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pc: add cat() function

--- 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 cat(a0,n0,...,aN,nN)

+Truncate each of the \fIa\fR arguments to \fIn\fR bits and concatenate their binary representation.

+.TP

 .I gcd(n,m)

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

 .TP

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

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

@@ -836,6 +836,36 @@

 	return a[0];

 }

+Num *

+fncat(int n, Num **a)

+{

+	int i, w;

+	Num *r;

+

+	if(n % 2 != 0){

+		error("cat: odd number of arguments");

+		i = 0;

+	fail:

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

+			numdecref(a[i]);

+		return nil;

+	}

+	r = numalloc();

+	for(i = 0; i < n; i += 2){

+		if(toint(a[i+1], &w, 1)) goto fail;

+		mpleft(r, w, r);

+		if(a[i]->sign < 0 || mpsignif(a[i]) > w){

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

+			mptrunc(a[i], w, a[i]);

+		}

+		r->b = basemax(r->b, a[i]->b);

+		mpor(r, a[i], r);

+		numdecref(a[i]);

+		numdecref(a[i+1]);

+	}

+	return r;

+}

+

 void

 main(int argc, char **argv)

 {

@@ -863,6 +893,7 @@

 	regfunc("minv", fnminv, 2);

 	regfunc("rand", fnrand, 1);

 	regfunc("rev", fnrev, 2);

+	regfunc("cat", fncat, -1);

 	prompt = 1;

 	ARGBEGIN{