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comparison gcc/config/picochip/libgccExtras/ashrsi3.c @ 0:a06113de4d67

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author kent <kent@cr.ie.u-ryukyu.ac.jp>
date Fri, 17 Jul 2009 14:47:48 +0900
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-1:000000000000 0:a06113de4d67
1 /*
2
3 picoChip GCC support for 32-bit arithmetic shift right.
4
5 Copyright (C) 2003, 2004, 2005, 2008, 2009 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 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 __ashrsi3(USIunion value, HItype count) {
42 USIunion result;
43 int temp;
44 int wordOfSignBits;
45
46 /* Ignore a zero count until we get into the (count < 16)
47 clause. This is slightly slower when shifting by zero, but faster
48 and smaller in all other cases (due to the better scheduling
49 opportunities available by putting the test near computational
50 instructions. */
51 /* if (count == 0) return value.l; */
52
53 if (count < 16) {
54 /* Shift low and high words by the count. The high word must use
55 an arithmetic shift. There is no arithmetic shift-right by
56 variable, so synthesise it. */
57 int signWord;
58 int reverseCount;
59
60 /* Shift low and high parts by the count. The upper word now has
61 invalid signed bits. */
62 result.s.low = value.s.low >> count;
63 result.s.high = value.s.high >> count;
64
65 if (count != 0) {
66
67 reverseCount = 16 - count;
68
69 /* Given a word of sign bits, shift back left to create the
70 destination sign bits. */
71 wordOfSignBits = __builtin_asri(value.s.high, 15);
72 signWord = wordOfSignBits << reverseCount;
73 result.s.high |= signWord;
74
75 /* There is now a hole in the upper `count' bits of the low
76 word. Shift the lower `count' bits of the upper word into the
77 low word. */
78 temp = value.s.high << reverseCount;
79 result.s.low |= temp;
80 }
81
82 } else {
83 int signWord;
84
85 /* Shift is greater than one word, so top word will always be set
86 to sign bits, and bottom word will be shifted from top word. */
87 result.s.low = value.s.high >> count;
88 result.s.high = __builtin_asri(value.s.high, 15);
89
90 if (count != 16) {
91
92 /* Shift the upper word of the source into the lower word of the
93 result. Arithmetically shift the upper word as well, to retain
94 the sign. This shift must be synthesised, as no such shift
95 exists in the instruction set. */
96 int signWord;
97
98
99 /* Given a complete word of sign-bits, shift this back left to
100 create the destination sign bits. */
101 signWord = result.s.high << (16 - count);
102 // signWord = wordOfSignBits << (16 - count);
103
104 /* Insert the sign bits to the result's low word. */
105 result.s.low |= signWord;
106
107 }
108
109 }
110
111 return result.l;
112
113 }