libgcc/config/picochip/lshrsi3.c

/*

picoChip GCC support for 32-bit logical shift right.

Copyright (C) 2003-2014 Free Software Foundation, Inc.
Contributed by Picochip 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 3, or (at your option) any
later version.

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.

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/>.  */

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 __lshrsi3(USIunion value, HItype count) {
  USIunion result;
  int temp;

  /* 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 < 16) {
    /* Shift low and high words by the count. */
    result.s.low = value.s.low >> count;
    result.s.high = value.s.high >> count;
     
    /* 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. This only works when count isn't zero. */
    if (count != 0) {
      temp = value.s.high << (16 - count);
      result.s.low |= temp;
    }

  } else {
    /* Shift the upper word of the source into the lower word of the
       result, and zero the result's upper word. Note that we actually
       ned to shift by (count - 16), but as we are only using the
       bottom 4 bits, this is equivalent to shifting by count. */
    result.s.low = value.s.high >> count;
    result.s.high = 0;

  }

  return result.l;

}