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/*
* Copyright (c) 2017, 2019 ARM Limited
* All rights reserved
*
* The license below extends only to copyright in the software and shall
* not be construed as granting a license to any other intellectual
* property including but not limited to intellectual property relating
* to a hardware implementation of the functionality of the software
* licensed hereunder. You may use the software subject to the license
* terms below provided that you ensure that this notice is replicated
* unmodified and in its entirety in all distributions of the software,
* modified or unmodified, in source code or in binary form.
*
* Copyright (c) 2003-2005 The Regents of The University of Michigan
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef __BASE_BITFIELD_HH__
#define __BASE_BITFIELD_HH__
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <type_traits>
namespace gem5
{
extern const uint8_t reverseBitsLookUpTable[];
/**
* Generate a 64-bit mask of 'nbits' 1s, right justified. If a number of bits
* greater than 64 is given, it is truncated to 64.
*
* @param nbits The number of bits set in the mask.
*
* @ingroup api_bitfield
*/
constexpr uint64_t
mask(unsigned nbits)
{
return (nbits >= 64) ? (uint64_t)-1LL : (1ULL << nbits) - 1;
}
/**
* Extract the bitfield from position 'first' to 'last' (inclusive)
* from 'val' and right justify it. MSB is numbered 63, LSB is 0.
*
* @ingroup api_bitfield
*/
template <class T>
constexpr T
bits(T val, unsigned first, unsigned last)
{
assert(first >= last);
int nbits = first - last + 1;
return (val >> last) & mask(nbits);
}
/**
* Extract the bit from this position from 'val' and right justify it.
*
* @ingroup api_bitfield
*/
template <class T>
constexpr T
bits(T val, unsigned bit)
{
return bits(val, bit, bit);
}
/**
* Mask off the given bits in place like bits() but without shifting.
* msb = 63, lsb = 0
*
* @ingroup api_bitfield
*/
template <class T>
constexpr T
mbits(T val, unsigned first, unsigned last)
{
return val & (mask(first + 1) & ~mask(last));
}
/**
* @ingroup api_bitfield
*/
constexpr uint64_t
mask(unsigned first, unsigned last)
{
return mbits((uint64_t)-1LL, first, last);
}
/**
* Sign-extend an N-bit value to 64 bits. Assumes all bits past the sign are
* currently zero. For true sign extension regardless of the value of the sign
* bit, see szext.
*
* @ingroup api_bitfield
*/
template <int N>
constexpr uint64_t
sext(uint64_t val)
{
bool sign_bit = bits(val, N - 1);
if (sign_bit)
val |= ~mask(N);
return val;
}
/**
* Sign-extend an N-bit value to 64 bits. Zero any bits past the sign if
* necessary.
*
* @ingroup api_bitfield
*/
template <int N>
constexpr uint64_t
szext(uint64_t val)
{
bool sign_bit = bits(val, N - 1);
if (sign_bit)
val |= ~mask(N);
else
val &= mask(N);
return val;
}
/**
* Returns val with bits first to last set to the LSBs of bit_val
*
* E.g.:
* first: 7
* last: 4
* val: 0xFFFF
* bit_val: 0x0000
* returned: 0xFF0F
*
* @ingroup api_bitfield
*/
template <class T, class B>
constexpr T
insertBits(T val, unsigned first, unsigned last, B bit_val)
{
assert(first >= last);
T bmask = mask(first, last);
val &= ~bmask;
val |= ((T)bit_val << last) & bmask;
return val;
}
/**
* Overloaded for access to only one bit in value
*
* @ingroup api_bitfield
*/
template <class T, class B>
constexpr T
insertBits(T val, unsigned bit, B bit_val)
{
return insertBits(val, bit, bit, bit_val);
}
/**
* A convenience function to replace bits first to last of val with bit_val
* in place. It is functionally equivalent to insertBits.
*
* \note "first" is the MSB and "last" is the LSB. "first" >= "last"
*
* @ingroup api_bitfield
*/
template <class T, class B>
constexpr void
replaceBits(T& val, unsigned first, unsigned last, B bit_val)
{
val = insertBits(val, first, last, bit_val);
}
/**
* Overloaded function to allow to access only 1 bit
*
* @ingroup api_bitfield
*/
template <class T, class B>
constexpr void
replaceBits(T& val, unsigned bit, B bit_val)
{
val = insertBits(val, bit, bit, bit_val);
}
/**
* Takes a value and returns the bit reversed version.
