51 lines
1.9 KiB
C++
51 lines
1.9 KiB
C++
#include "bitpacker.h"
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#include <cmath>
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// Sometimes we can't explicitly define bitfields because we need to allow users to
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// change the size and arrangement of its members. In those cases we use this
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// convenience class to handle packing and unpacking each member.
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BitPacker::BitPacker(uint32_t mask) {
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this->setMask(mask);
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}
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void BitPacker::setMask(uint32_t mask) {
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m_mask = mask;
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// Precalculate the number and positions of the mask bits
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m_setBits.clear();
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for (int i = 0; mask != 0; mask >>= 1, i++)
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if (mask & 1) m_setBits.append(1 << i);
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// For masks with only contiguous bits m_maxValue is equivalent to (m_mask >> n), where n is the number of trailing 0's in m_mask.
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m_maxValue = (m_setBits.length() >= 32) ? UINT_MAX : ((1 << m_setBits.length()) - 1);
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}
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// Given an arbitrary value to set for this bitfield member, returns a bounded value that can later be packed losslessly.
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uint32_t BitPacker::clamp(uint32_t value) const {
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return (m_maxValue == UINT_MAX) ? value : (value % (m_maxValue + 1));
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}
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// Given packed data, returns the extracted value for the bitfield member.
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// For masks with only contiguous bits this is equivalent to ((data & m_mask) >> n), where n is the number of trailing 0's in m_mask.
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uint32_t BitPacker::unpack(uint32_t data) const {
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uint32_t value = 0;
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data &= m_mask;
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for (int i = 0; i < m_setBits.length(); i++) {
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if (data & m_setBits.at(i))
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value |= (1 << i);
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}
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return value;
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}
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// Given a value for the bitfield member, returns the value to OR together with the other members.
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// For masks with only contiguous bits this is equivalent to ((value << n) & m_mask), where n is the number of trailing 0's in m_mask.
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uint32_t BitPacker::pack(uint32_t value) const {
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uint32_t data = 0;
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for (int i = 0; i < m_setBits.length(); i++) {
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if (value == 0) return data;
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if (value & 1) data |= m_setBits.at(i);
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value >>= 1;
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}
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return data;
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}
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