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35 lines
1.2 KiB
C++
35 lines
1.2 KiB
C++
//
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// BitSpread.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 12/10/2021.
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// Copyright © 2021 Thomas Harte. All rights reserved.
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//
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#pragma once
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namespace Numeric {
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/// @returns The bits of @c input with a 0 bit inserted between each and
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/// keeping the least-significant bit in its original position.
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///
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/// i.e. if @c input is abcdefgh then the result is 0a0b0c0d0e0f0g0h
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constexpr uint16_t spread_bits(uint8_t input) {
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uint16_t result = uint16_t(input); // 0000 0000 abcd efgh
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result = (result | (result << 4)) & 0x0f0f; // 0000 abcd 0000 efgh
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result = (result | (result << 2)) & 0x3333; // 00ab 00cd 00ef 00gh
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return (result | (result << 1)) & 0x5555; // 0a0b 0c0d 0e0f 0g0h
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}
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/// Performs the opposite action to @c spread_bits; given the 16-bit input
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/// @c abcd @c efgh @c ijkl @c mnop, returns the byte value @c bdfhjlnp
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/// i.e. every other bit is retained, keeping the least-significant bit in place.
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constexpr uint8_t unspread_bits(uint16_t input) {
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input &= 0x5555; // 0a0b 0c0d 0e0f 0g0h
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input = (input | (input >> 1)) & 0x3333; // 00ab 00cd 00ef 00gh
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input = (input | (input >> 2)) & 0x0f0f; // 0000 abcd 0000 efgh
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return uint8_t(input | (input >> 4)); // 0000 0000 abcd efgh
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}
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}
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