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pc(1): add nsa() command

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

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

@@ -93,6 +93,9 @@

 .I sbits(n)

 The minimum number of bits required to represent \fIn\fR as an signed number.

 .TP

+.I nsa(n)

+The number of bits set in \fIn\fR.

+.TP

 .I cat(a\d\s70\s0\u,n\d\s70\s0\u,...,a\d\s7N\s0\u,n\d\s7N\s0\u)

 Truncate each of the \fIa\d\s7i\s0\u\fR arguments to \fIn\d\s7i\s0\u\fR bits and concatenate their binary representation.

 .TP

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

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

@@ -767,6 +767,28 @@

 }

 Num *

+fnnsa(int, Num **a)

+{

+	int n, i;

+	mpdigit d;

+

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

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

+		numdecref(a[0]);

+		return error("invalid argument");

+	}

+	n = 0;

+	for(i = 0; i < a[0]->top; i++){

+		d = a[0]->p[i];

+		for(; d != 0; d &= d-1)

+			n++;

+	}

+	itomp(n, a[0]);

+	a[0]->b = 0;

+	return a[0];

+}

+

+Num *

 fngcd(int, Num **a)

 {

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

@@ -889,6 +911,7 @@

 	regfunc("xtend", fnxtend, 2);

 	regfunc("ubits", fnubits, 1);

 	regfunc("sbits", fnsbits, 1);

+	regfunc("nsa", fnnsa, 1);

 	regfunc("gcd", fngcd, 2);

 	regfunc("minv", fnminv, 2);

 	regfunc("rand", fnrand, 1);