/* Implementation of the NORM2 intrinsic
   Copyright (C) 2010-2025 Free Software Foundation, Inc.
   Contributed by Tobias Burnus  <burnus@net-b.de>

This file is part of the GNU Fortran runtime library (libgfortran).

Libgfortran is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public
License as published by the Free Software Foundation; either
version 3 of the License, or (at your option) any later version.

Libgfortran 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 General Public License for more details.

Under Section 7 of GPL version 3, you are granted additional
permissions described in the GCC Runtime Library Exception, version
3.1, as published by the Free Software Foundation.

You should have received a copy of the GNU General Public License and
a copy of the GCC Runtime Library Exception along with this program;
see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
<http://www.gnu.org/licenses/>.  */

#include "libgfortran.h"


#if defined (HAVE_GFC_REAL_8) && defined (HAVE_GFC_REAL_8) && defined (HAVE_SQRT) && defined (HAVE_FABS)

#define MATHFUNC(funcname) funcname


extern void norm2_r8 (gfc_array_r8 * const restrict,
	gfc_array_r8 * const restrict, const index_type * const restrict);
export_proto(norm2_r8);

void
norm2_r8 (gfc_array_r8 * const restrict retarray,
	gfc_array_r8 * const restrict array,
	const index_type * const restrict pdim)
{
  index_type count[GFC_MAX_DIMENSIONS];
  index_type extent[GFC_MAX_DIMENSIONS];
  index_type sstride[GFC_MAX_DIMENSIONS];
  index_type dstride[GFC_MAX_DIMENSIONS];
  const GFC_REAL_8 * restrict base;
  GFC_REAL_8 * restrict dest;
  index_type rank;
  index_type n;
  index_type len;
  index_type delta;
  index_type dim;
  int continue_loop;

  /* Make dim zero based to avoid confusion.  */
  rank = GFC_DESCRIPTOR_RANK (array) - 1;
  dim = (*pdim) - 1;

  if (unlikely (dim < 0 || dim > rank))
    {
      runtime_error ("Dim argument incorrect in NORM intrinsic: "
 		     "is %ld, should be between 1 and %ld",
		     (long int) dim + 1, (long int) rank + 1);
    }

  len = GFC_DESCRIPTOR_EXTENT(array,dim);
  if (len < 0)
    len = 0;
  delta = GFC_DESCRIPTOR_STRIDE(array,dim);

  for (n = 0; n < dim; n++)
    {
      sstride[n] = GFC_DESCRIPTOR_STRIDE(array,n);
      extent[n] = GFC_DESCRIPTOR_EXTENT(array,n);

      if (extent[n] < 0)
	extent[n] = 0;
    }
  for (n = dim; n < rank; n++)
    {
      sstride[n] = GFC_DESCRIPTOR_STRIDE(array, n + 1);
      extent[n] = GFC_DESCRIPTOR_EXTENT(array, n + 1);

      if (extent[n] < 0)
	extent[n] = 0;
    }

  if (retarray->base_addr == NULL)
    {
      size_t alloc_size, str;

      for (n = 0; n < rank; n++)
	{
	  if (n == 0)
	    str = 1;
	  else
	    str = GFC_DESCRIPTOR_STRIDE(retarray,n-1) * extent[n-1];

	  GFC_DIMENSION_SET(retarray->dim[n], 0, extent[n] - 1, str);

	}

      retarray->offset = 0;
      retarray->dtype.rank = rank;

      alloc_size = GFC_DESCRIPTOR_STRIDE(retarray,rank-1) * extent[rank-1];

      retarray->base_addr = xmallocarray (alloc_size, sizeof (GFC_REAL_8));
      if (alloc_size == 0)
	return;
    }
  else
    {
      if (rank != GFC_DESCRIPTOR_RANK (retarray))
	runtime_error ("rank of return array incorrect in"
		       " NORM intrinsic: is %ld, should be %ld",
		       (long int) (GFC_DESCRIPTOR_RANK (retarray)),
		       (long int) rank);

      if (unlikely (compile_options.bounds_check))
	bounds_ifunction_return ((array_t *) retarray, extent,
				 "return value", "NORM");
    }

  for (n = 0; n < rank; n++)
    {
      count[n] = 0;
      dstride[n] = GFC_DESCRIPTOR_STRIDE(retarray,n);
      if (extent[n] <= 0)
	return;
    }

  base = array->base_addr;
  dest = retarray->base_addr;

  continue_loop = 1;
  while (continue_loop)
    {
      const GFC_REAL_8 * restrict src;
      GFC_REAL_8 result;
      src = base;
      {

	GFC_REAL_8 scale;
	result = 0;
	scale = 1;
	if (len <= 0)
	  *dest = 0;
	else
	  {
#if ! defined HAVE_BACK_ARG
	    for (n = 0; n < len; n++, src += delta)
	      {
#endif

	  if (*src != 0)
	    {
	      GFC_REAL_8 absX, val;
	      absX = MATHFUNC(fabs) (*src);
	      if (scale < absX)
		{
		  val = scale / absX;
		  result = 1 + result * val * val;
		  scale = absX;
		}
	      else
		{
		  val = absX / scale;
		  result += val * val;
		}
	    }
	      }
	    result = scale * MATHFUNC(sqrt) (result);
	    *dest = result;
	  }
      }
      /* Advance to the next element.  */
      count[0]++;
      base += sstride[0];
      dest += dstride[0];
      n = 0;
      while (count[n] == extent[n])
	{
	  /* When we get to the end of a dimension, reset it and increment
	     the next dimension.  */
	  count[n] = 0;
	  /* We could precalculate these products, but this is a less
	     frequently used path so probably not worth it.  */
	  base -= sstride[n] * extent[n];
	  dest -= dstride[n] * extent[n];
	  n++;
	  if (n >= rank)
	    {
	      /* Break out of the loop.  */
	      continue_loop = 0;
	      break;
	    }
	  else
	    {
	      count[n]++;
	      base += sstride[n];
	      dest += dstride[n];
	    }
	}
    }
}

#endif