1 files changed, 76 insertions, 0 deletions
diff --git a/printf.c b/printf.c
new file mode 100644
index 0000000..0d42236
--- /dev/null
+++ b/printf.c
@@ -0,0 +1,76 @@
+#include "user.h"
+#include "types.h"
+
+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];
+  char digits[] = "0123456789ABCDEF";
+  int i = 0, neg = 0;
+  uint x;
+  
+  if(sgn && xx < 0){
+    neg = 1;
+    x = 0 - xx;
+  } else {
+    x = xx;
+  }
+
+  do {
+    buf[i++] = digits[x % base];
+  } while((x /= base) != 0);
+  if(neg)
+    buf[i++] = '-';
+
+  while(--i >= 0)
+    putc(fd, buf[i]);
+}
+
+/*
+ * printf to the stdout. only understands %d, %x, %p, %s.
+ */
+void
+printf(int fd, char *fmt, ...)
+{
+  int i, state = 0, c;
+  uint *ap = (uint *)(void*)&fmt + 1;
+
+  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, *ap, 10, 1);
+        ap++;
+      } else if(c == 'x' || c == 'p'){
+        printint(fd, *ap, 16, 0);
+        ap++;
+      } else if(c == 's'){
+        char *s = (char*)*ap;
+        ap++;
+        while(*s != 0){
+          putc(fd, *s);
+          s++;
+        }
+      } else if(c == '%'){
+        putc(fd, c);
+      } else {
+        // Unknown % sequence.  Print it to draw attention.
+        putc(fd, '%');
+        putc(fd, c);
+      }
+      state = 0;
+    }
+  }
+}