6.1.0140
+LOOP
plus-loop
CORE
Interpretation:
Interpretation semantics for this word are undefined.

Compilation:
( C: do-sys -- )

Append the run-time semantics given below to the current definition. Resolve the destination of all unresolved occurrences of LEAVE between the location given by do-sys and the next location for a transfer of control, to execute the words following +LOOP.

Run-time:
( n -- ) ( R: loop-sys1 -- | loop-sys2 )

An ambiguous condition exists if the loop control parameters are unavailable. Add n to the loop index. If the loop index did not cross the boundary between the loop limit minus one and the loop limit, continue execution at the beginning of the loop. Otherwise, discard the current loop control parameters and continue execution immediately following the loop.

See:
6.1.1240 DO, 6.1.1680 I, 6.1.1760 LEAVE, A.6.1.0140 +LOOP.

Rationale:
Typical use: : X ... limit first DO ... step +LOOP ;
Testing:
T{ : GD2 DO I -1 +LOOP ; -> }T
T{        1          4 GD2 -> 4 3 2  1 }T
T{       -1          2 GD2 -> 2 1 0 -1 }T
T{ MID-UINT MID-UINT+1 GD2 -> MID-UINT+1 MID-UINT }T

VARIABLE gditerations
VARIABLE gdincrement

: gd7 ( limit start increment -- )
   gdincrement !
   0 gditerations !
   DO
     1 gditerations +!
     I
     gditerations @ 6 = IF LEAVE THEN
     gdincrement @
   +LOOP gditerations @
;

T{    4  4  -1 gd7 ->  4                  1  }T
T{    1  4  -1 gd7 ->  4  3  2  1         4  }T
T{    4  1  -1 gd7 ->  1  0 -1 -2  -3  -4 6  }T
T{    4  1   0 gd7 ->  1  1  1  1   1   1 6  }T
T{    0  0   0 gd7 ->  0  0  0  0   0   0 6  }T
T{    1  4   0 gd7 ->  4  4  4  4   4   4 6  }T
T{    1  4   1 gd7 ->  4  5  6  7   8   9 6  }T
T{    4  1   1 gd7 ->  1  2  3            3  }T
T{    4  4   1 gd7 ->  4  5  6  7   8   9 6  }T
T{    2 -1  -1 gd7 -> -1 -2 -3 -4  -5  -6 6  }T
T{   -1  2  -1 gd7 ->  2  1  0 -1         4  }T
T{    2 -1   0 gd7 -> -1 -1 -1 -1  -1  -1 6  }T
T{   -1  2   0 gd7 ->  2  2  2  2   2   2 6  }T
T{   -1  2   1 gd7 ->  2  3  4  5   6   7 6  }T
T{    2 -1   1 gd7 -> -1 0 1              3  }T
T{  -20 30 -10 gd7 -> 30 20 10  0 -10 -20 6  }T
T{  -20 31 -10 gd7 -> 31 21 11  1  -9 -19 6  }T
T{  -20 29 -10 gd7 -> 29 19  9 -1 -11     5  }T

\ With large and small increments

MAX-UINT 8 RSHIFT 1+ CONSTANT ustep
ustep NEGATE CONSTANT -ustep
MAX-INT 7 RSHIFT 1+ CONSTANT step
step NEGATE CONSTANT -step

VARIABLE bump

T{  : gd8 bump ! DO 1+ bump @ +LOOP ; -> }T

T{  0 MAX-UINT 0 ustep gd8 -> 256 }T
T{  0 0 MAX-UINT -ustep gd8 -> 256 }T
T{  0 MAX-INT MIN-INT step gd8 -> 256 }T
T{  0 MIN-INT MAX-INT -step gd8 -> 256 }T