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pc(1): fix memory leak and add clog() function

--- a/sys/man/1/pc

+++ b/sys/man/1/pc

@@ -105,6 +105,9 @@

 .I gcd(n,m)

 The greatest common divisor of \fIn\fR and \fIm\fR.

 .TP

+.I clog(a,b)

+The ceiling of the logarithm of \fIa\fR with respect to base \fIb\fR. \fIb\fR can be omitted, in which case it defaults to 2.

+.TP

 .I minv(n,m)

 The inverse of \fIn\fR mod \fIm\fR.

 .TP

--- a/sys/src/cmd/pc.y

+++ b/sys/src/cmd/pc.y

@@ -310,15 +310,28 @@

 	free(t);

 }

+void

+numdecrefs(int n, Num **x)

+{

+	int i;

+	

+	for(i = 0; i < n; i++)

+		numdecref(x[i]);

+}

+

 Num *

 fncall(Symbol *s, int n, Num **x)

 {

 	int i;

-	if(s->t != SYMFUNC)

+	if(s->t != SYMFUNC){

+		numdecrefs(n, x);

 		return error("%s: not a function", s->name);

-	else if(s->nargs >= 0 && s->nargs != n)

+	}

+	else if(s->nargs >= 0 && s->nargs != n){

+		numdecrefs(n, x);

 		return error("%s: wrong number of arguments", s->name);

+	}

 	for(i = 0; i < n; i++)

 		if(x[i] == nil)

 			return nil;

@@ -820,6 +833,39 @@

 }

 Num *

+fnclog(int n, Num **a)

+{

+	int r;

+

+	if(n != 1 && n != 2){

+		numdecrefs(n, a);

+		return error("clog: wrong number of arguments");

+	}

+	if(mpcmp(a[0], mpzero) <= 0 || n == 2 && mpcmp(a[1], mpone) <= 0){

+		numdecref(a[0]);

+		return error("invalid argument");

+	}

+	if(n == 1 || mpcmp(a[1], mptwo) == 0){

+		a[0] = nummod(a[0]);

+		mpsub(a[0], mpone, a[0]);

+		itomp(mpsignif(a[0]), a[0]);

+		a[0]->b = 0;

+		if(n == 2) numdecref(a[1]);

+		return a[0];

+	}

+	a[0] = nummod(a[0]);

+	for(r = 0; mpcmp(a[0], mpone) > 0; r++){

+		mpadd(a[0], a[1], a[0]);

+		mpsub(a[0], mpone, a[0]);

+		mpdiv(a[0], a[1], a[0], nil);

+	}

+	itomp(r, a[0]);

+	a[0]->b = 0;

+	numdecref(a[1]);

+	return a[0];

+}

+

+Num *

 fnubits(int, Num **a)

 {

 	if(a[0]->sign < 0){

@@ -986,6 +1032,7 @@

 	regfunc("ceil", fnceil, 2);

 	regfunc("trunc", fntrunc, 2);

 	regfunc("xtend", fnxtend, 2);

+	regfunc("clog", fnclog, -1);

 	regfunc("ubits", fnubits, 1);

 	regfunc("sbits", fnsbits, 1);

 	regfunc("nsa", fnnsa, 1);