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r4 2 months ago
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  1. 15
      Makefile
  2. 216
      main.c

15
Makefile

@ -0,0 +1,15 @@
LDFLAGS =
#CFLAGS = -Ofast -march=native -Wall -pedantic -Werror -lm
CFLAGS = -ggdb -march=native -Wall -pedantic -Werror -lm
CC = cc
EXE = exp
all: $(EXE)
$(EXE): main.c
$(CC) -o $@ $^ $(LDFLAGS) $(CFLAGS)
.PHONY: clean
clean:
rm -f $(EXE)

216
main.c

@ -0,0 +1,216 @@
#include <math.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef double real;
typedef struct Tok {
enum {
TokOp,
TokNum,
} kind;
union {
real Num;
char Char;
};
} Tok;
#define TOKS_CAP 65536
Tok toks[TOKS_CAP];
size_t toks_size = 0;
uint8_t op_prec[256] = {
['('] = 0,
[')'] = 0,
['+'] = 1,
['-'] = 1,
['*'] = 2,
['/'] = 2,
['^'] = 3,
};
enum {
OrderLtr,
OrderRtl,
} op_order[256] = {
['('] = OrderLtr,
[')'] = OrderLtr,
['+'] = OrderLtr,
['-'] = OrderLtr,
['*'] = OrderLtr,
['/'] = OrderLtr,
['^'] = OrderRtl,
};
#define IS_FLOAT(c) ((c >= '0' && c <= '9') || c == '.')
void push_tok(Tok t) {
if (toks_size+1 < TOKS_CAP)
toks[toks_size++] = t;
}
void tokenize(char *expr) {
push_tok((Tok){.kind = TokOp, .Char = '('});
size_t paren_depth = 0;
bool can_be_neg_num = true;
char *curr = expr;
for (char c = *curr; c != 0; c = *(++curr)) {
if (c == ' ')
continue;
if (IS_FLOAT(c) ||
(can_be_neg_num && c == '-' && IS_FLOAT(curr[1]))) {
char buf[16];
size_t i = 0;
while (IS_FLOAT(curr[i]) && i < 15) {
buf[i] = curr[i];
i++;
}
curr += i - 1;
buf[i++] = 0;
real num = strtod(buf, NULL);
push_tok((Tok){.kind = TokNum, .Num = num});
can_be_neg_num = false;
continue;
}
if (c == '(')
paren_depth++;
else if (c == ')') {
if (paren_depth == 0) {
fprintf(stderr, "Error: unmatched ')'\n");
exit(1);
}
paren_depth--;
}
switch (c) {
case '(':
case ')':
case '+':
case '-':
case '*':
case '/':
case '^': {
push_tok((Tok){.kind = TokOp, .Char = c});
break;
}
default:
fprintf(stderr, "Error: unrecognized token at %zd: '%c'\n", curr - expr, c);
exit(1);
}
can_be_neg_num = c != ')';
}
if (paren_depth > 0) {
fprintf(stderr, "Error: unmatched '('\n");
exit(1);
}
push_tok((Tok){.kind = TokOp, .Char = ')'});
}
void print_toks() {
for (size_t i = 0; i < toks_size; i++) {
switch (toks[i].kind) {
case TokOp:
if (toks[i].Char == 0) {
fprintf(stderr, "Error: unexpected end of token stream\n");
exit(1);
}
printf("%c ", toks[i].Char);
break;
case TokNum:
printf("%.2f ", toks[i].Num);
break;
default:
fprintf(stderr, "Error: unhandled token\n");
exit(1);
}
}
printf("\n");
}
void del_toks(Tok *begin, Tok *end) {
memmove(begin, end, (toks_size - (end - toks)) * sizeof(Tok));
toks_size -= end - begin;
}
real eval(Tok *t) {
if (!(t[0].kind == TokOp && t[0].Char == '(')) {
fprintf(stderr, "Error: expected '(' at beginning of expression\n");
exit(1);
}
while (1) {
/* Collapse parentheses. */
if (t[1].kind == TokOp && t[1].Char == '(') {
real res = eval(t + 1);
size_t i;
for (i = 2; !(t[i].kind == TokOp && t[i].Char == ')'); i++);
del_toks(t + 1, t + i);
/* Put the newly evaluated value into place. */
t[1].kind = TokNum;
t[1].Num = res;
}
if (!(t[0].kind == TokOp && t[1].kind == TokNum && t[2].kind == TokOp)) {
fprintf(stderr, "Error: invalid token order\n");
exit(1);
}
const char curr_op = t[0].Char;
const uint8_t curr_prec = op_prec[(size_t)curr_op];
const char next_op = t[2].Char;
const uint8_t next_prec = op_prec[(size_t)next_op];
if (curr_op == '(' && next_op == ')')
return t[1].Num;
if (next_prec > curr_prec || (next_prec == curr_prec && op_order[(size_t)curr_op] == OrderRtl)) {
t += 2;
} else if (next_prec < curr_prec || (next_prec == curr_prec && op_order[(size_t)curr_op] == OrderLtr)) {
real res;
real lhs = t[-1].Num, rhs = t[1].Num;
switch (curr_op) {
case '+': res = lhs + rhs; break;
case '-': res = lhs - rhs; break;
case '*': res = lhs * rhs; break;
case '/': res = lhs / rhs; break;
case '^': res = pow(lhs, rhs); break;
default:
fprintf(stderr, "Error: unhandled operator '%c'\n", t[1].Char);
exit(1);
}
t[1].Num = res;
del_toks(t - 1, t + 1);
t -= 2;
}
}
}
int main(int argc, char **argv) {
if (argc != 2 || strcmp(argv[1], "-h") == 0 || strcmp(argv[1], "--help") == 0) {
fprintf(stderr, "Usage: ./exp \"<expression>\"\n");
exit(1);
}
tokenize(argv[1]);
print_toks();
real res = eval(toks);
printf("Result: %f\n", res);
}
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