libmp: add mpfield() function for fast field arithmetic

instead of testing for special field primes each time in mpmod(),
make it explicit with a mpfiled() function that tests a modulus N
to be of some special form that can be reduced more efficiently with
some precalculation, and replaces N with a Mfield* when it can. the
Mfield*'s are recognized by mpmod() as they have the MPfield flag
set and provide a function pointer that executes the fast reduction.

1 files changed, 2 insertions, 2 deletions

diff --git a/sys/src/libmp/port/mpaux.c b/sys/src/libmp/port/mpaux.c
index eb70a9364..f85e782a9 100644
--- a/sys/src/libmp/port/mpaux.c
+++ b/sys/src/libmp/port/mpaux.c
@@ -137,7 +137,7 @@ mpcopy(mpint *old)
 	setmalloctag(new, getcallerpc(&old));
 	new->sign = old->sign;
 	new->top = old->top;
-	new->flags = old->flags & ~MPstatic;
+	new->flags = old->flags & ~(MPstatic|MPfield);
 	memmove(new->p, old->p, Dbytes*old->top);
 	return new;
 }
@@ -152,7 +152,7 @@ mpassign(mpint *old, mpint *new)
 	new->sign = old->sign;
 	new->top = old->top;
 	new->flags &= ~MPnorm;
-	new->flags |= old->flags & ~MPstatic;
+	new->flags |= old->flags & ~(MPstatic|MPfield);
 	memmove(new->p, old->p, Dbytes*old->top);
 }