git @ Cat's Eye Technologies SixtyPical / 15fa488
Add some more tests (failing currently). Chris Pressey 3 years ago
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tests/SixtyPical Analysis.md less more
532532
533533 #### tables: range checking ####
534534
535 If a table has fewer than 256 entries, it cannot be read or written
536 beyond the maximum number of entries it has.
535 It is a static analysis error if it cannot be proven that a read or write
536 to a table falls within the defined size of that table.
537
538 (If a table has 256 entries, then there is never a problem, because a byte
539 cannot index any entry outside of 0..255.)
540
541 A SixtyPical implementation must be able to prove that the index is inside
542 the range of the table in various ways. The simplest is to show that a
543 constant value falls inside or outside the range of the table.
537544
538545 | byte table[32] many
539546 |
570577 | ld x, 32
571578 | ld a, 0
572579 | st a, many + x
580 | }
581 ? RangeExceededError
582
583 This applies to `copy` as well.
584
585 | word one: 77
586 | word table[32] many
587 |
588 | routine main
589 | inputs many, one
590 | outputs many, one
591 | trashes a, x, n, z
592 | {
593 | ld x, 31
594 | copy one, many + x
595 | copy many + x, one
596 | }
597 = ok
598
599 | word one: 77
600 | word table[32] many
601 |
602 | routine main
603 | inputs many, one
604 | outputs many, one
605 | trashes a, x, n, z
606 | {
607 | ld x, 32
608 | copy many + x, one
609 | }
610 ? RangeExceededError
611
612 | word one: 77
613 | word table[32] many
614 |
615 | routine main
616 | inputs many, one
617 | outputs many, one
618 | trashes a, x, n, z
619 | {
620 | ld x, 32
621 | copy one, many + x
573622 | }
574623 ? RangeExceededError
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