libgcc/config/picochip/lshrsi3.c

   1 /*
   2
   3 picoChip GCC support for 32-bit logical shift right.
   4
   5 Copyright (C) 2003-2013 Free Software Foundation, Inc.
   6 Contributed by Picochip Ltd.
   7 Maintained by Daniel Towner (daniel.towner@picochip.com)
   8
   9 This file is free software; you can redistribute it and/or modify it
  10 under the terms of the GNU General Public License as published by the
  11 Free Software Foundation; either version 3, or (at your option) any
  12 later version.
  13
  14 This file is distributed in the hope that it will be useful, but
  15 WITHOUT ANY WARRANTY; without even the implied warranty of
  16 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17 General Public License for more details.
  18
  19 Under Section 7 of GPL version 3, you are granted additional
  20 permissions described in the GCC Runtime Library Exception, version
  21 3.1, as published by the Free Software Foundation.
  22
  23 You should have received a copy of the GNU General Public License and
  24 a copy of the GCC Runtime Library Exception along with this program;
  25 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  26 <http://www.gnu.org/licenses/>.  */
  27
  28 typedef int HItype __attribute__ ((mode (HI)));
  29 typedef unsigned int UHItype __attribute__ ((mode (HI)));
  30 typedef unsigned int USItype __attribute__ ((mode (SI)));
  31
  32 typedef struct USIstruct {
  33   UHItype low, high;
  34 } USIstruct;
  35
  36 typedef union USIunion {
  37   USItype l;
  38   USIstruct s;
  39 } USIunion;
  40
  41 USItype __lshrsi3(USIunion value, HItype count) {
  42   USIunion result;
  43   int temp;
  44
  45   /* Ignore a zero count until we get into the (count < 16)
  46      clause. This is slightly slower when shifting by zero, but faster
  47      and smaller in all other cases (due to the better scheduling
  48      opportunities available by putting the test near computational
  49      instructions. */
  50
  51   if (count < 16) {
  52     /* Shift low and high words by the count. */
  53     result.s.low = value.s.low >> count;
  54     result.s.high = value.s.high >> count;
  55
  56     /* There is now a hole in the upper `count' bits of the low
  57        word. Shift the lower `count' bits of the upper word into the
  58        low word. This only works when count isn't zero. */
  59     if (count != 0) {
  60       temp = value.s.high << (16 - count);
  61       result.s.low |= temp;
  62     }
  63
  64   } else {
  65     /* Shift the upper word of the source into the lower word of the
  66        result, and zero the result's upper word. Note that we actually
  67        ned to shift by (count - 16), but as we are only using the
  68        bottom 4 bits, this is equivalent to shifting by count. */
  69     result.s.low = value.s.high >> count;
  70     result.s.high = 0;
  71
  72   }
  73
  74   return result.l;
  75
  76 }