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114 lines
3.6 KiB
C
114 lines
3.6 KiB
C
/*
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picoChip GCC support for 32-bit arithmetic shift right.
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Copyright (C) 2003, 2004, 2005, 2008, 2009 Free Software Foundation, Inc.
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Contributed by Picochip Ltd.
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Maintained by Daniel Towner (daniel.towner@picochip.com)
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This file is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the
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Free Software Foundation; either version 3, or (at your option) any
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later version.
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This file is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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typedef int HItype __attribute__ ((mode (HI)));
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typedef unsigned int UHItype __attribute__ ((mode (HI)));
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typedef unsigned int USItype __attribute__ ((mode (SI)));
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typedef struct USIstruct {
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UHItype low, high;
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} USIstruct;
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typedef union USIunion {
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USItype l;
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USIstruct s;
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} USIunion;
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USItype __ashrsi3(USIunion value, HItype count) {
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USIunion result;
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int temp;
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int wordOfSignBits;
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/* Ignore a zero count until we get into the (count < 16)
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clause. This is slightly slower when shifting by zero, but faster
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and smaller in all other cases (due to the better scheduling
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opportunities available by putting the test near computational
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instructions. */
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/* if (count == 0) return value.l; */
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if (count < 16) {
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/* Shift low and high words by the count. The high word must use
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an arithmetic shift. There is no arithmetic shift-right by
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variable, so synthesise it. */
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int signWord;
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int reverseCount;
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/* Shift low and high parts by the count. The upper word now has
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invalid signed bits. */
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result.s.low = value.s.low >> count;
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result.s.high = value.s.high >> count;
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if (count != 0) {
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reverseCount = 16 - count;
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/* Given a word of sign bits, shift back left to create the
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destination sign bits. */
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wordOfSignBits = __builtin_asri(value.s.high, 15);
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signWord = wordOfSignBits << reverseCount;
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result.s.high |= signWord;
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/* There is now a hole in the upper `count' bits of the low
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word. Shift the lower `count' bits of the upper word into the
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low word. */
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temp = value.s.high << reverseCount;
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result.s.low |= temp;
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}
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} else {
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int signWord;
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/* Shift is greater than one word, so top word will always be set
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to sign bits, and bottom word will be shifted from top word. */
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result.s.low = value.s.high >> count;
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result.s.high = __builtin_asri(value.s.high, 15);
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if (count != 16) {
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/* Shift the upper word of the source into the lower word of the
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result. Arithmetically shift the upper word as well, to retain
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the sign. This shift must be synthesised, as no such shift
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exists in the instruction set. */
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int signWord;
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/* Given a complete word of sign-bits, shift this back left to
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create the destination sign bits. */
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signWord = result.s.high << (16 - count);
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// signWord = wordOfSignBits << (16 - count);
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/* Insert the sign bits to the result's low word. */
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result.s.low |= signWord;
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}
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}
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return result.l;
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}
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