gitignore fix

cairo/.gitignore

@@ -157,4 +157,6 @@ cython_debug/
 #  be found at https://github.com/github/gitignore/blob/main/Global/JetBrains.gitignore
 #  and can be added to the global gitignore or merged into this file.  For a more nuclear
 #  option (not recommended) you can uncomment the following to ignore the entire idea folder.
-#.idea/
+#.idea/
+
+!/lang/compiler/lib/

cairo/lang/compiler/lib/registers.cairo

@@ -0,0 +1,18 @@
+// Returns the contents of the fp and pc registers of the calling function.
+// The pc register's value is the address of the instruction that follows directly after the
+// invocation of get_fp_and_pc().
+func get_fp_and_pc() -> (fp_val: felt*, pc_val: felt*) {
+    // The call instruction itself already places the old fp and the return pc at
+    // [ap - 2], [ap - 1].
+    return (fp_val=cast([ap - 2], felt*), pc_val=cast([ap - 1], felt*));
+}
+
+// Returns the content of the ap register just before this function was invoked.
+@known_ap_change
+func get_ap() -> (ap_val: felt*) {
+    // Once get_ap() is invoked, fp points to ap + 2 (since the call instruction placed the old fp
+    // and pc in memory, advancing ap accordingly).
+    // Hence, the desired ap value is fp - 2.
+    let (fp_val, pc_val) = get_fp_and_pc();
+    return (ap_val=fp_val - 2);
+}