From 9f298a2098fa244ac763bc4d22ccf3fb7c9760bb Mon Sep 17 00:00:00 2001
From: Thomas Voss <mail@thomasvoss.com>
Date: Wed, 4 Oct 2023 21:41:42 +0200
Subject: Genesis commit

---
 main.l | 171 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 171 insertions(+)
 create mode 100644 main.l

(limited to 'main.l')

diff --git a/main.l b/main.l
new file mode 100644
index 0000000..9478c16
--- /dev/null
+++ b/main.l
@@ -0,0 +1,171 @@
+%{
+#include <err.h>
+#include <getopt.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define YY_USER_ACTION ECHO;
+
+const char empty_field[] = "argument to the -p option contains an empty field";
+const char invalid_char[] = "argument to the -p option must be a "
+                            "comma-seperated list of positive integers";
+const char final_comma[] = "argument to the -p option contains trailing comma";
+
+const char *argv0;
+unsigned pos;
+struct {
+	unsigned *ps;
+	size_t len;
+} positions;
+
+static void usage(void);
+static void append_positions(char *s);
+static int ucmp(const void *, const void *);
+static unsigned atou(const char *);
+static bool print_ordinal(void);
+%}
+
+%option nodefault noinput nounput
+
+%%
+
+[0-9]*(1[0-9]|[04-9]) { pos++; if (print_ordinal()) fputs("th", stdout); }
+[0-9]*1               { pos++; if (print_ordinal()) fputs("st", stdout); }
+[0-9]*2               { pos++; if (print_ordinal()) fputs("nd", stdout); }
+[0-9]*3               { pos++; if (print_ordinal()) fputs("rd", stdout); }
+
+\n { pos = 0; }
+[^0-9\n]+ ;
+
+%%
+
+void
+usage(void)
+{
+	fprintf(stderr, "Usage: %s [-p indicies ...] [file ...]\n", argv0);
+	exit(EXIT_FAILURE);
+}
+
+int
+main(int argc, char **argv)
+{
+	int opt, rv;
+	struct option longopts[] = {
+		{"positions", required_argument, 0, 'p'},
+		{ NULL,       0,                 0,  0 }
+	};
+
+	argv0 = argv[0];
+	rv = EXIT_SUCCESS;
+
+	while ((opt = getopt_long(argc, argv, "p:", longopts, NULL)) != -1) {
+		switch (opt) {
+		case 'p':
+			append_positions(optarg);
+			break;
+		default:
+			usage();
+		}
+	}
+
+	argc -= optind;
+	argv += optind;
+
+	if (argc == 0)
+		yylex();
+	for (int i = 0; i < argc; i++) {
+		if (strcmp(argv[i], "-") == 0)
+			yyin = stdin;
+		else if ((yyin = fopen(argv[i], "r")) == NULL) {
+			warn("fopen: %s", argv[i]);
+			rv = EXIT_FAILURE;
+			continue;
+		}
+		yylex();
+		if (yyin != stdin)
+			fclose(yyin);
+	}
+
+	return rv;
+}
+
+void
+append_positions(char *raw)
+{
+	bool comma = true;
+	const char *s;
+
+	if (positions.ps != NULL) {
+		warnx("the -p option should only be provided once");
+		usage();
+	}
+
+	for (s = raw, positions.len++; *s; s++) {
+		switch (*s) {
+		case ',':
+			if (comma)
+				errx(EXIT_FAILURE, empty_field);
+			comma = true;
+			positions.len++;
+			break;
+		case '0': case '1': case '2': case '3': case '4':
+		case '5': case '6': case '7': case '8': case '9':
+			comma = false;
+			break;
+		default:
+			errx(EXIT_FAILURE, invalid_char);
+		}
+	}
+
+	if (comma == true)
+		errx(EXIT_FAILURE, final_comma);
+
+	if ((positions.ps = malloc(sizeof(unsigned *) * positions.len)) == NULL)
+		err(EXIT_FAILURE, "malloc");
+
+	/* Iterate over each position, parse it, and sort the results.  It’s
+	   safe to use strtok() and atou() here since the input string has been
+	   pre-validated. */
+	s = strtok(raw, ",");
+	for (size_t i = 0; s != NULL; i++) {
+		positions.ps[i] = atou(s);
+		s = strtok(NULL, ",");
+	}
+	qsort(positions.ps, positions.len, sizeof(unsigned), ucmp);
+}
+
+int
+ucmp(const void *a, const void *b)
+{
+	unsigned a_ = *(unsigned *)a,
+	         b_ = *(unsigned *)b;
+	return a_ > b_ ? 1 : b_ < a_ ? -1 : 0;
+}
+
+unsigned
+atou(const char *s)
+{
+	unsigned n = 0;
+	for (; *s; s++)
+		n = n * 10 + *s - '0';
+	return n;
+}
+
+bool
+print_ordinal(void)
+{
+	/* Basic binary search */
+	for (size_t l = 0, r = positions.len - 1, m; l <= r;) {
+		m = l + (r - l) / 2;
+		if (positions.ps[m] == pos)
+			return true;
+		if (positions.ps[m] > pos)
+			r = m - 1;
+		else
+			l = m + 1;
+	}
+
+	return false;
+}
-- 
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