Fix @mp_lsl2c@. Turns out to be surprisingly tricky.

[u/mdw/catacomb] / mp-arith.c

diff --git a/mp-arith.c b/mp-arith.c
index 759056b..3d565ae 100644 (file)
--- a/mp-arith.c
+++ b/mp-arith.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: mp-arith.c,v 1.15 2002/10/19 17:56:50 mdw Exp $
+ * $Id: mp-arith.c,v 1.16 2003/05/16 09:09:24 mdw Exp $
  *
  * Basic arithmetic on multiprecision integers
  *
@@ -30,6 +30,9 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: mp-arith.c,v $
+ * Revision 1.16  2003/05/16 09:09:24  mdw
+ * Fix @mp_lsl2c@.  Turns out to be surprisingly tricky.
+ *
  * Revision 1.15  2002/10/19 17:56:50  mdw
  * Fix bit operations.  Test them (a bit) better.
  *
@@ -91,13 +94,18 @@
 
 /*----- Main code ---------------------------------------------------------*/
 
-/* --- @mp_lsl@, @mp_lsr@ --- *
+/* --- @mp_lsl@, @mp_lslc@, @mp_lsr@ --- *
  *
  * Arguments:  @mp *d@ = destination
  *             @mp *a@ = source
  *             @size_t n@ = number of bits to move
  *
  * Returns:    Result, @a@ shifted left or right by @n@.
+ *
+ * Use:                Bitwise shift operators.  @mp_lslc@ fills the bits introduced
+ *             on the right with ones instead of zeroes: it's used
+ *             internally by @mp_lsl2c@, though it may be useful on its
+ *             own.
  */
 
 mp *mp_lsl(mp *d, mp *a, size_t n)
@@ -109,6 +117,15 @@ mp *mp_lsl(mp *d, mp *a, size_t n)
   return (d);
 }
 
+mp *mp_lslc(mp *d, mp *a, size_t n)
+{
+  MP_DEST(d, MP_LEN(a) + (n + MPW_BITS - 1) / MPW_BITS, a->f);
+  mpx_lslc(d->v, d->vl, a->v, a->vl, n);
+  d->f = a->f & (MP_NEG | MP_BURN);
+  MP_SHRINK(d);
+  return (d);
+}
+
 mp *mp_lsr(mp *d, mp *a, size_t n)
 {
   MP_DEST(d, MP_LEN(a), a->f);
@@ -133,7 +150,7 @@ mp *mp_lsl2c(mp *d, mp *a, size_t n)
   if (!(a->f & MP_NEG))
     return (mp_lsl(d, a, n));
   d = mp_not2c(d, a);
-  d = mp_lsl(d, d, n);
+  d = mp_lslc(d, d, n);
   d = mp_not2c(d, d);
   return (d);
 }
@@ -293,10 +310,10 @@ mp *mp_neg(mp *d, mp *a)
 
   MP_SHRINK(a);
   MP_COPY(a);
-  if (d) MP_DROP(d);
-  if (a->v == a->vl) {
+  if (d)
+    MP_DROP(d);
+  if (a->v == a->vl)
     return (a);
-  }
   MP_DEST(a, MP_LEN(a), a->f);
   a->f ^= MP_NEG;
   return (a);