pc(1): add nsa() command

sys/man/1/pc

@@ -93,6 +93,9 @@ The minimum number of bits required to represent \fIn\fR as an unsigned number.
 .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

sys/src/cmd/pc.y

@@ -766,6 +766,28 @@ fnsbits(int, Num **a)
 	return a[0];
 }
 
+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)
 {
@@ -889,6 +911,7 @@ main(int argc, char **argv)
 	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);