From c8c5795a48b87c7577acc351c21ee717f0e69d0a Mon Sep 17 00:00:00 2001
From: r4 <r4@nobrain.org>
Date: Tue, 16 Nov 2021 23:23:54 +0100
Subject: [PATCH] init

---
 Makefile |  15 ++++
 main.c   | 216 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 231 insertions(+)
 create mode 100644 Makefile
 create mode 100644 main.c

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..90db6fc
--- /dev/null
+++ b/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)
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..a37cebf
--- /dev/null
+++ b/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);
+}