Initial revision

1 files changed, 79 insertions, 0 deletions

diff --git a/mpf/div_2exp.c b/mpf/div_2exp.c
new file mode 100644
index 000000000..d7296254e
--- /dev/null
+++ b/mpf/div_2exp.c
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+/* mpf_div_2exp -- Divide a float by 2^n.
+
+Copyright (C) 1993, 1994, 1996 Free Software Foundation, Inc.
+
+This file is part of the GNU MP Library.
+
+The GNU MP Library is free software; you can redistribute it and/or modify
+it under the terms of the GNU Library General Public License as published by
+the Free Software Foundation; either version 2 of the License, or (at your
+option) any later version.
+
+The GNU MP Library is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
+License for more details.
+
+You should have received a copy of the GNU Library General Public License
+along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
+the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+MA 02111-1307, USA. */
+
+#include "gmp.h"
+#include "gmp-impl.h"
+
+void
+#if __STDC__
+mpf_div_2exp (mpf_ptr r, mpf_srcptr u, unsigned long int exp)
+#else
+mpf_div_2exp (r, u, exp)
+     mpf_ptr r;
+     mpf_srcptr u;
+     unsigned long int exp;
+#endif
+{
+  mp_srcptr up;
+  mp_ptr rp = r->_mp_d;
+  mp_size_t usize;
+  mp_size_t abs_usize;
+  mp_size_t prec = r->_mp_prec;
+  mp_exp_t uexp = u->_mp_exp;
+
+  usize = u->_mp_size;
+
+  if (usize == 0)
+    {
+      r->_mp_size = 0;
+      r->_mp_exp = 0;
+      return;
+    }
+
+  abs_usize = ABS (usize);
+  up = u->_mp_d;
+
+  if (abs_usize > prec)
+    {
+      up += abs_usize - prec;
+      abs_usize = prec;
+    }
+
+  if (exp % BITS_PER_MP_LIMB == 0)
+    {
+      if (rp != up)
+	MPN_COPY (rp, up, abs_usize);
+      r->_mp_exp = uexp - exp / BITS_PER_MP_LIMB;
+    }
+  else
+    {
+      /* Use mpn_lshift since mpn_rshift operates upwards, and we therefore
+	 would clobber part of U before using that part, when R == U.  */
+      mp_limb_t cy_limb;
+      cy_limb = mpn_lshift (rp, up, abs_usize, -exp % BITS_PER_MP_LIMB);
+      rp[abs_usize] = cy_limb;
+      cy_limb = cy_limb != 0;
+
+      abs_usize += cy_limb;
+      r->_mp_exp = uexp - exp / BITS_PER_MP_LIMB - 1 + cy_limb;
+    }
+  r->_mp_size = usize >= 0 ? abs_usize : -abs_usize;
+}