Implemented strcmp() and strlen()

doc/contents/datetime.tex

@@ -2,7 +2,7 @@
 \section{Timekeeping API}
 Provide calendar dates and clock time based on the on-chip RTC.
 
-\subsection*{Overview}
+\paragraph{Overview}
 \begin{itemize}
     \item Reads a 32-bit seconds-since-1970 counter (RTC register at `0x101e8000`).
     \item Exposes two APIs:
@@ -35,30 +35,30 @@ \subsection*{Data Structure}
 Data Register(\textbf{RTCDR}). This is a 32 bit register, and therefore 
 \underline{subject to the Year 2038 Problem}.
 
-\subsection{API: \texttt{uint32\_t getdate(dateval *date\_struct)}}
+\subsection{\texttt{uint32\_t getdate(dateval *date\_struct)}}
 Populate the provided \texttt{*date\_struct} with the current date in days, months, and years.
 
-\subsubsection*{Parameters}
+\paragraph{Parameters}
 \begin{itemize}
     \item \texttt{date\_struct} pointer to a \texttt{dateval} structure; if \texttt{NULL}, 
     only the raw \textbf{RTC} counter is returned.
 \end{itemize}
 
-\subsubsection*{Return Value}
+\paragraph{Return Value}
 \begin{itemize}
     \item Returns number of seconds since epoch (\texttt{RTCDR}) as read from the hardware register.
 \end{itemize}
 
-\subsection{API: \texttt{uint32\_t gettime(timeval *time\_struct)}}
+\subsection{\texttt{uint32\_t gettime(timeval *time\_struct)}}
 Populate \texttt{*time\_struct} with the current click time in hours, minutes, and seconds.
 
-\subsubsection*{Parameters}
+\paragraph{Parameters}
 \begin{itemize}
     \item \texttt{time\_struct} pointer to a \texttt{timeval} structure; if \texttt{NULL}, 
     only the raw \textbf{RTC} counter is returned.
 \end{itemize}
 
-\subsubsection*{Return Value}
+\paragraph{Return Value}
 \begin{itemize}
     \item Returns number of seconds since epoch (\texttt{RTCDR}) as read from the hardware register.
 \end{itemize}

doc/contents/puts.tex → doc/contents/print.tex

@@ -1,41 +1,45 @@
 % ------------------------------------------------
-% *** Section 2: I/O API ***
+% *** Section 2: I/O \& Time Services ***
 % ------------------------------------------------
 \newpage
 \chapter{I/O \& Time Services}
 
-\section{UART Device Driver}
+\section{UART Output API}
+
 \subsubsection{Registers \& Constants}
 \begin{itemize}
   \item \textbf{UART0\_DR} (Data Register), \texttt{0x101f1000}
   \item \textbf{UART0\_FR} (Flag Register), \texttt{0x101f1018}
   \item \textbf{UART\_FR\_TXFF}, \textbf{UART\_FR\_RXFE}
 \end{itemize}
 
-\subsection{API: \texttt{printf(char *s, ...)}}
+\subsection{\texttt{printf(char *s, ...)}}
+
+\paragraph{Description}
 Sends a null-terminated format string over UART. If an incorrect datatype is given 
 for a format specifier, \underline{the behavior is undefined}. If a format specifier 
 is given without a matching argument, it is simply skipped when the string is outputted. 
 The following format specifiers are supported:
 
