Let's try this. It's BUGGERED.

src/cmd/pic/for.c

@@ -0,0 +1,95 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include "pic.h"
+#include "y.tab.h"
+
+#define	SLOP	1.001
+
+typedef struct {
+	char	*var;	/* index variable */
+	double	to;	/* limit */
+	double	by;
+	int	op;	/* operator */
+	char	*str;	/* string to push back */
+} For;
+
+For	forstk[10];	/* stack of for loops */
+For	*forp = forstk;	/* pointer to current top */
+
+void	setfval(char *, double);
+void	nextfor(void);
+
+void forloop(char *var, double from, double to, int op,
+	double by, char *str)	/* set up a for loop */
+{
+	dprintf("# for %s from %g to %g by %c %g \n",
+		var, from, to, op, by);
+	if (++forp >= forstk+10)
+		ERROR "for loop nested too deep" FATAL;
+	forp->var = var;
+	forp->to = to;
+	forp->op = op;
+	forp->by = by;
+	forp->str = str;
+	setfval(var, from);
+	nextfor();
+	unput('\n');
+}
+
+void nextfor(void)	/* do one iteration of a for loop */
+{
+	/* BUG:  this should depend on op and direction */
+	if (getfval(forp->var) > SLOP * forp->to) {	/* loop is done */
+		free(forp->str);
+		if (--forp < forstk)
+			ERROR "forstk popped too far" FATAL;
+	} else {		/* another iteration */
+		pushsrc(String, "\nEndfor\n");
+		pushsrc(String, forp->str);
+	}
+}
+
+void endfor(void)	/* end one iteration of for loop */
+{
+	struct symtab *p = lookup(forp->var);
+
+	switch (forp->op) {
+	case '+':
+	case ' ':
+		p->s_val.f += forp->by;
+		break;
+	case '-':
+		p->s_val.f -= forp->by;
+		break;
+	case '*':
+		p->s_val.f *= forp->by;
+		break;
+	case '/':
+		p->s_val.f /= forp->by;
+		break;
+	}
+	nextfor();
+}
+
+char *ifstat(double expr, char *thenpart, char *elsepart)
+{
+	dprintf("if %g then <%s> else <%s>\n", expr, thenpart, elsepart? elsepart : "");
+	if (expr) {
+		unput('\n');
+		pushsrc(Free, thenpart);
+		pushsrc(String, thenpart);
+		unput('\n');
+  		if (elsepart)
+			free(elsepart);
+		return thenpart;	/* to be freed later */
+	} else {
+		free(thenpart);
+		if (elsepart) {
+			unput('\n');
+			pushsrc(Free, elsepart);
+			pushsrc(String, elsepart);
+			unput('\n');
+		}
+		return elsepart;
+	}
+}