Added documentation for boot_sprintf

Author: ZERICO2005

docs/headers/boot_sprintf.rst

@@ -0,0 +1,76 @@
+.. _boot_sprintf:
+
+boot_sprintf
+======================
+
+.. code-block:: c
+
+    #include <boot_sprintf.h>
+
+The OS comes with an implementation of ANSI C89 `sprintf`, which can reduce the size of a program by ~8 KiB. However, it is very limited in functionality. It does not support width specifiers, and it won't accept :code:`long` or :code:`float` arguments.
+
+The following type specifiers are supported :code:`%s %c %d %i %u %o %x %X %p %n`, alongside the flags :code:`-+ #0*` in addition to the width field.
+
+All length modifiers :code:`hh h l ll j z t L` and floating point specifiers :code:`%f %g %e %a` are **not** supported.
+
+Additionally, each individual argument will write no more than 255 characters each. This means that any strings written with :code:`%s` will be truncated after 255 characters.
+
+The :code:`<boot_sprintf.h>` header provides `boot_sprintf`. `boot_snprintf` and `boot_asprintf` are also provided as macros
+
+.. code-block:: c
+
+    int boot_sprintf(char *restrict buffer, const char *restrict format, ...)
+
+    int boot_snprintf(char *buffer, size_t count, const char *restrict format, ...)
+
+    int boot_asprintf(char **restrict p_buffer, const char *restrict format, ...)
+
+Because the OS does not provide `vsprintf`, `boot_snprintf` and `boot_asprintf` are implemented as macros. This means that :code:`...` or :code:`__VA_ARGS__` will be evaluated twice when the macro is expanded. `sprintf` is traditionally "unsafe" because a maximum output length cannot be specified, which can cause buffer overflows. By writing to an unmapped memory address :code:`0xE40000`, `boot_sprintf` can safely write up to ~786000 bytes which can then be used to determine the length of the output.
+
+replacing printf functions
+----------------------------
+
+To disable all other printf functions with `boot_sprintf`, `boot_snprintf`, and `boot_asprintf`, add the following line to the Makefile. More information `here <https://ce-programming.github.io/toolchain/static/printf.html>`
+
+.. code-block:: makefile
+
+    HAS_PRINTF = NO
+
+.. warning::
+
+    :code:`std::snprintf` and :code:`std::asprintf` will cause errors if :code:`HAS_PRINTF = NO`
+
+boot_asprintf
+----------------------------
+
+`boot_asprintf` functions similarly to `asprintf <https://www.man7.org/linux/man-pages/man3/asprintf.3.html>`_. It will automatically allocate a buffer containing the output from `boot_sprintf`. The buffer shall be deallocated with :code:`free`. The returned buffer will be :code:`NULL` if an allocation or formatting error occurs.
+
+boot_snprintf
+----------------------------
+
+`boot_snprintf` is similar to `snprintf`, except that it returns an empty string if the result of `boot_sprintf` won't fit inside the buffer. Otherwise passing in :code:`boot_snprintf(NULL, 0, format, args)` can be used to query the length of the output without writing to a buffer.
+
+The truncating behavior of C99 `snprintf` can be replicated with `boot_asprintf`
+
+.. code-block:: c
+    char buf[20];
+    char* temp;
+    boot_asprintf(&temp, format, ...);
+    if (temp != NULL) {
+        strncpy(buf, temp, sizeof(buf));
+        buf[sizeof(buf) - 1] = '\0'; // null terminate the end of the buffer
+        free(temp);
+    }
+
+printf and fprintf
+----------------------------
+`printf` and `fprintf` can be replicated by using `boot_asprintf` and `fputs`
+
+.. code-block:: c
+    char* output;
+    boot_asprintf(&output, format, ...);
+    if (output != NULL) {
+        // fprintf(stdout, ...) == printf(...)
+        fputs(stdout, output);
+        free(output);
+    }

docs/static/printf.rst

@@ -11,8 +11,7 @@ However, they contribute around 8 KiB to the resultant program.
 It is highly recommended to not use `printf` and related functions at all because of this.
 If you insist on using these functions, this page details how to do so in the next section.
 
-Alternatively, a limited `sprintf` implementation is baked into the OS which doesn't add any extra size to the resultant program.
-Only the 'c', 'd', 'u', 'x', and 's' format specifiers will probably work.
+Alternatively, a limited `sprintf` (no `long` or `float` support) implementation is baked into the OS which doesn't add any extra size to the resultant program. See the dedicated page for more information `<boot_sprintf.h> <https://ce-programming.github.io/toolchain/headers/boot_sprintf.html>`_.
 To disable all other printf functions and use this `sprintf` implementation, add the following line to the Makefile:
 
 .. code-block:: makefile