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ref: cc706364d052347dcf45ca6dabe9a92978ad6b11
parent: 90baca8302fd8b6ccad7d06b61da9ecf451ccf83
author: cinap_lenrek <cinap_lenrek@felloff.net>
date: Sun Aug 28 20:12:42 EDT 2016

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

--- a/libmp/mpextendedgcd.c	Sun Aug 28 18:46:51 2016
+++ b/libmp/mpextendedgcd.c	Sun Aug 28 20:12:42 2016
@@ -15,8 +15,16 @@
 	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 @@
 	mpfree(u);
 	mpfree(a);
 	mpfree(b);
-
-	return;
 }
--- a/libmp/mpinvert.c	Sun Aug 28 18:46:51 2016
+++ b/libmp/mpinvert.c	Sun Aug 28 20:12:42 2016
@@ -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);
 }