eqn.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

yystack:
	/* put a state and value onto the stack */
	if(yydebug >= 4)
		printf("char %s in %s", yytokname(yychar), yystatname(yystate));

	yyp++;
	if(yyp >= &yys[YYMAXDEPTH]) {
		yyerror("yacc stack overflow");
		goto ret1;
	}
	yyp->yys = yystate;
	yyp->yyv = yyval;

yynewstate:
	yyn = yypact[yystate];
	if(yyn <= YYFLAG)
		goto yydefault; /* simple state */
	if(yychar < 0)
		yychar = yylex1();
	yyn += yychar;
	if(yyn < 0 || yyn >= YYLAST)
		goto yydefault;
	yyn = yyact[yyn];
	if(yychk[yyn] == yychar) { /* valid shift */
		yychar = -1;
		yyval = yylval;
		yystate = yyn;
		if(yyerrflag > 0)
			yyerrflag--;
		goto yystack;
	}

yydefault:
	/* default state action */
	yyn = yydef[yystate];
	if(yyn == -2) {
		if(yychar < 0)
			yychar = yylex1();

		/* look through exception table */
		for(yyxi=yyexca;; yyxi+=2)
			if(yyxi[0] == -1 && yyxi[1] == yystate)
				break;
		for(yyxi += 2;; yyxi += 2) {
			yyn = yyxi[0];
			if(yyn < 0 || yyn == yychar)
				break;
		}
		yyn = yyxi[1];
		if(yyn < 0)
			goto ret0;
	}
	if(yyn == 0) {
		/* error ... attempt to resume parsing */
		switch(yyerrflag) {
		case 0:   /* brand new error */
			yyerror("syntax error");
			if(yydebug >= 1) {
				printf("%s", yystatname(yystate));
				printf("saw %s\n", yytokname(yychar));
			}
yyerrlab:
			yynerrs++;

		case 1:
		case 2: /* incompletely recovered error ... try again */
			yyerrflag = 3;

			/* find a state where "error" is a legal shift action */
			while(yyp >= yys) {
				yyn = yypact[yyp->yys] + YYERRCODE;
				if(yyn >= 0 && yyn < YYLAST) {
					yystate = yyact[yyn];  /* simulate a shift of "error" */
					if(yychk[yystate] == YYERRCODE)
						goto yystack;
				}

				/* the current yyp has no shift onn "error", pop stack */
				if(yydebug >= 2)
					printf("error recovery pops state %d, uncovers %d\n",
						yyp->yys, (yyp-1)->yys );
				yyp--;
			}
			/* there is no state on the stack with an error shift ... abort */
			goto ret1;

		case 3:  /* no shift yet; clobber input char */
			if(yydebug >= YYEOFCODE)
				printf("error recovery discards %s\n", yytokname(yychar));
			if(yychar == YYEOFCODE)
				goto ret1;
			yychar = -1;
			goto yynewstate;   /* try again in the same state */
		}
	}

	/* reduction by production yyn */
	if(yydebug >= 2)
		printf("reduce %d in:\n\t%s", yyn, yystatname(yystate));

	yypt = yyp;
	yyp -= yyr2[yyn];
	yyval = (yyp+1)->yyv;
	yym = yyn;

	/* consult goto table to find next state */
	yyn = yyr1[yyn];
	yyg = yypgo[yyn];
	yyj = yyg + yyp->yys + 1;

	if(yyj >= YYLAST || yychk[yystate=yyact[yyj]] != -yyn)
		yystate = yyact[yyg];
	switch(yym) {
		
