--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/uprogs/printf.c	Sun Jan 06 19:27:03 2019 +0900
@@ -0,0 +1,103 @@
+#include "types.h"
+#include "stat.h"
+#include "user.h"
+
+static void
+putc(int fd, char c)
+{
+  write(fd, &c, 1);
+}
+
+u32 div(u32 n, u32 d)  // long division
+{
+    u32 q=0, r=0;
+    int i;
+
+    for(i=31;i>=0;i--){
+        r = r << 1;
+        r = r | ((n >> i) & 1);
+        if(r >= d) {
+            r = r - d;
+            q = q | (1 << i);
+        }
+    }
+    return q;
+}
+
+static void
+printint(int fd, int xx, int base, int sgn)
+{
+  static char digits[] = "0123456789ABCDEF";
+  char buf[16];
+  int i, neg;
+  uint x, y, b;
+
+  neg = 0;
+  if(sgn && xx < 0){
+    neg = 1;
+    x = -xx;
+  } else {
+    x = xx;
+  }
+
+  b = base;
+  i = 0;
+  do{
+    y = div(x, b);
+    buf[i++] = digits[x - y * b];
+  }while((x = y) != 0);
+  if(neg)
+    buf[i++] = '-';
+
+  while(--i >= 0)
+    putc(fd, buf[i]);
+}
+
+// Print to the given fd. Only understands %d, %x, %p, %s.
+void
+printf(int fd, char *fmt, ...)
+{
+  char *s;
+  int c, i, state;
+  uint *ap;
+
+  state = 0;
+  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'){
+        s = (char*)*ap;
+        ap++;
+        if(s == 0)
+          s = "(null)";
+        while(*s != 0){
+          putc(fd, *s);
+          s++;
+        }
+      } else if(c == 'c'){
+        putc(fd, *ap);
+        ap++;
+      } else if(c == '%'){
+        putc(fd, c);
+      } else {
+        // Unknown % sequence.  Print it to draw attention.
+        putc(fd, '%');
+        putc(fd, c);
+      }
+      state = 0;
+    }
+  }
+}