Why not?

src/cmd/map/libmap/aitoff.c

@@ -0,0 +1,26 @@
+#include <u.h>
+#include <libc.h>
+#include "map.h"
+
+#define Xaitwist Xaitpole.nlat
+static struct place Xaitpole;
+
+static int
+Xaitoff(struct place *place, double *x, double *y)
+{
+	struct place p;
+	copyplace(place,&p);
+	p.wlon.l /= 2.;
+	sincos(&p.wlon);
+	norm(&p,&Xaitpole,&Xaitwist);
+	Xazequalarea(&p,x,y);
+	*x *= 2.;
+	return(1);
+}
+
+proj
+aitoff(void)
+{
+	latlon(0.,0.,&Xaitpole);
+	return(Xaitoff);
+}