libgo/runtime/go-strslice.c

   1 /* go-strslice.c -- the go string slice function.
   2
   3    Copyright 2009 The Go Authors. All rights reserved.
   4    Use of this source code is governed by a BSD-style
   5    license that can be found in the LICENSE file.  */
   6
   7 #include "runtime.h"
   8
   9 String
  10 __go_string_slice (String s, intgo start, intgo end)
  11 {
  12   intgo len;
  13   String ret;
  14
  15   len = s.len;
  16   if (end == -1)
  17     end = len;
  18   if (start > len || end < start || end > len)
  19     runtime_panicstring ("string index out of bounds");
  20   ret.len = end - start;
  21   // If the length of the new string is zero, the str field doesn't
  22   // matter, so just set it to nil.  This avoids the problem of
  23   // s.str + start pointing just past the end of the string,
  24   // which may keep the next memory block alive unnecessarily.
  25   if (ret.len == 0)
  26     ret.str = nil;
  27   else
  28     ret.str = s.str + start;
  29   return ret;
  30 }