Prepare for radical source tree reorganization. zack/build-layout-experiment

All top-level files and directories are moved into a temporary storage
directory, REORG.TODO, except for files that will certainly still
exist in their current form at top level when we're done (COPYING,
COPYING.LIB, LICENSES, NEWS, README), all old ChangeLog files (which
are moved to the new directory OldChangeLogs, instead), and the
generated file INSTALL (which is just deleted; in the new order, there
will be no generated files checked into version control).

1 files changed, 199 insertions, 0 deletions

diff --git a/REORG.TODO/stdlib/divmod_1.c b/REORG.TODO/stdlib/divmod_1.c
new file mode 100644
index 0000000000..1ef15d6a1e
--- /dev/null
+++ b/REORG.TODO/stdlib/divmod_1.c
@@ -0,0 +1,199 @@
+/* mpn_divmod_1(quot_ptr, dividend_ptr, dividend_size, divisor_limb) --
+   Divide (DIVIDEND_PTR,,DIVIDEND_SIZE) by DIVISOR_LIMB.
+   Write DIVIDEND_SIZE limbs of quotient at QUOT_PTR.
+   Return the single-limb remainder.
+   There are no constraints on the value of the divisor.
+
+   QUOT_PTR and DIVIDEND_PTR might point to the same limb.
+
+Copyright (C) 1991-2017 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 Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 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 Lesser General Public
+License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with the GNU MP Library; see the file COPYING.LIB.  If not, see
+<http://www.gnu.org/licenses/>.  */
+
+#include <gmp.h>
+#include "gmp-impl.h"
+#include "longlong.h"
+
+#ifndef UMUL_TIME
+#define UMUL_TIME 1
+#endif
+
+#ifndef UDIV_TIME
+#define UDIV_TIME UMUL_TIME
+#endif
+
+/* FIXME: We should be using invert_limb (or invert_normalized_limb)
+   here (not udiv_qrnnd).  */
+
+mp_limb_t
+mpn_divmod_1 (mp_ptr quot_ptr,
+	      mp_srcptr dividend_ptr, mp_size_t dividend_size,
+	      mp_limb_t divisor_limb)
+{
+  mp_size_t i;
+  mp_limb_t n1, n0, r;
+  mp_limb_t dummy __attribute__ ((unused));
+
+  /* ??? Should this be handled at all?  Rely on callers?  */
+  if (dividend_size == 0)
+    return 0;
+
+  /* If multiplication is much faster than division, and the
+     dividend is large, pre-invert the divisor, and use
+     only multiplications in the inner loop.  */
+
+  /* This test should be read:
+       Does it ever help to use udiv_qrnnd_preinv?
+	 && Does what we save compensate for the inversion overhead?  */
+  if (UDIV_TIME > (2 * UMUL_TIME + 6)
+      && (UDIV_TIME - (2 * UMUL_TIME + 6)) * dividend_size > UDIV_TIME)
+    {
+      int normalization_steps;
+
+      count_leading_zeros (normalization_steps, divisor_limb);
+      if (normalization_steps != 0)
+	{
+	  mp_limb_t divisor_limb_inverted;
+
+	  divisor_limb <<= normalization_steps;
+
+	  /* Compute (2**2N - 2**N * DIVISOR_LIMB) / DIVISOR_LIMB.  The
+	     result is a (N+1)-bit approximation to 1/DIVISOR_LIMB, with the
+	     most significant bit (with weight 2**N) implicit.  */
+
+	  /* Special case for DIVISOR_LIMB == 100...000.  */
+	  if (divisor_limb << 1 == 0)