+\paragraph{Supported Format Specifiers}
 \begin{itemize}
-  \item \textbf{\%c}: Expects a single character.
-  \item \textbf{\%s}: Expects a null-terminated string.
-  \item \textbf{\%d}: For 32-bit signed integers in the range \texttt{-2147483648} to \texttt{2147483647}.
-  \item \textbf{\%ld}: For 64-bit signed integers in the range \texttt{-9223372036854775808} to \texttt{9223372036854775807}, excluding the range specified above, for \textbf{\%d}.
-  \item \textbf{\%lu}: For 64-bit unsigned integers in the range \texttt{2147483648} to \texttt{18446744073709551615}.
-  \item \textbf{\%x} and \textbf{\%X}: For 32-bit unsigned integers in the range \texttt{0} to \texttt{2147483647}, where the case of \texttt{x} determines the case of the hexadecimal digits (\texttt{a-f} or \texttt{A-F}).
-  \item \textbf{\%lx} and \textbf{\%lX}: For 64-bit unsigned integers printed in hexadecimal format. Has the same range as \textbf{\%lu}. The case of \texttt{x} determines the case of the hexadecimal digits (\texttt{a-f} or \texttt{A-F}).
-  \item \textbf{\%\%}: Outputs a '\%'.
-  \item \textbf{\%}: Outputs (null). This is a special case where the format specifier is not followed by any character, and it simply outputs nothing.
+  \item \texttt{\%c}: Expects a single character.
+  \item \texttt{\%s}: Expects a null-terminated string.
+  \item \texttt{\%d}: For 32-bit signed integers in the range \texttt{-2147483648} to \texttt{2147483647}.
+  \item \texttt{\%ld}: For 64-bit signed integers in the range \texttt{-9223372036854775808} to \texttt{9223372036854775807}, excluding the range specified above, for \textbf{\%d}.
+  \item \texttt{\%lu}: For 64-bit unsigned integers in the range \texttt{2147483648} to \texttt{18446744073709551615}.
+  \item \texttt{\%x}, \texttt{\%X}: For 32-bit unsigned integers in the range \texttt{0} to \texttt{2147483647}, where the case of \texttt{x} determines the case of the hexadecimal digits (\texttt{a-f} or \texttt{A-F}).
+  \item \texttt{\%lx}, \texttt{\%lX}: For 64-bit unsigned integers printed in hexadecimal format. Has the same range as \textbf{\%lu}. The case of \texttt{x} determines the case of the hexadecimal digits (\texttt{a-f} or \texttt{A-F}).
+  \item \texttt{\%\%}: Outputs a literal \texttt{\%}.
+  \item \texttt{\%}: If the format specifier is not followed by a valid character, prints \texttt{(null)}.
 \end{itemize}
 
 \begin{flushleft}
 All the ranges specified above are inclusive. Also, note that integers in the 
 range \texttt{-2147483648} to \texttt{2147483647} are passed as 32 bit integers 
 and any integers not part of this range are passed as 64 bit integers \underline{by default}.
 If desired, integers of this range can be cast as \texttt{long long} or \texttt{unsigned long long} 
-for use with the format specifiers prefixed by \textbf{l}(ell).
+for use with the format specifiers prefixed by the character \texttt{l}.
 \end{flushleft}
 
 \subsection*{Examples}

doc/contents/string.tex

@@ -0,0 +1,71 @@
+\newpage
+\section{String Manipulation API}
+\subsection{\texttt{strcmp(const char *str\_1, const char *str\_2)}}
+
+\paragraph{Purpose}
+Compares two null-terminated strings, character by character.
+
+\paragraph{Overview}
+This function compares the characters of two strings (\texttt{ASCII values}), 
+\texttt{str\_1} and \texttt{str\_2}, one by one. It returns:
+
+\paragraph{Return Values}
+\begin{itemize}
+    \item 0 if both strings are equal,
+    \item -1 if the first differing character in \texttt{str\_1} is less than that in \texttt{str\_2},
+    \item 1 if the first differing character in \texttt{str\_1} is greater than that in \texttt{str\_2}.
+\end{itemize}
+
+\paragraph{Behavior}
+The comparison stops at the first difference or the null terminator. 
+Case sensitivity is observed. Behavior is undefined if either pointer is not a 
+valid null-terminated string.
+
+\subsection*{Examples}
+\begin{lstlisting}[language=C, caption=String Comparison Example]
+  int result = strcmp("abc", "abc"); // Expect 0
+  printf("Expect 0 -> %d\n", result);
+
+  result = strcmp("abc", "abd"); // Expect -1
+  printf("Expect -1 -> %d\n", result);
+
+  result = strcmp("abc", "ABC"); // Expect 1
+  printf("Expect 1 -> %d\n", result);
+\end{lstlisting}
+
+\begin{note}
+In the future, we could returning the difference between the first differing 
+characters, which would allow for more detailed comparisons. This would enable 
+users to understand how far apart the strings are in terms of character values.
+\end{note}
+
+\subsection{\texttt{strlen(const char *str)}}
+
+\paragraph{Purpose}
+Calculates the length of a null-terminated string.
+
+\paragraph{Overview}
+This function counts the number of characters in a null-terminated string,
+excluding the null terminator itself. It returns the length of the string as an
+unsigned integer. This function uses pointer arithmetic to traverse the string, 
+performing mathematical operations directly on the pointer values.
+
+\paragraph{Return Values}
+\begin{itemize}
+    \item The number of characters in the string, not including the null terminator.
+    \item 0 if the string is empty (i.e., the first character is the null terminator).
+\end{itemize}
+
+\paragraph{Behavior}
+The function iterates through the input string until the null terminator is found, returning 
+the number of characters preceding it. If the input pointer is not a valid 
+null-terminated string, the behavior is undefined.
+
+\subsection*{Examples}
+\begin{lstlisting}[language=C, caption=String Length Example]
+  size_t result = strlen("abc"); // Expect 3
+  printf("Expect len 3 -> %d\n", result);
+
+  result = strlen(""); // Expect 0
+  printf("Expect len 0 -> %d\n", result);
+\end{lstlisting}