case 1:
#line	24	"/sys/src/cmd/eqn/eqn.y"
{ putout(yypt[-0].yyv); } break;
case 2:
#line	25	"/sys/src/cmd/eqn/eqn.y"
{ ERROR "syntax error" WARNING; } break;
case 3:
#line	26	"/sys/src/cmd/eqn/eqn.y"
{ eqnreg = 0; } break;
case 5:
#line	30	"/sys/src/cmd/eqn/eqn.y"
{ eqnbox(yypt[-1].yyv, yypt[-0].yyv, 0); } break;
case 6:
#line	31	"/sys/src/cmd/eqn/eqn.y"
{ eqnbox(yypt[-1].yyv, yypt[-0].yyv, 1); } break;
case 7:
#line	32	"/sys/src/cmd/eqn/eqn.y"
{ lineup(0); } break;
case 8:
#line	35	"/sys/src/cmd/eqn/eqn.y"
{ yyval = yypt[-0].yyv; lineup(1); } break;
case 9:
#line	38	"/sys/src/cmd/eqn/eqn.y"
{ yyval = yypt[-0].yyv; } break;
case 10:
#line	39	"/sys/src/cmd/eqn/eqn.y"
{ yyval = 0; } break;
case 11:
#line	42	"/sys/src/cmd/eqn/eqn.y"
{ yyval = yypt[-0].yyv; } break;
case 12:
#line	43	"/sys/src/cmd/eqn/eqn.y"
{ yyval = 0; } break;
case 13:
#line	46	"/sys/src/cmd/eqn/eqn.y"
{ yyval = yypt[-1].yyv; } break;
case 14:
#line	47	"/sys/src/cmd/eqn/eqn.y"
{ text(QTEXT, (char *) yypt[-0].yyv); } break;
case 15:
#line	48	"/sys/src/cmd/eqn/eqn.y"
{ text(CONTIG, (char *) yypt[-0].yyv); } break;
case 16:
#line	49	"/sys/src/cmd/eqn/eqn.y"
{ text(SPACE, (char *) 0); } break;
case 17:
#line	50	"/sys/src/cmd/eqn/eqn.y"
{ text(THIN, (char *) 0); } break;
case 18:
#line	51	"/sys/src/cmd/eqn/eqn.y"
{ text(TAB, (char *) 0); } break;
case 19:
#line	52	"/sys/src/cmd/eqn/eqn.y"
{ funny(SUM); } break;
case 20:
#line	53	"/sys/src/cmd/eqn/eqn.y"
{ funny(PROD); } break;
case 21:
#line	54	"/sys/src/cmd/eqn/eqn.y"
{ funny(UNION); } break;
case 22:
#line	55	"/sys/src/cmd/eqn/eqn.y"
{ funny(INTER); } break;
case 23:
#line	56	"/sys/src/cmd/eqn/eqn.y"
{ boverb(yypt[-2].yyv, yypt[-0].yyv); } break;
case 24:
#line	57	"/sys/src/cmd/eqn/eqn.y"
{ mark(yypt[-0].yyv); } break;
case 25:
#line	58	"/sys/src/cmd/eqn/eqn.y"
{ size(yypt[-1].yyv, yypt[-0].yyv); } break;
case 26:
#line	59	"/sys/src/cmd/eqn/eqn.y"
{ font(yypt[-1].yyv, yypt[-0].yyv); } break;
case 27:
#line	60	"/sys/src/cmd/eqn/eqn.y"
{ fatbox(yypt[-0].yyv); } break;
case 28:
#line	61	"/sys/src/cmd/eqn/eqn.y"
{ sqrt(yypt[-0].yyv); } break;
case 29:
#line	62	"/sys/src/cmd/eqn/eqn.y"
{ps -= deltaps;} break;
case 30:
#line	62	"/sys/src/cmd/eqn/eqn.y"
{ subsup(yypt[-4].yyv, yypt[-1].yyv, yypt[-0].yyv); } break;
case 31:
#line	63	"/sys/src/cmd/eqn/eqn.y"
{ps -= deltaps;} break;
case 32:
#line	63	"/sys/src/cmd/eqn/eqn.y"
{ subsup(yypt[-3].yyv, 0, yypt[-0].yyv); } break;
case 33:
#line	64	"/sys/src/cmd/eqn/eqn.y"
{ps -= deltaps;} break;
case 34:
#line	64	"/sys/src/cmd/eqn/eqn.y"
{ integral(yypt[-4].yyv, yypt[-1].yyv, yypt[-0].yyv); } break;
case 35:
#line	65	"/sys/src/cmd/eqn/eqn.y"
{ps -= deltaps;} break;
case 36:
#line	65	"/sys/src/cmd/eqn/eqn.y"
{ integral(yypt[-3].yyv, 0, yypt[-0].yyv); } break;
case 37:
#line	66	"/sys/src/cmd/eqn/eqn.y"
{ integral(yypt[-0].yyv, 0, 0); } break;
case 38:
#line	67	"/sys/src/cmd/eqn/eqn.y"
{ps -= deltaps;} break;
case 39:
#line	67	"/sys/src/cmd/eqn/eqn.y"
{ fromto(yypt[-4].yyv, yypt[-1].yyv, yypt[-0].yyv); } break;
case 40:
#line	68	"/sys/src/cmd/eqn/eqn.y"
{ps -= deltaps;} break;
case 41:
#line	68	"/sys/src/cmd/eqn/eqn.y"
{ fromto(yypt[-3].yyv, 0, yypt[-0].yyv); } break;
case 42:
#line	69	"/sys/src/cmd/eqn/eqn.y"
{ paren(yypt[-2].yyv, yypt[-1].yyv, yypt[-0].yyv); } break;
case 43:
#line	70	"/sys/src/cmd/eqn/eqn.y"
{ paren(yypt[-1].yyv, yypt[-0].yyv, 0); } break;
case 44:
#line	71	"/sys/src/cmd/eqn/eqn.y"
