| // Copyright 2013 the V8 project authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #if V8_TARGET_ARCH_ARM64 |
| |
| #include "src/arm64/utils-arm64.h" |
| |
| |
| namespace v8 { |
| namespace internal { |
| |
| #define __ assm-> |
| |
| |
| int CountLeadingZeros(uint64_t value, int width) { |
| // TODO(jbramley): Optimize this for ARM64 hosts. |
| DCHECK((width == 32) || (width == 64)); |
| int count = 0; |
| uint64_t bit_test = 1UL << (width - 1); |
| while ((count < width) && ((bit_test & value) == 0)) { |
| count++; |
| bit_test >>= 1; |
| } |
| return count; |
| } |
| |
| |
| int CountLeadingSignBits(int64_t value, int width) { |
| // TODO(jbramley): Optimize this for ARM64 hosts. |
| DCHECK((width == 32) || (width == 64)); |
| if (value >= 0) { |
| return CountLeadingZeros(value, width) - 1; |
| } else { |
| return CountLeadingZeros(~value, width) - 1; |
| } |
| } |
| |
| |
| int CountTrailingZeros(uint64_t value, int width) { |
| // TODO(jbramley): Optimize this for ARM64 hosts. |
| DCHECK((width == 32) || (width == 64)); |
| int count = 0; |
| while ((count < width) && (((value >> count) & 1) == 0)) { |
| count++; |
| } |
| return count; |
| } |
| |
| |
| int CountSetBits(uint64_t value, int width) { |
| // TODO(jbramley): Would it be useful to allow other widths? The |
| // implementation already supports them. |
| DCHECK((width == 32) || (width == 64)); |
| |
| // Mask out unused bits to ensure that they are not counted. |
| value &= (0xffffffffffffffffUL >> (64-width)); |
| |
| // Add up the set bits. |
| // The algorithm works by adding pairs of bit fields together iteratively, |
| // where the size of each bit field doubles each time. |
| // An example for an 8-bit value: |
| // Bits: h g f e d c b a |
| // \ | \ | \ | \ | |
| // value = h+g f+e d+c b+a |
| // \ | \ | |
| // value = h+g+f+e d+c+b+a |
| // \ | |
| // value = h+g+f+e+d+c+b+a |
| value = ((value >> 1) & 0x5555555555555555) + (value & 0x5555555555555555); |
| value = ((value >> 2) & 0x3333333333333333) + (value & 0x3333333333333333); |
| value = ((value >> 4) & 0x0f0f0f0f0f0f0f0f) + (value & 0x0f0f0f0f0f0f0f0f); |
| value = ((value >> 8) & 0x00ff00ff00ff00ff) + (value & 0x00ff00ff00ff00ff); |
| value = ((value >> 16) & 0x0000ffff0000ffff) + (value & 0x0000ffff0000ffff); |
| value = ((value >> 32) & 0x00000000ffffffff) + (value & 0x00000000ffffffff); |
| |
| return static_cast<int>(value); |
| } |
| |
| |
| uint64_t LargestPowerOf2Divisor(uint64_t value) { |
| return value & -value; |
| } |
| |
| |
| int MaskToBit(uint64_t mask) { |
| DCHECK(CountSetBits(mask, 64) == 1); |
| return CountTrailingZeros(mask, 64); |
| } |
| |
| |
| } // namespace internal |
| } // namespace v8 |
| |
| #endif // V8_TARGET_ARCH_ARM64 |