filled-in gaps in string memory release routine

src/basic/basic_commands/cmd_let.s

@@ -171,12 +171,10 @@ cmd_let_assign_string:
 	lda __FAC1+0
 	bne cmd_let_assign_string_not_empty
 
-	// Yes, it is empty - check if the old one is, free it if necessary
+	// Yes, it is empty - free the old one
 
-	lda DSCPNT+0
-	bne !+
 	jsr varstr_free
-!:
+
 	// Set the new variable as empty string
 
 	ldy #$00
@@ -276,9 +274,7 @@ cmd_let_assign_string_not_text_area:
 	// No special case optimization is possible
 	// Free the memory belonging to the old string
 
-	// XXX
-	// jsr varstr_free
-
+	jsr varstr_free
 
 	// And allocate memory for the new string
 

src/basic/engine/varstr_cmp_fretop.s

@@ -0,0 +1,23 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# *   BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+//
+// Check string address (DSCPNT+1/+2) vs FRETOP
+//
+// Output:
+// - Zero flag set  - this is the first variable of the string area
+// - Carry flag set - this string belongs to the string area
+
+
+varstr_cmp_fretop:
+
+	lda DSCPNT+2
+	cmp FRETOP+1
+	beq !+
+	rts
+!:
+	lda DSCPNT+2
+	cmp FRETOP+1
+	rts
+

src/basic/engine/varstr_free.s

@@ -6,27 +6,32 @@
 // Releases back memory used by string
 //
 // Input:
+// - DSCPNT+0           - string size
 // - DSCPNT+1, DSCPNT+2 - pointer to string
 //
 
 // XXX test this routine
-// XXX check if this entry point is needed
 
 
 varstr_free:
 
-	// XXX consider moving size check (DSCPNT+0) here
+	// Check the string size - do not do anything if 0
 
-	// XXX
-	// XXX check if string is located above FRETOP, handle case if it is not
-	// XXX
+	lda DSCPNT+0
+	bne !+
+	rts
+!:
+	// Check if string is above FRETOP (in string area)
 
-	// Quick check - is the string the lowest one?
+	jsr varstr_cmp_fretop
+	bcs !+
+
+	// No, it does not belong to string area - quit
+
+	rts
+!:
+	// Check if this is the lowest string
 
-	cmp FRETOP+0
-	bne varstr_free_inside
-	lda DSCPNT+2
-	cmp FRETOP+1
 	bne varstr_free_inside
 
 	// This is the lowest string - so just increase FRETOP, this way