doc/front/preface.tex

@@ -41,7 +41,7 @@ \section*{Preface}
 
 \addcontentsline{toc}{section}{About This Project}
 \section*{About This Project}
-\subsection*{Resources}
+\paragraph{Resources}
 
 To guide my learning and support development of AstraKernel, I am using the following resources, 
 which are particularly valuable for foundational and practical understanding of OS design:
@@ -50,26 +50,28 @@ \subsection*{Resources}
   \item \textbf{The Little Book About OS Development} by Erik Helin and Adam Renberg
 \end{itemize}
 
-\subsection*{Acknowledgments \& Contributions}
+\paragraph{Contributions}
 
 AstraKernel is an open source project, and I encourage contributions from anyone 
 interested in improving, extending the kernel or simply experiment with it. I also 
 encourage anyone to improve this documentation, as it is a work in progress.
 If you would like to contribute, please feel free to open an issue or pull request on the GitHub repository.
+\\
 \begin{info}
   You can join the Matrix Server \url{https://matrix.to/#/#sandboxscience:matrix.org} 
   for general SandBox Science discussion as well as project-specific discussion such 
   as AstraKernel development.
 \end{info}
 
-\noindent
+\paragraph{Acknowledgments}
 Specially thanks to the following individuals for their contributions:
 \begin{itemize}
-  \item \textbf{shade5144} (\url{https://github.com/shade5144}) for contributing the initial version of the \texttt{printf} 
-  function as well as the documentation for it.
+  \item \textbf{shade5144} (\url{https://github.com/shade5144}) for contributing 
+  the initial version of the \texttt{printf} and \texttt{datetime} function as 
+  well as the documentation for them.
 \end{itemize}
 
-\subsection*{Disclaimer}
+\paragraph{Disclaimer}
 
 AstraKernel is currently in its early stages of development and is not intended for production use. 
 It is primarily an educational and experimental project. The code is provided as-is, 

doc/main.tex

@@ -18,7 +18,8 @@
 % % *** Main Content ***
 % % -----------------------------------------------------
 \input{contents/introduction}
-\input{contents/puts}
+\input{contents/print}
+\input{contents/string}
 \input{contents/datetime}
 
 \end{document}

include/string.h

@@ -0,0 +1,18 @@
+#ifndef STRING_H
+#define STRING_H
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+  int strcmp(const char *str_1, const char *str_2);
+  size_t strlen(const char *str);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // STRING_H

kernel/kernel.c

@@ -4,6 +4,7 @@
 #include "datetime.h"
 #include "printf.h"
 #include "clear.h"
+#include "string.h"
 
 static const char *banner[] = {
     "========================================\r\n",
@@ -53,37 +54,50 @@ void kernel_main(void)
 
