Implement efficient reduction for pleasant-looking primes.

[u/mdw/catacomb] / mpx.c

diff --git a/mpx.c b/mpx.c
index f40d7d9..f1cbbd9 100644 (file)
--- a/mpx.c
+++ b/mpx.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: mpx.c,v 1.16 2003/05/16 09:09:24 mdw Exp $
+ * $Id: mpx.c,v 1.17 2004/03/27 00:04:46 mdw Exp $
  *
  * Low-level multiprecision arithmetic
  *
@@ -30,6 +30,9 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: mpx.c,v $
+ * Revision 1.17  2004/03/27 00:04:46  mdw
+ * Implement efficient reduction for pleasant-looking primes.
+ *
  * Revision 1.16  2003/05/16 09:09:24  mdw
  * Fix @mp_lsl2c@.  Turns out to be surprisingly tricky.
  *
@@ -877,6 +880,30 @@ void mpx_uadd(mpw *dv, mpw *dvl, const mpw *av, const mpw *avl,
 
 void mpx_uaddn(mpw *dv, mpw *dvl, mpw n) { MPX_UADDN(dv, dvl, n); }
 
+/* --- @mpx_uaddnlsl@ --- *
+ *
+ * Arguments:  @mpw *dv, *dvl@ = destination and first argument vector
+ *             @mpw a@ = second argument
+ *             @unsigned o@ = offset in bits
+ *
+ * Returns:    ---
+ *
+ * Use:                Computes %$d + 2^o a$%.  If the result overflows then
+ *             high-order bits are discarded, as usual.  We must have
+ *             @0 < o < MPW_BITS@.
+ */
+
+void mpx_uaddnlsl(mpw *dv, mpw *dvl, mpw a, unsigned o)
+{
+  mpd x = (mpd)a << o;
+
+  while (x && dv < dvl) {
+    x += *dv;
+    *dv++ = MPW(x);
+    x >>= MPW_BITS;
+  }
+}
+
 /* --- @mpx_usub@ --- *
  *
  * Arguments:  @mpw *dv, *dvl@ = destination vector base and limit
@@ -931,6 +958,33 @@ void mpx_usub(mpw *dv, mpw *dvl, const mpw *av, const mpw *avl,
 
 void mpx_usubn(mpw *dv, mpw *dvl, mpw n) { MPX_USUBN(dv, dvl, n); }
 
+/* --- @mpx_uaddnlsl@ --- *
+ *
+ * Arguments:  @mpw *dv, *dvl@ = destination and first argument vector
+ *             @mpw a@ = second argument
+ *             @unsigned o@ = offset in bits
+ *
+ * Returns:    ---
+ *
+ * Use:                Computes %$d + 2^o a$%.  If the result overflows then
+ *             high-order bits are discarded, as usual.  We must have
+ *             @0 < o < MPW_BITS@.
+ */
+
+void mpx_usubnlsl(mpw *dv, mpw *dvl, mpw a, unsigned o)
+{
+  mpw b = a >> (MPW_BITS - o);
+  a <<= o;
+
+  if (dv < dvl) {
+    mpd x = (mpd)*dv - (mpd)a;
+    *dv++ = MPW(x);
+    if (x >> MPW_BITS)
+      b++;
+    MPX_USUBN(dv, dvl, b);
+  }
+}
+
 /* --- @mpx_umul@ --- *
  *
  * Arguments:  @mpw *dv, *dvl@ = destination vector base and limit