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kconfig: add comments to expression transformations

Provide explanations for complex transformations.

Masahiro Yamada committed 2 years ago

Commit 4fa146e1 parent d607e0e1 file · +37 −6Browse files

Unified · Split

scripts/kconfig/expr.c+37−6
@@ -442,6 +442,7 @@ static struct expr *expr_join_or(struct expr *e1, struct expr *e2) · 441 unmodified lines
442442 }
443443 }
444444 if (sym1->type == S_BOOLEAN) {
445+ // a || !a -> y
445446 if ((e1->type == E_NOT && e1->left.expr->type == E_SYMBOL && e2->type == E_SYMBOL) ||
446447 (e2->type == E_NOT && e2->left.expr->type == E_SYMBOL && e1->type == E_SYMBOL))
447448 return expr_alloc_symbol(&symbol_yes);
@@ -647,6 +648,30 @@ struct expr *expr_eliminate_dups(struct expr *e) · 199 unmodified lines
647648 * Performs various simplifications involving logical operators and
648649 * comparisons.
649650 *
651+ * For bool type:
652+ * A=n -> !A
653+ * A=m -> n
654+ * A=y -> A
655+ * A!=n -> A
656+ * A!=m -> y
657+ * A!=y -> !A
658+ *
659+ * For any type:
660+ * !!A -> A
661+ * !(A=B) -> A!=B
662+ * !(A!=B) -> A=B
663+ * !(A<=B) -> A>B
664+ * !(A>=B) -> A<B
665+ * !(A<B) -> A>=B
666+ * !(A>B) -> A<=B
667+ * !(A || B) -> !A && !B
668+ * !(A && B) -> !A || !B
669+ *
670+ * For constant:
671+ * !y -> n
672+ * !m -> m
673+ * !n -> y
674+ *
650675 * Allocates and returns a new expression.
651676 */
652677 struct expr *expr_transform(struct expr *e)
@@ -674,12 +699,14 @@ struct expr *expr_transform(struct expr *e) · 21 unmodified lines
674699 if (e->left.sym->type != S_BOOLEAN)
675700 break;
676701 if (e->right.sym == &symbol_no) {
702+ // A=n -> !A
677703 e->type = E_NOT;
678704 e->left.expr = expr_alloc_symbol(e->left.sym);
679705 e->right.sym = NULL;
680706 break;
681707 }
682708 if (e->right.sym == &symbol_mod) {
709+ // A=m -> n
683710 printf("boolean symbol %s tested for 'm'? test forced to 'n'\n", e->left.sym->name);
684711 e->type = E_SYMBOL;
685712 e->left.sym = &symbol_no;
@@ -687,6 +714,7 @@ struct expr *expr_transform(struct expr *e) · 1 unmodified line
687714 break;
688715 }
689716 if (e->right.sym == &symbol_yes) {
717+ // A=y -> A
690718 e->type = E_SYMBOL;
691719 e->right.sym = NULL;
692720 break;
@@ -696,11 +724,13 @@ struct expr *expr_transform(struct expr *e) · 3 unmodified lines
696724 if (e->left.sym->type != S_BOOLEAN)
697725 break;
698726 if (e->right.sym == &symbol_no) {
727+ // A!=n -> A
699728 e->type = E_SYMBOL;
700729 e->right.sym = NULL;
701730 break;
702731 }
703732 if (e->right.sym == &symbol_mod) {
733+ // A!=m -> y
704734 printf("boolean symbol %s tested for 'm'? test forced to 'y'\n", e->left.sym->name);
705735 e->type = E_SYMBOL;
706736 e->left.sym = &symbol_yes;
@@ -708,6 +738,7 @@ struct expr *expr_transform(struct expr *e) · 1 unmodified line
708738 break;
709739 }
710740 if (e->right.sym == &symbol_yes) {
741+ // A!=y -> !A
711742 e->type = E_NOT;
712743 e->left.expr = expr_alloc_symbol(e->left.sym);
713744 e->right.sym = NULL;
@@ -717,7 +748,7 @@ struct expr *expr_transform(struct expr *e) · 3 unmodified lines
717748 case E_NOT:
718749 switch (e->left.expr->type) {
719750 case E_NOT:
720− // !!a -> a
751+ // !!A -> A
721752 tmp = e->left.expr->left.expr;
722753 free(e->left.expr);
723754 free(e);
@@ -726,7 +757,7 @@ struct expr *expr_transform(struct expr *e) · 2 unmodified lines
726757 break;
727758 case E_EQUAL:
728759 case E_UNEQUAL:
729− // !a='x' -> a!='x'
760+ // !(A=B) -> A!=B
730761 tmp = e->left.expr;
731762 free(e);
732763 e = tmp;
@@ -734,7 +765,7 @@ struct expr *expr_transform(struct expr *e) · 1 unmodified line
734765 break;
735766 case E_LEQ:
736767 case E_GEQ:
737− // !a<='x' -> a>'x'
768+ // !(A<=B) -> A>B
738769 tmp = e->left.expr;
739770 free(e);
740771 e = tmp;
@@ -742,14 +773,14 @@ struct expr *expr_transform(struct expr *e) · 1 unmodified line
742773 break;
743774 case E_LTH:
744775 case E_GTH:
745− // !a<'x' -> a>='x'
776+ // !(A<B) -> A>=B
746777 tmp = e->left.expr;
747778 free(e);
748779 e = tmp;
749780 e->type = e->type == E_LTH ? E_GEQ : E_LEQ;
750781 break;
751782 case E_OR:
752− // !(a || b) -> !a && !b
783+ // !(A || B) -> !A && !B
753784 tmp = e->left.expr;
754785 e->type = E_AND;
755786 e->right.expr = expr_alloc_one(E_NOT, tmp->right.expr);
@@ -758,7 +789,7 @@ struct expr *expr_transform(struct expr *e) · 2 unmodified lines
758789 e = expr_transform(e);
759790 break;
760791 case E_AND:
761− // !(a && b) -> !a || !b
792+ // !(A && B) -> !A || !B
762793 tmp = e->left.expr;
763794 e->type = E_OR;
764795 e->right.expr = expr_alloc_one(E_NOT, tmp->right.expr);