{ diacrit(yypt[-1].yyv, yypt[-0].yyv); } break;
case 45:
#line	72	"/sys/src/cmd/eqn/eqn.y"
{ move(FWD, yypt[-1].yyv, yypt[-0].yyv); } break;
case 46:
#line	73	"/sys/src/cmd/eqn/eqn.y"
{ move(UP, yypt[-1].yyv, yypt[-0].yyv); } break;
case 47:
#line	74	"/sys/src/cmd/eqn/eqn.y"
{ move(BACK, yypt[-1].yyv, yypt[-0].yyv); } break;
case 48:
#line	75	"/sys/src/cmd/eqn/eqn.y"
{ move(DOWN, yypt[-1].yyv, yypt[-0].yyv); } break;
case 49:
#line	76	"/sys/src/cmd/eqn/eqn.y"
{ pile(yypt[-0].yyv); ct = yypt[-0].yyv; } break;
case 50:
#line	77	"/sys/src/cmd/eqn/eqn.y"
{yyval=ct;} break;
case 51:
#line	77	"/sys/src/cmd/eqn/eqn.y"
{ matrix(yypt[-3].yyv); ct = yypt[-3].yyv; } break;
case 52:
#line	80	"/sys/src/cmd/eqn/eqn.y"
{ setintegral(); } break;
case 53:
#line	83	"/sys/src/cmd/eqn/eqn.y"
{ yyval = atoi((char *) yypt[-1].yyv); } break;
case 54:
#line	84	"/sys/src/cmd/eqn/eqn.y"
{ yyval = atoi((char *) yypt[-1].yyv); } break;
case 55:
#line	85	"/sys/src/cmd/eqn/eqn.y"
{ yyval = atoi((char *) yypt[-1].yyv); } break;
case 56:
#line	86	"/sys/src/cmd/eqn/eqn.y"
{ yyval = atoi((char *) yypt[-1].yyv); } break;
case 57:
#line	88	"/sys/src/cmd/eqn/eqn.y"
{ yyval = HAT; } break;
case 58:
#line	89	"/sys/src/cmd/eqn/eqn.y"
{ yyval = VEC; } break;
case 59:
#line	90	"/sys/src/cmd/eqn/eqn.y"
{ yyval = DYAD; } break;
case 60:
#line	91	"/sys/src/cmd/eqn/eqn.y"
{ yyval = BAR; } break;
case 61:
#line	92	"/sys/src/cmd/eqn/eqn.y"
{ yyval = LOWBAR; } break;
case 62:
#line	93	"/sys/src/cmd/eqn/eqn.y"
{ yyval = HIGHBAR; } break;
case 63:
#line	94	"/sys/src/cmd/eqn/eqn.y"
{ yyval = UNDER; } break;
case 64:
#line	95	"/sys/src/cmd/eqn/eqn.y"
{ yyval = DOT; } break;
case 65:
#line	96	"/sys/src/cmd/eqn/eqn.y"
{ yyval = TILDE; } break;
case 66:
#line	97	"/sys/src/cmd/eqn/eqn.y"
{ yyval = UTILDE; } break;
case 67:
#line	98	"/sys/src/cmd/eqn/eqn.y"
{ yyval = DOTDOT; } break;
case 68:
#line	101	"/sys/src/cmd/eqn/eqn.y"
{ yyval = ((char *)yypt[-0].yyv)[0]; } break;
case 69:
#line	102	"/sys/src/cmd/eqn/eqn.y"
{ yyval = '{'; } break;
case 70:
#line	105	"/sys/src/cmd/eqn/eqn.y"
{ yyval = ((char *)yypt[-0].yyv)[0]; } break;
case 71:
#line	106	"/sys/src/cmd/eqn/eqn.y"
{ yyval = '}'; } break;
case 74:
#line	113	"/sys/src/cmd/eqn/eqn.y"
{ column(yypt[-3].yyv, DEFGAP); } break;
case 75:
#line	114	"/sys/src/cmd/eqn/eqn.y"
{yyval=atoi((char*)yypt[-0].yyv);} break;
case 76:
#line	114	"/sys/src/cmd/eqn/eqn.y"
{ column(yypt[-5].yyv, yypt[-3].yyv); } break;
case 77:
#line	117	"/sys/src/cmd/eqn/eqn.y"
{ yyval = startcol(LCOL); } break;
case 78:
#line	118	"/sys/src/cmd/eqn/eqn.y"
{ yyval = startcol(CCOL); } break;
case 79:
#line	119	"/sys/src/cmd/eqn/eqn.y"
{ yyval = startcol(RCOL); } break;
case 80:
#line	120	"/sys/src/cmd/eqn/eqn.y"
{ yyval = startcol(COL); } break;
case 81:
#line	123	"/sys/src/cmd/eqn/eqn.y"
{ lp[ct++] = yypt[-0].yyv; } break;
case 82:
#line	124	"/sys/src/cmd/eqn/eqn.y"
{ lp[ct++] = yypt[-0].yyv; } break;
case 83:
#line	127	"/sys/src/cmd/eqn/eqn.y"
{ yyval = ps; setsize((char *) yypt[-0].yyv); } break;
case 84:
#line	130	"/sys/src/cmd/eqn/eqn.y"
{ static char R[]="R"; setfont(R); } break;
case 85:
#line	131	"/sys/src/cmd/eqn/eqn.y"
{ static char I[]="I"; setfont(I); } break;
case 86:
#line	132	"/sys/src/cmd/eqn/eqn.y"
{ static char B[]="B"; setfont(B); } break;
case 87:
#line	133	"/sys/src/cmd/eqn/eqn.y"
{ setfont((char *)yypt[-0].yyv); } break;
	}
	goto yystack;  /* stack new state and value */
}