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/* file: "tinyc.c" */
/* Copyright (C) 2001 by Marc Feeley, All Rights Reserved. */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/*
* This is a compiler for the Tiny-C language. Tiny-C is a
* considerably stripped down version of C and it is meant as a
* pedagogical tool for learning about compilers. The integer global
* variables "a" to "z" are predefined and initialized to zero, and it
* is not possible to declare new variables. The compiler reads the
* program from standard input and prints out the value of the
* variables that are not zero. The grammar of Tiny-C in EBNF is:
*
* <program> ::= <statement>
* <statement> ::= "if" <paren_expr> <statement> |
* "if" <paren_expr> <statement> "else" <statement> |
* "while" <paren_expr> <statement> |
* "do" <statement> "while" <paren_expr> ";" |
* "{" { <statement> } "}" |
* <expr> ";" |
* ";"
* <paren_expr> ::= "(" <expr> ")"
* <expr> ::= <test> | <id> "=" <expr>
* <test> ::= <sum> | <sum> "<" <sum>
* <sum> ::= <term> | <sum> "+" <term> | <sum> "-" <term>
* <term> ::= <id> | <int> | <paren_expr>
* <id> ::= "a" | "b" | "c" | "d" | ... | "z"
* <int> ::= <an_unsigned_decimal_integer>
*
* Here are a few invocations of the compiler:
*
* % echo "a=b=c=2<3;" | ./a.out
* a = 1
* b = 1
* c = 1
* % echo "{ i=1; while (i<100) i=i+i; }" | ./a.out
* i = 128
* % echo "{ i=125; j=100; while (i-j) if (i<j) j=j-i; else i=i-j; }" | ./a.out
* i = 25
* j = 25
* % echo "{ i=1; do i=i+10; while (i<50); }" | ./a.out
* i = 51
* % echo "{ i=1; while ((i=i+10)<50) ; }" | ./a.out
* i = 51
* % echo "{ i=7; if (i<5) x=1; if (i<10) y=2; }" | ./a.out
* i = 7
* y = 2
*
* The compiler does a minimal amount of error checking to help
* highlight the structure of the compiler.
*/
/*---------------------------------------------------------------------------*/
/* Lexer. */
enum { DO_SYM, ELSE_SYM, IF_SYM, WHILE_SYM, LBRA, RBRA, LPAR, RPAR,
PLUS, MINUS, LESS, SEMI, EQUAL, INT, ID, EOI };
char *words[] = { "do", "else", "if", "while", NULL };
int ch = ' ';
int sym;
int int_val;
char id_name[100];
void syntax_error() { fprintf(stderr, "syntax error\n"); exit(1); }
void next_ch() { ch = getchar(); }
void next_sym()
{ again: switch (ch)
{ case ' ': case '\n': next_ch(); goto again;
case EOF: sym = EOI; break;
case '{': next_ch(); sym = LBRA; break;
case '}': next_ch(); sym = RBRA; break;
case '(': next_ch(); sym = LPAR; break;
case ')': next_ch(); sym = RPAR; break;
case '+': next_ch(); sym = PLUS; break;
case '-': next_ch(); sym = MINUS; break;
case '<': next_ch(); sym = LESS; break;
case ';': next_ch(); sym = SEMI; break;
case '=': next_ch(); sym = EQUAL; break;
default:
if (ch >= '0' && ch <= '9')
{ int_val = 0; /* missing overflow check */
while (ch >= '0' && ch <= '9')
{ int_val = int_val*10 + (ch - '0'); next_ch(); }
sym = INT;
}
else if (ch >= 'a' && ch <= 'z')
{ int i = 0; /* missing overflow check */
while ((ch >= 'a' && ch <= 'z') || ch == '_')
{ id_name[i++] = ch; next_ch(); }
id_name[i] = '\0';
sym = 0;
while (words[sym] != NULL && strcmp(words[sym], id_name) != 0)
sym++;
if (words[sym] == NULL)
if (id_name[1] == '\0') sym = ID; else syntax_error();
}
else
syntax_error();
}
}
/*---------------------------------------------------------------------------*/
/* Parser. */
enum { VAR, CST, ADD, SUB, LT, SET,
IF1, IF2, WHILE, DO, EMPTY, SEQ, EXPR, PROG };
struct node { int kind; struct node *o1, *o2, *o3; int val; };
typedef struct node node;
node *new_node(int k)
{ node *x = (node*)malloc(sizeof(node)); x->kind = k; return x; }
node *paren_expr(); /* forward declaration */
node *term() /* <term> ::= <id> | <int> | <paren_expr> */
{ node *x;
if (sym == ID) { x=new_node(VAR); x->val=id_name[0]-'a'; next_sym(); }
else if (sym == INT) { x=new_node(CST); x->val=int_val; next_sym(); }
else x = paren_expr();
return x;
}
node *sum() /* <sum> ::= <term> | <sum> "+" <term> | <sum> "-" <term> */
{ node *t, *x = term();
while (sym == PLUS || sym == MINUS)
{ t=x; x=new_node(sym==PLUS?ADD:SUB); next_sym(); x->o1=t; x->o2=term(); }
