From 50dc3e7d9f4f290c7353313c5e5f888cb7c4846d Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Wed, 8 May 2019 10:35:02 -0700
Subject: [PATCH] Add hb_iota()

---
 src/hb-iter.hh   | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 src/test-iter.cc | 10 ++++++++++
 2 files changed, 61 insertions(+)

diff --git a/src/hb-iter.hh b/src/hb-iter.hh
index 23d2c27..1a3e2ab 100644
--- a/src/hb-iter.hh
+++ b/src/hb-iter.hh
@@ -570,6 +570,57 @@ struct
 }
 HB_FUNCOBJ (hb_apply);
 
+/* hb_iota() */
+
+template <typename T, typename S>
+struct hb_iota_iter_t :
+  hb_iter_t<hb_iota_iter_t<T, S>, T>
+{
+  hb_iota_iter_t (T start, T end, S step) : v (start), end (end_for (start, end, step)), step (step) {}
+
+  typedef T __item_t__;
+  static constexpr bool is_random_access_iterator = true;
+  static constexpr bool is_sorted_iterator = true;
+  __item_t__ __item__ () const { return v; }
+  __item_t__ __item_at__ (unsigned j) const { return v + j * step; }
+  bool __more__ () const { return v != end; }
+  unsigned __len__ () const { return (end - v) / step; }
+  void __next__ () { v += step; }
+  void __forward__ (unsigned n) { v += n * step; }
+  void __prev__ () { v -= step; }
+  void __rewind__ (unsigned n) { v -= n * step; }
+  hb_iota_iter_t __end__ () const { hb_iota_iter_t (end, end, step); }
+  bool operator != (const hb_iota_iter_t& o) const
+  { return v != o.v || end != o.end || step != o.step; }
+
+  private:
+  static inline T end_for (T start, T end, S step)
+  {
+    auto res = (end - start) % step;
+    if (!res)
+      return end;
+    end += step - res;
+    return end;
+  }
+
+  private:
+  T v;
+  T end;
+  S step;
+};
+struct
+{
+  template <typename T = unsigned> hb_iota_iter_t<T, unsigned>
+  operator () (T end = (unsigned) -1) const
+  { return hb_iota_iter_t<T, unsigned> (0, end, 1u); }
+
+  template <typename T, typename S = unsigned> hb_iota_iter_t<T, S>
+  operator () (T start, T end, S&& step = 1u) const
+  { return hb_iota_iter_t<T, S> (start, end, step); }
+}
+HB_FUNCOBJ (hb_iota);
+
+
 /* hb_sink() */
 
 template <typename Sink>
diff --git a/src/test-iter.cc b/src/test-iter.cc
index fe3c8f3..f29166f 100644
--- a/src/test-iter.cc
+++ b/src/test-iter.cc
@@ -236,5 +236,15 @@ main (int argc, char **argv)
   long vl;
   s >> vl;
 
+  hb_iota ();
+  assert (hb_iota (9).len () == 9);
+  assert (hb_iota (2, 9).len () == 7);
+  assert (hb_iota (2, 9, 3).len () == 3);
+  assert (hb_iota (2, 8, 3).len () == 2);
+  assert (hb_iota (2, 7, 3).len () == 2);
+  assert (hb_iota (-2, -9, -3).len () == 3);
+  assert (hb_iota (-2, -8, -3).len () == 2);
+  assert (hb_iota (-2, -7, -3).len () == 2);
+
   return 0;
 }
-- 
2.7.4