From 0140712af344cb984390981bbed4e864eb12027b Mon Sep 17 00:00:00 2001
From: Peter <peterr.00000@gmail.com>
Date: Mon, 14 Aug 2023 12:49:00 +0000
Subject: [PATCH] lab3 solutions `make_pathname`

---
 .gitignore            |  9 +++++
 lab03/make_pathname.c | 88 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 97 insertions(+)
 create mode 100644 lab03/make_pathname.c

diff --git a/.gitignore b/.gitignore
index e69de29..9a1cd8a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -0,0 +1,9 @@
+*
+!/**/
+!*.*
+
+*.o
+
+a.out
+
+test*/
\ No newline at end of file
diff --git a/lab03/make_pathname.c b/lab03/make_pathname.c
new file mode 100644
index 0000000..57b3479
--- /dev/null
+++ b/lab03/make_pathname.c
@@ -0,0 +1,88 @@
+// gcc make_pathname.c  -pedantic -Wall -Wextra -Wconversion -fsanitize=undefined,address -g -O0
+
+// You can assume the following headers have already been included: stdio.h,
+// stdlib.h, limits.h, ctype.h, stdbool.h, stdint.h, and string.h.
+#include <stdio.h>
+#include <stdlib.h>
+#include <limits.h>
+#include <ctype.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+
+#define SLASH_LEN 1
+#define DOT_LEN 1
+#define NULL_LEN 1
+#define SUM_LEN (SLASH_LEN + DOT_LEN + NULL_LEN)
+
+void fill_buffer(
+    const char *dir, size_t dirlen, const char *fname, size_t filelen,
+    const char *ext, size_t extlen, char *path)
+{
+    memcpy(path, dir, dirlen);
+    path[dirlen] = '/';
+    memcpy(path + dirlen + SLASH_LEN, fname, filelen);
+    path[dirlen + SLASH_LEN + filelen] = '.';
+    memcpy(path + dirlen + SLASH_LEN + filelen + DOT_LEN, ext, extlen);
+    path[dirlen + SLASH_LEN + filelen + DOT_LEN + extlen] = '\0';
+}
+
+/** Return true when the sum of dirlen, filelen, extlen and 3
+ * would exceed the maximum possible value of a size_t; otherwise,
+ * return false.
+ */
+bool would_wrap_around(size_t dirlen, size_t filelen, size_t extlen)
+{
+    return (SUM_LEN + dirlen + filelen < filelen             //
+            || SUM_LEN + dirlen + filelen < dirlen           //
+            || SUM_LEN + filelen + extlen < extlen           //
+            || SUM_LEN + filelen + extlen < filelen          //
+            || SUM_LEN + dirlen + extlen < dirlen            //
+            || SUM_LEN + dirlen + extlen < extlen            //
+            || SUM_LEN + dirlen + extlen + filelen < dirlen  //
+            || SUM_LEN + dirlen + extlen + filelen < filelen //
+            || SUM_LEN + dirlen + extlen + filelen < extlen  //
+    );
+}
+
+// Concatenates dir, fname and ext, with a forward slash ('/') between dir and
+// fname and a full stop ('.') between fname and ext.
+//
+// The return value is normally a pointer to dynamically allocated memory
+// containing this concatenated string, which should be freed by the caller
+// after use.
+//
+// If, however, the system cannot allocate sufficient memory to hold the
+// resulting string, then a NULL pointer is returned.
+//
+// Each of dir, fname and ext must be valid null-terminated strings;
+// furthermore, the fname and ext parameters must not contain any forward-slash
+// or full stop characters. If any of these conditions do not hold, the result
+// of calling the function is undefined.
+char *make_pathname(const char *dir, const char *fname, const char *ext)
+{
+    size_t dirlen = strlen(dir);
+    size_t filelen = strlen(fname);
+    size_t extlen = strlen(ext);
+    if (would_wrap_around(dirlen, filelen, extlen))
+        return NULL;
+    char *path = malloc(dirlen + SLASH_LEN + filelen + DOT_LEN + extlen + NULL_LEN);
+    if (path == NULL)
+        return NULL; // malloc() failed. Do not continue.
+    fill_buffer(dir, dirlen, fname, filelen, ext, extlen, path);
+    return path;
+}
+
+int main()
+{
+    char *c = make_pathname("ddddddddddddd", "ff", "xx");
+    printf("%s", c);
+    free(c);
+
+    // TEST WRAP CHECK
+    // size_t dirlen = 18446744073709551595UL;
+    // size_t filelen = 9;
+    // size_t extlen = 16;
+    // bool res = would_wrap_around(dirlen, filelen, extlen);
+    // printf("%d\n", res);
+}
\ No newline at end of file