libmp: allow passing nil to v,x,y results of mpextendedgcd(), simplify mpinvert()

2 files changed, 14 insertions, 12 deletions

diff --git a/sys/src/libmp/port/mpextendedgcd.c b/sys/src/libmp/port/mpextendedgcd.c
index 72e49bce1..562c85a1c 100644
--- a/sys/src/libmp/port/mpextendedgcd.c
+++ b/sys/src/libmp/port/mpextendedgcd.c
@@ -15,8 +15,16 @@ mpextendedgcd(mpint *a, mpint *b, mpint *v, mpint *x, mpint *y)
 	mpint *u, *A, *B, *C, *D;
 	int g;
 
+	if(v == nil){
+		v = mpnew(0);
+		mpextendedgcd(a, b, v, x, y);
+		mpfree(v);
+		return;
+	}
+	assert(x == nil || (x->flags & MPtimesafe) == 0);
+	assert(y == nil || (y->flags & MPtimesafe) == 0);
 	assert((a->flags&b->flags) & MPnorm);
-	assert(((a->flags|b->flags|v->flags|x->flags|y->flags) & MPtimesafe) == 0);
+	assert(((a->flags|b->flags|v->flags) & MPtimesafe) == 0);
 
 	if(a->sign < 0 || b->sign < 0){
 		mpassign(mpzero, v);
@@ -104,6 +112,4 @@ mpextendedgcd(mpint *a, mpint *b, mpint *v, mpint *x, mpint *y)
 	mpfree(u);
 	mpfree(a);
 	mpfree(b);
-
-	return;
 }
diff --git a/sys/src/libmp/port/mpinvert.c b/sys/src/libmp/port/mpinvert.c
index ee2630702..59713747b 100644
--- a/sys/src/libmp/port/mpinvert.c
+++ b/sys/src/libmp/port/mpinvert.c
@@ -1,21 +1,17 @@
 #include "os.h"
 #include <mp.h>
 
-#define iseven(a)	(((a)->p[0] & 1) == 0)
-
 // use extended gcd to find the multiplicative inverse
 // res = b**-1 mod m
 void
 mpinvert(mpint *b, mpint *m, mpint *res)
 {
-	mpint *dc1, *dc2;	// don't care
+	mpint *v;
 
-	dc1 = mpnew(0);
-	dc2 = mpnew(0);
-	mpextendedgcd(b, m, dc1, res, dc2);
-	if(mpcmp(dc1, mpone) != 0)
+	v = mpnew(0);
+	mpextendedgcd(b, m, v, res, nil);
+	if(mpcmp(v, mpone) != 0)
 		abort();
+	mpfree(v);
 	mpmod(res, m, res);
-	mpfree(dc1);
-	mpfree(dc2);
 }