gcc/config/picochip/libgccExtras/ashrsi3.c

   1 /*
   2
   3 picoChip GCC support for 32-bit arithmetic shift right.
   4
   5 Copyright (C) 2003, 2004, 2005, 2008  Free Software Foundation, Inc.
   6 Contributed by picoChip Designs 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 2, or (at your option) any
  12 later version.
  13
  14 In addition to the permissions in the GNU General Public License, the
  15 Free Software Foundation gives you unlimited permission to link the
  16 compiled version of this file into combinations with other programs,
  17 and to distribute those combinations without any restriction coming
  18 from the use of this file.  (The General Public License restrictions
  19 do apply in other respects; for example, they cover modification of
  20 the file, and distribution when not linked into a combine
  21 executable.)
  22
  23 This file is distributed in the hope that it will be useful, but
  24 WITHOUT ANY WARRANTY; without even the implied warranty of
  25 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  26 General Public License for more details.
  27
  28 You should have received a copy of the GNU General Public License
  29 along with this program; see the file COPYING.  If not, write to
  30 the Free Software Foundation, 51 Franklin Street, Fifth Floor,
  31 Boston, MA 02110-1301, USA. */
  32
  33 typedef int HItype __attribute__ ((mode (HI)));
  34 typedef unsigned int UHItype __attribute__ ((mode (HI)));
  35 typedef unsigned int USItype __attribute__ ((mode (SI)));
  36
  37 typedef struct USIstruct {
  38   UHItype low, high;
  39 } USIstruct;
  40
  41 typedef union USIunion {
  42   USItype l;
  43   USIstruct s;
  44 } USIunion;
  45
  46 USItype __ashrsi3(USIunion value, HItype count) {
  47   USIunion result;
  48   int temp;
  49   int wordOfSignBits;
  50
  51   /* Ignore a zero count until we get into the (count < 16)
  52      clause. This is slightly slower when shifting by zero, but faster
  53      and smaller in all other cases (due to the better scheduling
  54      opportunities available by putting the test near computational
  55      instructions. */
  56   /* if (count == 0) return value.l; */
  57
  58   if (count < 16) {
  59     /* Shift low and high words by the count. The high word must use
  60        an arithmetic shift. There is no arithmetic shift-right by
  61        variable, so synthesise it. */
  62     int signWord;
  63     int reverseCount;
  64
  65     /* Shift low and high parts by the count. The upper word now has
  66        invalid signed bits. */
  67     result.s.low = value.s.low >> count;
  68     result.s.high = value.s.high >> count;
  69
  70     if (count != 0) {
  71
  72       reverseCount = 16 - count;
  73
  74       /* Given a word of sign bits, shift back left to create the
  75          destination sign bits. */
  76       wordOfSignBits = __builtin_asri(value.s.high, 15);
  77       signWord = wordOfSignBits << reverseCount;
  78       result.s.high |= signWord;
  79
  80       /* There is now a hole in the upper `count' bits of the low
  81          word. Shift the lower `count' bits of the upper word into the
  82          low word. */
  83       temp = value.s.high << reverseCount;
  84       result.s.low |= temp;
  85     }
  86
  87   } else {
  88     int signWord;
  89
  90     /* Shift is greater than one word, so top word will always be set
  91        to sign bits, and bottom word will be shifted from top word. */
  92     result.s.low = value.s.high >> count;
  93     result.s.high = __builtin_asri(value.s.high, 15);
  94
  95     if (count != 16) {
  96
  97       /* Shift the upper word of the source into the lower word of the
  98          result. Arithmetically shift the upper word as well, to retain
  99          the sign. This shift must be synthesised, as no such shift
 100          exists in the instruction set. */
 101       int signWord;
 102
 103
 104       /* Given a complete word of sign-bits, shift this back left to
 105          create the destination sign bits. */
 106       signWord = result.s.high << (16 - count);
 107       //      signWord = wordOfSignBits << (16 - count);
 108
 109       /* Insert the sign bits to the result's low word. */
 110       result.s.low |= signWord;
 111
 112     }
 113
 114   }
 115
 116   return result.l;
 117
 118 }