Moser-De Bruijn-ish nibble expansion lookup

mdbs_lut.h

#include <stdint.h>

static constexpr uint8_t expand2[] = {
	[0b0000] = 0b00000000, [0b0001] = 0b00000001,
	[0b0010] = 0b00000100, [0b0011] = 0b00000101,
	[0b0100] = 0b00010000, [0b0101] = 0b00010001,
	[0b0110] = 0b00010100, [0b0111] = 0b00010101,
	[0b1000] = 0b01000000, [0b1001] = 0b01000001,
	[0b1010] = 0b01000100, [0b1011] = 0b01000101,
	[0b1100] = 0b01010000, [0b1101] = 0b01010001,
	[0b1110] = 0b01010100, [0b1111] = 0b01010101
};

static constexpr uint16_t expand4[] = {
	[0b0000] = 0x0000, [0b0001] = 0x0003,
	[0b0010] = 0x0030, [0b0011] = 0x0033,
	[0b0100] = 0x0300, [0b0101] = 0x0303,
	[0b0110] = 0x0330, [0b0111] = 0x0333,
	[0b1000] = 0x3000, [0b1001] = 0x3003,
	[0b1010] = 0x3030, [0b1011] = 0x3033,
	[0b1100] = 0x3300, [0b1101] = 0x3303,
	[0b1110] = 0x3330, [0b1111] = 0x3333
};

static constexpr uint32_t expand8[] = {
	[0b0000] = 0x00000000, [0b0001] = 0x0000000f,
	[0b0010] = 0x00000f00, [0b0011] = 0x00000f0f,
	[0b0100] = 0x000f0000, [0b0101] = 0x000f000f,
	[0b0110] = 0x000f0f00, [0b0111] = 0x000f0f0f,
	[0b1000] = 0x0f000000, [0b1001] = 0x0f00000f,
	[0b1010] = 0x0f000f00, [0b1011] = 0x0f000f0f,
	[0b1100] = 0x0f0f0000, [0b1101] = 0x0f0f000f,
	[0b1110] = 0x0f0f0f00, [0b1111] = 0x0f0f0f0f
};

static constexpr uint64_t expand16[] = {
	[0b0000] = 0x0000000000000000, [0b0001] = 0x00000000000000ff,
	[0b0010] = 0x0000000000ff0000, [0b0011] = 0x0000000000ff00ff,
	[0b0100] = 0x000000ff00000000, [0b0101] = 0x000000ff000000ff,
	[0b0110] = 0x000000ff00ff0000, [0b0111] = 0x000000ff00ff00ff,
	[0b1000] = 0x00ff000000000000, [0b1001] = 0x00ff0000000000ff,
	[0b1010] = 0x00ff000000ff0000, [0b1011] = 0x00ff000000ff00ff,
	[0b1100] = 0x00ff00ff00000000, [0b1101] = 0x00ff00ff000000ff,
	[0b1110] = 0x00ff00ff00ff0000, [0b1111] = 0x00ff00ff00ff00ff
};