+	    divisor_limb_inverted = ~(mp_limb_t) 0;
+	  else
+	    udiv_qrnnd (divisor_limb_inverted, dummy,
+			-divisor_limb, 0, divisor_limb);
+
+	  n1 = dividend_ptr[dividend_size - 1];
+	  r = n1 >> (BITS_PER_MP_LIMB - normalization_steps);
+
+	  /* Possible optimization:
+	     if (r == 0
+	     && divisor_limb > ((n1 << normalization_steps)
+			     | (dividend_ptr[dividend_size - 2] >> ...)))
+	     ...one division less... */
+
+	  for (i = dividend_size - 2; i >= 0; i--)
+	    {
+	      n0 = dividend_ptr[i];
+	      udiv_qrnnd_preinv (quot_ptr[i + 1], r, r,
+				 ((n1 << normalization_steps)
+				  | (n0 >> (BITS_PER_MP_LIMB - normalization_steps))),
+				 divisor_limb, divisor_limb_inverted);
+	      n1 = n0;
+	    }
+	  udiv_qrnnd_preinv (quot_ptr[0], r, r,
+			     n1 << normalization_steps,
+			     divisor_limb, divisor_limb_inverted);
+	  return r >> normalization_steps;
+	}
+      else
+	{
+	  mp_limb_t divisor_limb_inverted;
+
+	  /* Compute (2**2N - 2**N * DIVISOR_LIMB) / DIVISOR_LIMB.  The
+	     result is a (N+1)-bit approximation to 1/DIVISOR_LIMB, with the
+	     most significant bit (with weight 2**N) implicit.  */
+
+	  /* Special case for DIVISOR_LIMB == 100...000.  */
+	  if (divisor_limb << 1 == 0)
+	    divisor_limb_inverted = ~(mp_limb_t) 0;
+	  else
+	    udiv_qrnnd (divisor_limb_inverted, dummy,
+			-divisor_limb, 0, divisor_limb);
+
+	  i = dividend_size - 1;
+	  r = dividend_ptr[i];
+
+	  if (r >= divisor_limb)
+	    r = 0;
+	  else
+	    {
+	      quot_ptr[i] = 0;
+	      i--;
+	    }
+
+	  for (; i >= 0; i--)
+	    {
+	      n0 = dividend_ptr[i];
+	      udiv_qrnnd_preinv (quot_ptr[i], r, r,
+				 n0, divisor_limb, divisor_limb_inverted);
+	    }
+	  return r;
+	}
+    }
+  else
+    {
+      if (UDIV_NEEDS_NORMALIZATION)
+	{
+	  int normalization_steps;
+
+	  count_leading_zeros (normalization_steps, divisor_limb);
+	  if (normalization_steps != 0)
+	    {
+	      divisor_limb <<= normalization_steps;
+
+	      n1 = dividend_ptr[dividend_size - 1];
+	      r = n1 >> (BITS_PER_MP_LIMB - normalization_steps);
+
+	      /* Possible optimization:
+		 if (r == 0
+		 && divisor_limb > ((n1 << normalization_steps)
+				 | (dividend_ptr[dividend_size - 2] >> ...)))
+		 ...one division less... */
+
+	      for (i = dividend_size - 2; i >= 0; i--)
+		{
+		  n0 = dividend_ptr[i];
+		  udiv_qrnnd (quot_ptr[i + 1], r, r,
+			      ((n1 << normalization_steps)
+			       | (n0 >> (BITS_PER_MP_LIMB - normalization_steps))),
+			      divisor_limb);
+		  n1 = n0;
+		}
+	      udiv_qrnnd (quot_ptr[0], r, r,
+			  n1 << normalization_steps,
+			  divisor_limb);
+	      return r >> normalization_steps;
+	    }
+	}
+      /* No normalization needed, either because udiv_qrnnd doesn't require
+	 it, or because DIVISOR_LIMB is already normalized.  */
+
+      i = dividend_size - 1;
+      r = dividend_ptr[i];
+
+      if (r >= divisor_limb)
+	r = 0;
+      else
+	{
+	  quot_ptr[i] = 0;
+	  i--;
+	}
+
+      for (; i >= 0; i--)
+	{
+	  n0 = dividend_ptr[i];
+	  udiv_qrnnd (quot_ptr[i], r, r, n0, divisor_limb);
+	}
+      return r;
+    }
+}