         switch (input_buffer[0])
         {
-        case 'h': // Check for help command
-            printf("\nHelp:\n 'q' to exit\n 'h' for help\n 'c' to clear screen\n 't' to print current time\n 'd' to print current date\r\n");
-            break;
-        case 'e': // TODO: This is for testing purposes. Remove once not needed
-            printf("%ld %ld %ld\n", 0, -9223372036854775808, 9223372036854775807);
-            printf("%d %d\n", 2147483647, -2147483648);
-            printf("%x %lx %lX %X\n", 2147483647, 2147483649, 2147483648, 1234);
-            printf("%lX %x %lx\n", 0x123456789abcdef0, 1234, 9223372036854775809);
-            printf("Name: %c\n", 'b');
-            printf("Hello %s\n", "World");
-            printf("100%%\n");
-            break;
-        case 'q': // Check for exit command
-            printf("Exiting...\r\n");
-            is_running = false;
-            break;
-        case 'c': // Check for clear screen command
-            clear();
-            break;
-
-        case 't': // Check for time command
-            gettime(&time_struct);
-            printf("Current time(GMT): %d:%d:%d\n", time_struct.hrs, time_struct.mins, time_struct.secs);
-            break;
-        case 'd': // Check for date command
-            getdate(&date_struct);
-            printf("Current date(MM-DD-YYYY): %d-%d-%d\n", date_struct.month, date_struct.day, date_struct.year);
-            break;
-        default:
-            printf("Unknown command. Type 'h' for help.\r\n");
-            break;
+            case 'h': // Check for help command
+                printf("\nHelp:\n 'q' to exit\n 'h' for help\n 'c' to clear screen\n 't' to print current time\n 'd' to print current date\r\n");
+                break;
+            case 'e':
+                int result = strcmp("abc", "abc"); // Expect 0
+                printf("Expect 0 -> %d\n", result);
+
+                result = strcmp("abc", "abd"); // Expect -1
+                printf("Expect -1 -> %d\n", result);
+
+                result = strcmp("abc", "ABC"); // Expect 1
+                printf("Expect 1 -> %d\n", result);
+
+                result = strcmp("ABC", "abc"); // Expect -1
+                printf("Expect -1 -> %d\n", result);
+
+                result = strcmp("\x01\x02\x03", "\x01\x02\x03"); // Expect 0
+                printf("Expect 0 -> %d\n", result);
+
+                result = strcmp("\x01\x02\x03", "\x01\x02\x04"); // Expect -1
+                printf("Expect -1 -> %d\n", result);
+
+                result = strcmp("\x01\x02\x04", "\x01\x02\x03"); // Expect 1
+                printf("Expect 1 -> %d\n", result);
+                break;
+            case 'q': // Check for exit command
+                printf("Exiting...\r\n");
+                is_running = false;
+                break;
+            case 'c': // Check for clear screen command
+                clear();
+                break;
+
+            case 't': // Check for time command
+                gettime(&time_struct);
+                printf("Current time(GMT): %d:%d:%d\n", time_struct.hrs, time_struct.mins, time_struct.secs);
+                break;
+            case 'd': // Check for date command
+                getdate(&date_struct);
+                printf("Current date(MM-DD-YYYY): %d-%d-%d\n", date_struct.month, date_struct.day, date_struct.year);
+                break;
+            default:
+                printf("Unknown command. Type 'h' for help.\r\n");
+                break;
         }
     }
 }

user/string.c

@@ -0,0 +1,45 @@
+#include "string.h"
+
+/**
+ * @brief Compares two null-terminated strings lexicographically.
+ *
+ * @param str_1 Pointer to the first string to compare.
+ * @param str_2 Pointer to the second string to compare.
+ * 
+ * @return int 0 if strings are equal, -1 if `str_1` < `str_2`, 1 if `str_1` > `str_2`.
+ */
+int strcmp(const char *str_1, const char *str_2)
+{
+  unsigned char ch1, ch2;
+  do
+  {
+    ch1 = *str_1++;
+    ch2 = *str_2++;
+
+    if (ch1 != ch2)
+    {
+      // NOTE: If needed in the future, can return the difference between
+      // the strings rather than just -1 or 1
+      return ch1 < ch2 ? -1 : 1;
+    }
+
+  } while (ch1);
+
+  return 0;
+}
+
+/**
+ * @brief Calculates the length of a null-terminated string.
+ *
+ * @param str Pointer to the null-terminated string to be measured.
+ * @return The number of characters in the string, excluding the null terminator.
+ */
+size_t strlen(const char *str)
+{
+  const char *s = str;
+  while (*s)
+  {
+    ++s;
+  }
+  return s - str;
+}