144 lines
4.4 KiB
C++
144 lines
4.4 KiB
C++
// Copyright 2015, ARM Limited
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are met:
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//
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// * Redistributions of source code must retain the above copyright notice,
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// this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above copyright notice,
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// this list of conditions and the following disclaimer in the documentation
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// and/or other materials provided with the distribution.
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// * Neither the name of ARM Limited nor the names of its contributors may be
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// used to endorse or promote products derived from this software without
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// specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS CONTRIBUTORS "AS IS" AND
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// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
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// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#include "compiler-intrinsics.h"
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namespace vixl {
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int CountLeadingSignBitsFallBack(int64_t value, int width) {
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VIXL_ASSERT(IsPowerOf2(width) && (width <= 64));
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if (value >= 0) {
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return CountLeadingZeros(value, width) - 1;
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} else {
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return CountLeadingZeros(~value, width) - 1;
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}
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}
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int CountLeadingZerosFallBack(uint64_t value, int width) {
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VIXL_ASSERT(IsPowerOf2(width) && (width <= 64));
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if (value == 0) {
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return width;
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}
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int count = 0;
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value = value << (64 - width);
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if ((value & UINT64_C(0xffffffff00000000)) == 0) {
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count += 32;
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value = value << 32;
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}
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if ((value & UINT64_C(0xffff000000000000)) == 0) {
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count += 16;
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value = value << 16;
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}
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if ((value & UINT64_C(0xff00000000000000)) == 0) {
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count += 8;
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value = value << 8;
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}
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if ((value & UINT64_C(0xf000000000000000)) == 0) {
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count += 4;
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value = value << 4;
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}
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if ((value & UINT64_C(0xc000000000000000)) == 0) {
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count += 2;
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value = value << 2;
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}
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if ((value & UINT64_C(0x8000000000000000)) == 0) {
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count += 1;
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}
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count += (value == 0);
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return count;
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}
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int CountSetBitsFallBack(uint64_t value, int width) {
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VIXL_ASSERT(IsPowerOf2(width) && (width <= 64));
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// Mask out unused bits to ensure that they are not counted.
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value &= (UINT64_C(0xffffffffffffffff) >> (64 - width));
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// Add up the set bits.
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// The algorithm works by adding pairs of bit fields together iteratively,
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// where the size of each bit field doubles each time.
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// An example for an 8-bit value:
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// Bits: h g f e d c b a
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// \ | \ | \ | \ |
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// value = h+g f+e d+c b+a
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// \ | \ |
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// value = h+g+f+e d+c+b+a
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// \ |
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// value = h+g+f+e+d+c+b+a
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const uint64_t kMasks[] = {
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UINT64_C(0x5555555555555555),
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UINT64_C(0x3333333333333333),
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UINT64_C(0x0f0f0f0f0f0f0f0f),
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UINT64_C(0x00ff00ff00ff00ff),
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UINT64_C(0x0000ffff0000ffff),
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UINT64_C(0x00000000ffffffff),
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};
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for (unsigned i = 0; i < (sizeof(kMasks) / sizeof(kMasks[0])); i++) {
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int shift = 1 << i;
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value = ((value >> shift) & kMasks[i]) + (value & kMasks[i]);
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}
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return static_cast<int>(value);
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}
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int CountTrailingZerosFallBack(uint64_t value, int width) {
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VIXL_ASSERT(IsPowerOf2(width) && (width <= 64));
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int count = 0;
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value = value << (64 - width);
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if ((value & UINT64_C(0xffffffff)) == 0) {
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count += 32;
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value = value >> 32;
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}
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if ((value & 0xffff) == 0) {
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count += 16;
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value = value >> 16;
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}
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if ((value & 0xff) == 0) {
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count += 8;
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value = value >> 8;
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}
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if ((value & 0xf) == 0) {
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count += 4;
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value = value >> 4;
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}
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if ((value & 0x3) == 0) {
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count += 2;
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value = value >> 2;
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}
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if ((value & 0x1) == 0) {
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count += 1;
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}
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count += (value == 0);
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return count - (64 - width);
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}
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} // namespace vixl
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