stdlib: Implement ivec::unsafe::set_len

Author: pcwalton

src/lib/ioivec.rs

@@ -63,7 +63,7 @@ obj FILE_buf_reader(os::libc::FILE f, bool must_close) {
         auto buf = ~[];
         ivec::reserve[u8](buf, len);
         auto read = os::libc_ivec::fread(ivec::to_ptr[u8](buf), 1u, len, f);
-        ivec::len_set[u8](buf, read);
+        ivec::unsafe::set_len[u8](buf, read);
         ret buf;
     }
     fn read_byte() -> int { ret os::libc::fgetc(f); }

src/lib/ivec.rs

@@ -3,6 +3,7 @@
 import option::none;
 import option::some;
 import uint::next_power_of_two;
+import ptr::addr_of;
 
 type operator2[T,U,V] = fn(&T, &U) -> V;
 
@@ -35,10 +36,6 @@ fn len[T](&T[mutable?] v) -> uint {
     ret rusti::ivec_len(v);
 }
 
-fn len_set[T](&mutable T[mutable?] v, uint new_len) {
-    v = slice(v, 0u, new_len);
-}
-
 type init_op[T] = fn(uint) -> T;
 
 fn init_fn[T](&init_op[T] op, uint n_elts) -> T[] {
@@ -217,6 +214,11 @@ fn find[T](fn(&T) -> bool  f, &T[] v) -> option::t[T] {
 }
 
 mod unsafe {
+    type ivec_repr = rec(mutable uint fill,
+                         mutable uint alloc,
+                         *mutable ivec_heap_part heap_part);
+    type ivec_heap_part = rec(mutable uint fill);
+
     fn copy_from_buf[T](&mutable T[] v, *T ptr, uint count) {
         ret rustrt::ivec_copy_from_buf_shared(v, ptr, count);
     }
@@ -226,5 +228,16 @@ mod unsafe {
         copy_from_buf(v, ptr, bytes);
         ret v;
     }
+
+    fn set_len[T](&mutable T[] v, uint new_len) {
+        auto new_fill = new_len * sys::size_of[T]();
+        let *mutable ivec_repr stack_part =
+            ::unsafe::reinterpret_cast(addr_of(v));
+        if ((*stack_part).fill == 0u) {
+            (*(*stack_part).heap_part).fill = new_fill;     // On heap.
+        } else {
+            (*stack_part).fill = new_fill;                  // On stack.
+        }
+    }
 }
 

src/lib/sys.rs

@@ -1,5 +1,8 @@
 
+import rustrt::size_of;
+
 export rustrt;
+export size_of;
 
 native "rust" mod rustrt {
 
@@ -13,6 +16,7 @@ native "rust" mod rustrt {
     fn do_gc();
     fn unsupervise();
 }
+
 // Local Variables:
 // mode: rust;
 // fill-column: 78;