1 files changed, 95 insertions, 0 deletions
diff --git a/user/printf.c b/user/printf.c
new file mode 100644
index 0000000..0c6b34b
--- /dev/null
+++ b/user/printf.c
@@ -0,0 +1,95 @@
+#include "kernel/types.h"
+#include "kernel/stat.h"
+#include "user/user.h"
+
+#include <stdarg.h>
+
+static char digits[] = "0123456789ABCDEF";
+
+static void
+putc(int fd, char c)
+{
+  write(fd, &c, 1);
+}
+
+static void
+printint(int fd, int xx, int base, int sgn)
+{
+  char buf[16];
+  int i, neg;
+  uint x;
+
+  neg = 0;
+  if(sgn && xx < 0){
+    neg = 1;
+    x = -xx;
+  } else {
+    x = xx;
+  }
+
+  i = 0;
+  do{
+    buf[i++] = digits[x % base];
+  }while((x /= base) != 0);
+  if(neg)
+    buf[i++] = '-';
+
+  while(--i >= 0)
+    putc(fd, buf[i]);
+}
+
+static void
+printptr(int fd, uint64 x) {
+  int i;
+  putc(fd, '0');
+  putc(fd, 'x');
+  for (i = 0; i < (sizeof(uint64) * 2); i++, x <<= 4)
+    putc(fd, digits[x >> (sizeof(uint64) * 8 - 4)]);
+}
+
+// Print to the given fd. Only understands %d, %x, %p, %s.
+void
+printf(int fd, const char *fmt, ...)
+{
+  va_list ap;
+  char *s;
+  int c, i, state;
+
+  va_start(ap, fmt);
+  state = 0;
+  for(i = 0; fmt[i]; i++){
+    c = fmt[i] & 0xff;
+    if(state == 0){
+      if(c == '%'){
+        state = '%';
+      } else {
+        putc(fd, c);
+      }
+    } else if(state == '%'){
+      if(c == 'd'){
+        printint(fd, va_arg(ap, int), 10, 1);
+      } else if(c == 'x') {
+        printint(fd, va_arg(ap, int), 16, 0);
+      } else if(c == 'p') {
+        printptr(fd, va_arg(ap, uint64));
+      } else if(c == 's'){
+        s = va_arg(ap, char*);
+        if(s == 0)
+          s = "(null)";
+        while(*s != 0){
+          putc(fd, *s);
+          s++;
+        }
+      } else if(c == 'c'){
+        putc(fd, va_arg(ap, uint));
+      } else if(c == '%'){
+        putc(fd, c);
+      } else {
+        // Unknown % sequence.  Print it to draw attention.
+        putc(fd, '%');
+        putc(fd, c);
+      }
+      state = 0;
+    }
+  }
+}