commit for once

1 files changed, 25 insertions, 0 deletions

diff --git a/3/7_procedures/35_rfun.c b/3/7_procedures/35_rfun.c
new file mode 100644
index 0000000..f923366
--- /dev/null
+++ b/3/7_procedures/35_rfun.c
@@ -0,0 +1,25 @@
+// x in %rdi
+// rfun:
+//      pushq %rbx          save rbx, since we use it and in case we are called
+//      movq %rdi, %rbx     %rbx <- x
+//      movl $0             %rax <- 0
+//      testq %rdi, %rdi    ZF <- %rdi == 0
+//      je .L2              jump to if ZF
+//      shrq $2, %rdi       shift x to the lift by 2 bits (divide by four)
+//      call rfun
+//      addq %rbx, %rax     add our calculation to the rest
+//  .L2
+//      popq %rbx           set rbx back to the value of our caller's calculation
+//      ret
+//
+//  A>
+//      The value x is stored in rbx, and each iteration stores (int64_t) x/4
+//  B>
+long rfun(unsigned long x) {
+    if (x == 0) {
+        return 0;
+    }
+    unsigned long nx = x>>2;
+    long rv = rfun(nx);
+    return x + rv;
+}