc;
-  mp *ar = mpmont_mul(mm, MP_NEW, a, mm->r2);
   mp *x = MP_COPY(mm->r);
   mp *spare = (e->f & MP_BURN) ? MP_NEWSEC : MP_NEW;
 
-  mp_scan(&sc, e);
-
-  if (MP_STEP(&sc)) {
-    size_t sq = 0;
-    for (;;) {
-      mp *dd;
-      if (MP_BIT(&sc)) {
-	while (sq) {
-	  dd = mp_sqr(spare, ar);
-	  dd = mpmont_reduce(mm, dd, dd);
-	  spare = ar; ar = dd;
-	  sq--;
-	}
-	dd = mpmont_mul(mm, spare, x, ar);
-	spare = x; x = dd;
-      }
-      sq++;
-      if (!MP_STEP(&sc))
-	break;
-    }
-  }
-  MP_DROP(ar);
-  if (spare != MP_NEW)
-    MP_DROP(spare);
-  if (d != MP_NEW)
-    MP_DROP(d);
+  MP_SHRINK(e);
+  if (MP_LEN(e) == 0)
+    ;
+  else if (MP_LEN(e) < EXP_THRESH)
+    EXP_SIMPLE(x, a, e);
+  else
+    EXP_WINDOW(x, a, e);
+  mp_drop(d);
+  mp_drop(spare);
   return (x);
 }
 
@@ -397,7 +408,8 @@ mp *mpmont_expr(mpmont *mm, mp *d, mp *a, mp *e)
 
 mp *mpmont_exp(mpmont *mm, mp *d, mp *a, mp *e)
 {
-  d = mpmont_expr(mm, d, a, e);
+  d = mpmont_mul(mm, d, a, mm->r2);
+  d = mpmont_expr(mm, d, d, e);
   d = mpmont_reduce(mm, d, d);
   return (d);
 }
@@ -426,7 +438,7 @@ static int tcreate(dstr *v)
     ok = 0;
   }
 
-  if (MP_CMP(mm.r, !=, r)) {
+  if (!MP_EQ(mm.r, r)) {
     fputs("\n*** bad r", stderr);
     fputs("\nm = ", stderr); mp_writefile(m, stderr, 10);
     fputs("\nexpected ", stderr); mp_writefile(r, stderr, 10);
@@ -435,7 +447,7 @@ static int tcreate(dstr *v)
     ok = 0;
   }
 
-  if (MP_CMP(mm.r2, !=, r2)) {
+  if (!MP_EQ(mm.r2, r2)) {
     fputs("\n*** bad r2", stderr);
     fputs("\nm = ", stderr); mp_writefile(m, stderr, 10);
     fputs("\nexpected ", stderr); mp_writefile(r2, stderr, 10);
@@ -468,7 +480,7 @@ static int tmul(dstr *v)
     mp *qr = mp_mul(MP_NEW, a, b);
     mp_div(0, &qr, qr, m);
 
-    if (MP_CMP(qr, !=, r)) {
+    if (!MP_EQ(qr, r)) {
       fputs("\n*** classical modmul failed", stderr);
       fputs("\n m = ", stderr); mp_writefile(m, stderr, 10);
       fputs("\n a = ", stderr); mp_writefile(a, stderr, 10);
@@ -487,7 +499,7 @@ static int tmul(dstr *v)
     mp *br = mpmont_mul(&mm, MP_NEW, b, mm.r2);
     mp *mr = mpmont_mul(&mm, MP_NEW, ar, br);
     mr = mpmont_reduce(&mm, mr, mr);
-    if (MP_CMP(mr, !=, r)) {
+    if (!MP_EQ(mr, r)) {
       fputs("\n*** montgomery modmul failed", stderr);
       fputs("\n m = ", stderr); mp_writefile(m, stderr, 10);
       fputs("\n a = ", stderr); mp_writefile(a, stderr, 10);
@@ -525,7 +537,7 @@ static int texp(dstr *v)
 
   mr = mpmont_exp(&mm, MP_NEW, a, b);
 
-  if (MP_CMP(mr, !=, r)) {
+  if (!MP_EQ(mr, r)) {
     fputs("\n*** montgomery modexp failed", stderr);
     fputs("\n m = ", stderr); mp_writefile(m, stderr, 10);
     fputs("\n a = ", stderr); mp_writefile(a, stderr, 10);