/*

picoChip GCC support for 32-bit arithmetic shift right.

Copyright (C) 2003, 2004, 2005  Free Software Foundation, Inc.
Contributed by picoChip Designs Ltd.
Maintained by Daniel Towner (daniel.towner@picochip.com)

This file 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 2, or (at your option) any
later version.

In addition to the permissions in the GNU General Public License, the
Free Software Foundation gives you unlimited permission to link the
compiled version of this file into combinations with other programs,
and to distribute those combinations without any restriction coming
from the use of this file.  (The General Public License restrictions
do apply in other respects; for example, they cover modification of
the file, and distribution when not linked into a combine
executable.)

This file 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.

You should have received a copy of the GNU General Public License
along with this program; see the file COPYING.  If not, write to
the Free Software Foundation, 51 Franklin Street, Fifth Floor,
Boston, MA 02110-1301, USA. */

typedef int HItype __attribute__ ((mode (HI)));
typedef unsigned int UHItype __attribute__ ((mode (HI)));
typedef unsigned int USItype __attribute__ ((mode (SI)));

typedef struct USIstruct {
  UHItype low, high;
} USIstruct;

typedef union USIunion {
  USItype l;
  USIstruct s;
} USIunion;

USItype __ashrsi3(USIunion value, HItype count) {
  USIunion result;
  int temp;
  int wordOfSignBits;

  /* Ignore a zero count until we get into the (count < 16)
     clause. This is slightly slower when shifting by zero, but faster
     and smaller in all other cases (due to the better scheduling
     opportunities available by putting the test near computational
     instructions. */
  /* if (count == 0) return value.l; */
  
  if (count < 16) {
    /* Shift low and high words by the count. The high word must use
       an arithmetic shift. There is no arithmetic shift-right by
       variable, so synthesise it. */
    int signWord;
    int reverseCount;

    /* Shift low and high parts by the count. The upper word now has
       invalid signed bits. */
    result.s.low = value.s.low >> count;
    result.s.high = value.s.high >> count;

    if (count != 0) {

      reverseCount = 16 - count;
  
      /* Given a word of sign bits, shift back left to create the
	 destination sign bits. */
      wordOfSignBits = __builtin_asri(value.s.high, 15);
      signWord = wordOfSignBits << reverseCount;
      result.s.high |= signWord;
     
      /* There is now a hole in the upper `count' bits of the low
	 word. Shift the lower `count' bits of the upper word into the
	 low word. */
      temp = value.s.high << reverseCount;
      result.s.low |= temp;
    }

  } else {
    int signWord;

    /* Shift is greater than one word, so top word will always be set
       to sign bits, and bottom word will be shifted from top word. */
    result.s.low = value.s.high >> count;
    result.s.high = __builtin_asri(value.s.high, 15);

    if (count != 16) {

      /* Shift the upper word of the source into the lower word of the
	 result. Arithmetically shift the upper word as well, to retain
	 the sign. This shift must be synthesised, as no such shift
	 exists in the instruction set. */
      int signWord;
 

      /* Given a complete word of sign-bits, shift this back left to
	 create the destination sign bits. */
      signWord = result.s.high << (16 - count);
      //      signWord = wordOfSignBits << (16 - count);

      /* Insert the sign bits to the result's low word. */
      result.s.low |= signWord;

    }

  }

  return result.l;

}