return x;
}
node *test() /* <test> ::= <sum> | <sum> "<" <sum> */
{ node *t, *x = sum();
if (sym == LESS)
{ t=x; x=new_node(LT); next_sym(); x->o1=t; x->o2=sum(); }
return x;
}
node *expr() /* <expr> ::= <test> | <id> "=" <expr> */
{ node *t, *x;
if (sym != ID) return test();
x = test();
if (x->kind == VAR && sym == EQUAL)
{ t=x; x=new_node(SET); next_sym(); x->o1=t; x->o2=expr(); }
return x;
}
node *paren_expr() /* <paren_expr> ::= "(" <expr> ")" */
{ node *x;
if (sym == LPAR) next_sym(); else syntax_error();
x = expr();
if (sym == RPAR) next_sym(); else syntax_error();
return x;
}
node *statement()
{ node *t, *x;
if (sym == IF_SYM) /* "if" <paren_expr> <statement> */
{ x = new_node(IF1);
next_sym();
x->o1 = paren_expr();
x->o2 = statement();
if (sym == ELSE_SYM) /* ... "else" <statement> */
{ x->kind = IF2;
next_sym();
x->o3 = statement();
}
}
else if (sym == WHILE_SYM) /* "while" <paren_expr> <statement> */
{ x = new_node(WHILE);
next_sym();
x->o1 = paren_expr();
x->o2 = statement();
}
else if (sym == DO_SYM) /* "do" <statement> "while" <paren_expr> ";" */
{ x = new_node(DO);
next_sym();
x->o1 = statement();
if (sym == WHILE_SYM) next_sym(); else syntax_error();
x->o2 = paren_expr();
if (sym == SEMI) next_sym(); else syntax_error();
}
else if (sym == SEMI) /* ";" */
{ x = new_node(EMPTY); next_sym(); }
else if (sym == LBRA) /* "{" { <statement> } "}" */
{ x = new_node(EMPTY);
next_sym();
while (sym != RBRA)
{ t=x; x=new_node(SEQ); x->o1=t; x->o2=statement(); }
next_sym();
}
else /* <expr> ";" */
{ x = new_node(EXPR);
x->o1 = expr();
if (sym == SEMI) next_sym(); else syntax_error();
}
return x;
}
node *program() /* <program> ::= <statement> */
{ node *x = new_node(PROG);
next_sym(); x->o1 = statement(); if (sym != EOI) syntax_error();
return x;
}
/*---------------------------------------------------------------------------*/
/* Code generator. */
enum { IFETCH, ISTORE, IPUSH, IPOP, IADD, ISUB, ILT, JZ, JNZ, JMP, HALT };
typedef char code;
code object[1000], *here = object;
void g(code c) { *here++ = c; } /* missing overflow check */
code *hole() { return here++; }
void fix(code *src, code *dst) { *src = dst-src; } /* missing overflow check */
void c(node *x)
{ code *p1, *p2;
switch (x->kind)
{ case VAR : g(IFETCH); g(x->val); break;
case CST : g(IPUSH); g(x->val); break;
case ADD : c(x->o1); c(x->o2); g(IADD); break;
case SUB : c(x->o1); c(x->o2); g(ISUB); break;
case LT : c(x->o1); c(x->o2); g(ILT); break;
case SET : c(x->o2); g(ISTORE); g(x->o1->val); break;
case IF1 : c(x->o1); g(JZ); p1=hole(); c(x->o2); fix(p1,here); break;
case IF2 : c(x->o1); g(JZ); p1=hole(); c(x->o2); g(JMP); p2=hole();
fix(p1,here); c(x->o3); fix(p2,here); break;
case WHILE: p1=here; c(x->o1); g(JZ); p2=hole(); c(x->o2);
g(JMP); fix(hole(),p1); fix(p2,here); break;
case DO : p1=here; c(x->o1); c(x->o2); g(JNZ); fix(hole(),p1); break;
case EMPTY: break;
case SEQ : c(x->o1); c(x->o2); break;
case EXPR : c(x->o1); g(IPOP); break;
case PROG : c(x->o1); g(HALT); break;
}
}
/*---------------------------------------------------------------------------*/
/* Virtual machine. */
int globals[26];
void run()
{ int stack[1000], *sp = stack;
code *pc = object;
again: switch (*pc++)
{ case IFETCH: *sp++ = globals[*pc++]; goto again;
case ISTORE: globals[*pc++] = sp[-1]; goto again;
case IPUSH : *sp++ = *pc++; goto again;
case IPOP : --sp; goto again;
case IADD : sp[-2] = sp[-2] + sp[-1]; --sp; goto again;
case ISUB : sp[-2] = sp[-2] - sp[-1]; --sp; goto again;
case ILT : sp[-2] = sp[-2] < sp[-1]; --sp; goto again;
case JMP : pc += *pc; goto again;
case JZ : if (*--sp == 0) pc += *pc; else pc++; goto again;
case JNZ : if (*--sp != 0) pc += *pc; else pc++; goto again;
}
}
/*---------------------------------------------------------------------------*/
/* Main program. */
int main()
{ int i;
c(program());
for (i=0; i<26; i++)
globals[i] = 0;
run();
for (i=0; i<26; i++)
if (globals[i] != 0)
printf("%c = %d\n", 'a'+i, globals[i]);
return 0;
}
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