*
* E.g.:
* val: 0x0303
* returned: 0xc0c0
*
* val: 0x0303
* size: 1
* returned: 0x03c0
*
* Algorithm from:
* http://graphics.stanford.edu/~seander/bithacks.html#ReverseBitsByLookupTable
*
* @param val: variable length value
* @param size: number of bytes to mirror
* @return reversed value
*
* @ingroup api_bitfield
*/
template <class T>
std::enable_if_t<std::is_integral_v<T>, T>
reverseBits(T val, size_t size=sizeof(T))
{
assert(size <= sizeof(T));
if constexpr (sizeof(T) == 1) {
return reverseBitsLookUpTable[val];
} else {
T output = {};
for (size_t byte = 0; byte < size; byte++) {
output = (output << 8) | reverseBitsLookUpTable[val & mask(8)];
val >>= 8;
}
return output;
}
}
/**
* Returns the bit position of the MSB that is set in the input
*
* @ingroup api_bitfield
*/
constexpr int
findMsbSet(uint64_t val)
{
int msb = 0;
if (!val)
return 0;
if (bits(val, 63, 32)) {
msb += 32;
val >>= 32;
}
if (bits(val, 31, 16)) {
msb += 16;
val >>= 16;
}
if (bits(val, 15, 8)) {
msb += 8;
val >>= 8;
}
if (bits(val, 7, 4)) {
msb += 4;
val >>= 4;
}
if (bits(val, 3, 2)) {
msb += 2;
val >>= 2;
}
if (bits(val, 1, 1))
msb += 1;
return msb;
}
/**
* Returns the bit position of the LSB that is set in the input
*
* @ingroup api_bitfield
*/
constexpr int
findLsbSet(uint64_t val)
{
int lsb = 0;
if (!val)
return sizeof(val) * 8;
if (!bits(val, 31, 0)) {
lsb += 32;
val >>= 32;
}
if (!bits(val, 15, 0)) {
lsb += 16;
val >>= 16;
}
if (!bits(val, 7, 0)) {
lsb += 8;
val >>= 8;
}
if (!bits(val, 3, 0)) {
lsb += 4;
val >>= 4;
}
if (!bits(val, 1, 0)) {
lsb += 2;
val >>= 2;
}
if (!bits(val, 0, 0))
lsb += 1;
return lsb;
}
/**
* Returns the number of set ones in the provided value.
* PD algorithm from
* http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
*
* @ingroup api_bitfield
*/
constexpr int
popCount(uint64_t val)
{
#ifndef __has_builtin
# define __has_builtin(foo) 0
#endif
#if defined(__GNUC__) || \
(defined(__clang__) && __has_builtin(__builtin_popcountl))
return __builtin_popcountl(val);
#else
const uint64_t m1 = 0x5555555555555555ULL; // ..010101b
const uint64_t m2 = 0x3333333333333333ULL; // ..110011b
const uint64_t m4 = 0x0f0f0f0f0f0f0f0fULL; // ..001111b
const uint64_t sum = 0x0101010101010101ULL;
val -= (val >> 1) & m1; // 2 bits count -> 2 bits
val = (val & m2) + ((val >> 2) & m2); // 4 bits count -> 4 bits
val = (val + (val >> 4)) & m4; // 8 bits count -> 8 bits
return (val * sum) >> 56; // horizontal sum
#endif // defined(__GNUC__) ||
//(defined(__clang__) && __has_builtin(__builtin_popcountl))
}
/**
* Align to the next highest power of two.
*
* The number passed in is aligned to the next highest power of two,
* if it is not already a power of two. Please note that if 0 is
* passed in, 0 is returned.
*
* This code has been modified from the following:
* http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
*
* @ingroup api_bitfield
*/
constexpr uint64_t
alignToPowerOfTwo(uint64_t val)
{
val--;
val |= val >> 1;
val |= val >> 2;
val |= val >> 4;
val |= val >> 8;
val |= val >> 16;
val |= val >> 32;
val++;
return val;
};
/**
* Count trailing zeros in a 32-bit value.
*
* @param An input value
* @return The number of trailing zeros or 32 if the value is zero.
*
* @ingroup api_bitfield
*/
constexpr int
ctz32(uint32_t value)
{
return value ? __builtin_ctzl(value) : 32;
}
/**
* Count trailing zeros in a 64-bit value.
*
* @param An input value
* @return The number of trailing zeros or 64 if the value is zero.
*
* @ingroup api_bitfield
*/
constexpr int
ctz64(uint64_t value)
{
return value ? __builtin_ctzll(value) : 64;
}
} // namespace gem5
#endif // __BASE_BITFIELD_HH__