libc: Add strftime()

libc/CMakeLists.txt

@@ -7,6 +7,7 @@ set(SOURCES
     src/unistd.cpp
     src/errno.cpp
     src/string.cpp
+    src/strftime.cpp
     src/fcntl.cpp
     src/assert.cpp
     src/atexit.cpp

libc/include/time.h

@@ -42,6 +42,9 @@ extern "C"
     /* Build a string representation of UNIX time. */
     char* ctime_r(const time_t* tp, char buf[26]);
 
+    /* Format a string representation of broken-down time using a format string. */
+    size_t strftime(char* buf, size_t max, const char* format, const struct tm* tm);
+
 #ifdef __cplusplus
 }
 #endif

libc/src/strftime.cpp

@@ -0,0 +1,140 @@
+#include <luna/Check.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+struct strftime_state
+{
+    char* const buf;
+    const size_t max;
+    size_t pos;
+};
+
+static bool try_put_char(strftime_state& state, char c)
+{
+    if (state.pos == state.max) return false;
+
+    state.buf[state.pos++] = c;
+
+    return true;
+}
+
+static bool try_put_string(strftime_state& state, const char* s)
+{
+    if (state.pos + strlen(s) == (state.max - 1)) return false;
+
+    memcpy(state.buf + state.pos, s, strlen(s));
+
+    state.pos += strlen(s);
+
+    return true;
+}
+
+static bool try_format(strftime_state& state, const char* format, ...)
+{
+    va_list ap;
+    va_start(ap, format);
+
+    char buf[1024];
+    vsnprintf(buf, sizeof(buf), format, ap);
+
+    va_end(ap);
+
+    return try_put_string(state, buf);
+}
+
+static const char* abday_names[] = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };
+static const char* day_names[] = { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" };
+static const char* abmon_names[] = {
+    "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
+};
+static const char* mon_names[] = { "January", "February", "March",     "April",   "May",      "June",
+                                   "July",    "August",   "September", "October", "November", "December" };
+
+extern "C"
+{
+    size_t strftime(char* buf, size_t max, const char* format, const struct tm* tm)
+    {
+        strftime_state state = { .buf = buf, .max = max, .pos = 0 };
+
+        while (*format)
+        {
+            if (*format != '%')
+            {
+                if (!try_put_char(state, *format)) return 0;
+
+                format++;
+                continue;
+            }
+            else
+            {
+                format++;
+                switch (*format)
+                {
+                case 'a':
+                    if (!try_put_string(state, abday_names[tm->tm_wday])) return 0;
+                    break;
+                case 'A':
+                    if (!try_put_string(state, day_names[tm->tm_wday])) return 0;
+                    break;
+                case 'b':
+                    if (!try_put_string(state, abmon_names[tm->tm_mon])) return 0;
+                    break;
+                case 'B':
+                    if (!try_put_string(state, mon_names[tm->tm_mon])) return 0;
+                    break;
+                case 'c': todo();
+                case 'd':
+                    if (!try_format(state, "%.2d", tm->tm_mday)) return 0;
+                    break;
+                case 'H':
+                    if (!try_format(state, "%.2d", tm->tm_hour)) return 0;
+                    break;
+                case 'I': {
+                    int hour = tm->tm_hour % 12;
+                    if (hour == 0) hour = 12;
+                    if (!try_format(state, "%.2d", hour)) return 0;
+                    break;
+                }
+                case 'j': todo();
+                case 'm':
+                    if (!try_format(state, "%.2d", tm->tm_mon + 1)) return 0;
+                    break;
+                case 'M':
+                    if (!try_format(state, "%.2d", tm->tm_min)) return 0;
+                    break;
+                case 'p':
+                    if (tm->tm_hour >= 12)
+                    {
+                        if (!try_put_string(state, "PM")) return 0;
+                    }
+                    else
+                    {
+                        if (!try_put_string(state, "AM")) return 0;
+                    }
+                    break;
+                case 'S':
+                    if (!try_format(state, "%.2d", tm->tm_sec)) return 0;
+                    break;
+                case 'x': todo();
+                case 'X': todo();
+                case 'y':
+                    if (!try_format(state, "%.2d", (tm->tm_year + 1900) % 100)) return 0;
+                    break;
+                case 'Y':
+                    if (!try_format(state, "%d", tm->tm_year + 1900)) return 0;
+                    break;
+                default: fprintf(stderr, "strftime: unexpected conversion specifier %%%c\n", *format); exit(255);
+                }
+
+                format++;
+                continue;
+            }
+        }
+
+        state.buf[state.pos] = '\0';
+
+        return state.pos;
+    }
+}

libc/src/time.cpp

@@ -85,9 +85,6 @@ static void time_to_struct_tm(time_t time, struct tm* result)
     result->tm_sec = (int)time;
 }
 
-const char* wday_names[] = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };
-const char* month_names[] = { "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" };
-
 extern "C"
 {
     int clock_gettime(clockid_t id, struct timespec* ts)
@@ -132,8 +129,7 @@ extern "C"
 
     char* asctime_r(const struct tm* tm, char buf[26])
     {
-        string_format(buf, 26, "%s %s %.2d %.2d:%.2d:%.2d %4d\n", wday_names[tm->tm_wday], month_names[tm->tm_mon],
-                      tm->tm_mday, tm->tm_hour, tm->tm_min, tm->tm_sec, tm->tm_year + 1900);
+        strftime(buf, 26, "%a %b %d %H:%M:%S %Y\n", tm);
         return buf;
     }