Fix LOOP/+LOOP bug.

Forth-83 and after pick a more useful definition of how
LOOP and +LOOP should decide termination:
if the last step traversed between limit-1 and limit.

This allows for signed or unsigned loops with the same construct.

Updating to this behavior + adding test + fixing old test
that didn't match gforth.

common/boot.fs

@@ -69,10 +69,12 @@ variable leaving
 : UNLOOP   r> rdrop rdrop >r ;
 : LEAVE   r> rdrop rdrop @ >r ;
 : leave   postpone LEAVE leaving, ; immediate
-: +LOOP ( n -- ) dup 0< swap r> r> rot + dup r@ < -rot >r >r xor 0=
+: +LOOP ( n -- ) r> r> dup r@ - >r rot + r> -rot
+                       dup r@ - -rot >r >r xor 0<
                  if r> cell+ rdrop rdrop >r else r> @ >r then ;
 : +loop ( n -- ) postpone +LOOP , )leaving ; immediate
-: LOOP   r> r> 1+ dup r@ < -rot >r >r 0=
+: LOOP   r> r> dup r@ - >r 1+ r> -rot
+               dup r@ - -rot >r >r xor 0<
          if r> cell+ rdrop rdrop >r else r> @ >r then ;
 : loop   postpone LOOP , )leaving ; immediate
 create I ' r@ @ ' i !  ( i is same as r@ )

common/doloop_tests.fs

@@ -42,74 +42,74 @@ e: test-rev-?doloop
 
 e: test-do+loop
   : foo 0 do i . 2 +loop cr ;
-  9 foo
+  ." 9 foo " 9 foo
-  out: 0 2 4 6 8 
+  out: 9 foo 0 2 4 6 8 
-  10 foo
+  ." 10 foo " 10 foo
-  out: 0 2 4 6 8 
+  out: 10 foo 0 2 4 6 8 
-  11 foo
+  ." 11 foo " 11 foo
-  out: 0 2 4 6 8 10 
+  out: 11 foo 0 2 4 6 8 10 
-  1 foo
+  ." 1 foo " 1 foo
-  out: 0 
+  out: 1 foo 0 
 ;e
 
 e: test-?do+loop
   : foo 0 ?do i . 2 +loop cr ;
-  9 foo
+  ." 9 foo " 9 foo
-  out: 0 2 4 6 8 
+  out: 9 foo 0 2 4 6 8 
-  10 foo
+  ." 10 foo " 10 foo
-  out: 0 2 4 6 8 
+  out: 10 foo 0 2 4 6 8 
-  11 foo
+  ." 11 foo " 11 foo
-  out: 0 2 4 6 8 10 
+  out: 11 foo 0 2 4 6 8 10 
-  1 foo
+  ." 1 foo " 1 foo
-  out: 0 
+  out: 1 foo 0 
-  0 foo
+  ." 0 foo " 0 foo
-  out: 
+  out: 0 foo 
 ;e
 
 e: test-doloop-leave
   : foo 0 do 42 emit i 7 = if ." left " leave ." nope" then i . loop cr ;
-  7 foo
+  ." 7 foo " 7 foo
-  out: *0 *1 *2 *3 *4 *5 *6 
+  out: 7 foo *0 *1 *2 *3 *4 *5 *6 
-  8 foo
+  ." 8 foo " 8 foo
-  out: *0 *1 *2 *3 *4 *5 *6 *left 
+  out: 8 foo *0 *1 *2 *3 *4 *5 *6 *left 
-  9 foo
+  ." 9 foo " 9 foo
-  out: *0 *1 *2 *3 *4 *5 *6 *left 
+  out: 9 foo *0 *1 *2 *3 *4 *5 *6 *left 
 ;e
 
 e: test-do+loop-leave
   : foo 0 do 42 emit i 8 = if ." left " leave ." nope" then i . 2 +loop cr ;
-  7 foo
+  ." 7 foo " 7 foo
-  out: *0 *2 *4 *6 
+  out: 7 foo *0 *2 *4 *6 
-  8 foo
+  ." 8 foo " 8 foo
-  out: *0 *2 *4 *6 
+  out: 8 foo *0 *2 *4 *6 
-  9 foo
+  ." 9 foo " 9 foo
-  out: *0 *2 *4 *6 *left 
+  out: 9 foo *0 *2 *4 *6 *left 
-  0 foo
+  ." 0 foo " 0 foo
-  out: *0 
+  out: 0 foo *0 *2 *4 *6 *left 
 ;e
 
 e: test-?do+loop-leave
   : foo 0 ?do 42 emit i 8 = if ." left " leave ." nope" then i . 2 +loop cr ;
-  7 foo
+  ." 7 foo " 7 foo
-  out: *0 *2 *4 *6 
+  out: 7 foo *0 *2 *4 *6 
-  8 foo
+  ." 8 foo " 8 foo
-  out: *0 *2 *4 *6 
+  out: 8 foo *0 *2 *4 *6 
-  9 foo
+  ." 9 foo " 9 foo
-  out: *0 *2 *4 *6 *left 
+  out: 9 foo *0 *2 *4 *6 *left 
-  0 foo
+  ." 0 foo " 0 foo
-  out: 
+  out: 0 foo 
 ;e
 
 e: test-do+loop-unloop
   : foo 0 do 42 emit i 8 = if ." left " cr unloop exit then i . 2 +loop ." done " cr ;
-  7 foo
+  ." 7 foo " 7 foo
-  out: *0 *2 *4 *6 done 
+  out: 7 foo *0 *2 *4 *6 done 
-  8 foo
+  ." 8 foo " 8 foo
-  out: *0 *2 *4 *6 done 
+  out: 8 foo *0 *2 *4 *6 done 
-  9 foo
+  ." 9 foo " 9 foo
-  out: *0 *2 *4 *6 *left 
+  out: 9 foo *0 *2 *4 *6 *left 
-  0 foo
+  ." 0 foo " 0 foo
-  out: *0 done 
+  out: 0 foo *0 *2 *4 *6 *left 
 ;e
 
 e: test-?do+loop-unloop
@@ -130,3 +130,14 @@ e: test-doloop-j
   out: 0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 
 ;e
 
+e: test-doloop-unsigned
+  : foo 0 -1 1 rshift 1+ dup 10 + swap do 1+ loop . cr ;
+  foo
+  out: 10 
+;e
+
+e: test-do+loop-unsigned
+  : foo 0 -1 1 rshift dup 10 + do 1+ -1 +loop . cr ;
+  foo
+  out: 11 
+;e