78 lines
3.0 KiB
Java
78 lines
3.0 KiB
Java
package javass.bits;
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import static javass.Preconditions.checkArgument;
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public final class Bits64 {
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private Bits64() {}
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/**
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* Creates a bitmask from a start position to a position defined by start + size -1
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* @param start the index of the first bit of the bitmask
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* @param size the length of the bitmask
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* @throws IllegalArgumentException if start and size don't define a subset of 0 to 63
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* @return the bitmask
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*/
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public static long mask(int start, int size) {
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checkStartSize(start, size);
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if (size == Long.SIZE)
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return ~0;
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else
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return ((1L << size) - 1) << start;
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}
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/**
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* creates a bitstring which has it's size least significant bits equals to those of bits from start to start + size - 1
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* @param bits the starting bitstring
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* @param start the index of the first bit of the bitstring to be extracted
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* @param size of the bitstring to be extracted
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* @throws IllegalArgumentException if start and size don't define a subset of 0 to 63
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* @return a bitstring with the exctracted bitstring from bits as its least significant bits
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*/
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public static long extract(long bits, int start, int size) {
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checkStartSize(start, size);
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return (bits >> (start)) & mask(0, size);
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}
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/**
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* Packs two bitstrings(v1 and v2) together in slots of size s1 and s2
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* @param vi bitsrings to pack
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* @param si size of each slot
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* @throws IllegalArgumentException if vi and si aren't between 1 and 64 and if vi > si and if vi+si>64
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* @return the final bitstring that packs all of the bitstrings together
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*/
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public static long pack(long v1, int s1, long v2, int s2) {
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checkArgument(s1 + s2 <= Long.SIZE);
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checkPack(v1, s1);
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checkPack(v2, s2);
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return (v2 << (s1) ) + v1;
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}
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/**
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* Checks if the arguments of the pack functions are >0 and <Long.SIZE and if the size of the bitstring is less than the slot it's destined to
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* @param v bitstring to check
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* @param s size to check
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* @throws IllegalArgumentException if the conditions are not met
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*/
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private static void checkPack(long v, int s) {
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if(!(s <= Long.SIZE
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&& s >= 1
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&& (mask(0,s) & v)==v ))
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throw new IllegalArgumentException();
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}
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/**
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* Checks if a given start position and size are valid
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* meaning they're positive and less than the max value of {@link Long} or throws an exception.
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* @param start an int that must be positive and inferior to the max value of {@link Long}.
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* @param size an int that must be positive and inferior to the max value of {@link Integer}.
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* @throws IllegalArgumentException if start and size don't define a subset of 0 to 63.
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*/
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private static void checkStartSize(int start, int size) {
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checkArgument(size <= Long.SIZE
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&& size >= 0
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&& start >= 0
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&& start <= Long.SIZE
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&& start + size <= Long.SIZE);
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}
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}
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