From c3b737037ad668ef841ed163ebd9fee81bb0453e Mon Sep 17 00:00:00 2001
From: Yuichi Nishiwaki <yuichi.nishiwaki@gmail.com>
Date: Sun, 30 Mar 2014 14:45:24 +0900
Subject: [PATCH] refactor native_stack_length

---
 include/picrin/cont.h | 2 +-
 src/cont.c            | 7 ++++---
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/picrin/cont.h b/include/picrin/cont.h
index 0367bb14..494e042a 100644
--- a/include/picrin/cont.h
+++ b/include/picrin/cont.h
@@ -16,7 +16,7 @@ struct pic_cont {
   pic_block *blk;
 
   char *stk_pos, *stk_ptr;
-  size_t stk_len;
+  ptrdiff_t stk_len;
 
   pic_value *st_ptr;
   size_t sp_offset, st_len;
diff --git a/src/cont.c b/src/cont.c
index 6248a503..70647fb8 100644
--- a/src/cont.c
+++ b/src/cont.c
@@ -77,7 +77,7 @@ pic_receive(pic_state *pic, size_t n, pic_value *argv)
 static void save_cont(pic_state *, struct pic_cont **);
 static void restore_cont(pic_state *, struct pic_cont *);
 
-static size_t
+static ptrdiff_t
 native_stack_length(pic_state *pic, char **pos)
 {
   char t;
@@ -87,8 +87,8 @@ native_stack_length(pic_state *pic, char **pos)
     : pic->native_stack_start;
 
   return (pic->native_stack_start > &t)
-    ? (size_t)(pic->native_stack_start - &t)
-    : (size_t)(&t - pic->native_stack_start + 1);
+    ? pic->native_stack_start - &t
+    : &t - pic->native_stack_start;
 }
 
 static void
@@ -106,6 +106,7 @@ save_cont(pic_state *pic, struct pic_cont **c)
   cont->stk_pos = pos;
   cont->stk_ptr = pic_alloc(pic, sizeof(pic_value) * cont->stk_len);
   memcpy(cont->stk_ptr, cont->stk_pos, sizeof(pic_value) * cont->stk_len);
+  assert(cont->stk_len > 0);
 
   cont->sp_offset = pic->sp - pic->stbase;
   cont->st_len = pic->stend - pic->stbase;