commons-math-legacy/src/main/java/org/apache/commons/math4/legacy/linear/OpenIntToDoubleHashMap.java [178:337]:
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        final int hash  = hashOf(key);
        int index = hash & mask;
        if (containsKey(key, index)) {
            return values[index];
        }

        if (states[index] == FREE) {
            return missingEntries;
        }

        int j = index;
        for (int perturb = perturb(hash); states[index] != FREE; perturb >>= PERTURB_SHIFT) {
            j = probe(perturb, j);
            index = j & mask;
            if (containsKey(key, index)) {
                return values[index];
            }
        }

        return missingEntries;
    }

    /**
     * Check if a value is associated with a key.
     * @param key key to check
     * @return true if a value is associated with key
     */
    public boolean containsKey(final int key) {

        final int hash  = hashOf(key);
        int index = hash & mask;
        if (containsKey(key, index)) {
            return true;
        }

        if (states[index] == FREE) {
            return false;
        }

        int j = index;
        for (int perturb = perturb(hash); states[index] != FREE; perturb >>= PERTURB_SHIFT) {
            j = probe(perturb, j);
            index = j & mask;
            if (containsKey(key, index)) {
                return true;
            }
        }

        return false;
    }

    /**
     * Get an iterator over map elements.
     * <p>The specialized iterators returned are fail-fast: they throw a
     * <code>ConcurrentModificationException</code> when they detect the map
     * has been modified during iteration.</p>
     * @return iterator over the map elements
     */
    public Iterator iterator() {
        return new Iterator();
    }

    /**
     * Perturb the hash for starting probing.
     * @param hash initial hash
     * @return perturbed hash
     */
    private static int perturb(final int hash) {
        return hash & 0x7fffffff;
    }

    /**
     * Find the index at which a key should be inserted.
     * @param key key to lookup
     * @return index at which key should be inserted
     */
    private int findInsertionIndex(final int key) {
        return findInsertionIndex(keys, states, key, mask);
    }

    /**
     * Find the index at which a key should be inserted.
     * @param keys keys table
     * @param states states table
     * @param key key to lookup
     * @param mask bit mask for hash values
     * @return index at which key should be inserted
     */
    private static int findInsertionIndex(final int[] keys, final byte[] states,
                                          final int key, final int mask) {
        final int hash = hashOf(key);
        int index = hash & mask;
        if (states[index] == FREE) {
            return index;
        } else if (states[index] == FULL && keys[index] == key) {
            return changeIndexSign(index);
        }

        int perturb = perturb(hash);
        int j = index;
        if (states[index] == FULL) {
            while (true) {
                j = probe(perturb, j);
                index = j & mask;
                perturb >>= PERTURB_SHIFT;

                if (states[index] != FULL || keys[index] == key) {
                    break;
                }
            }
        }

        if (states[index] == FREE) {
            return index;
        } else if (states[index] == FULL) {
            // due to the loop exit condition,
            // if (states[index] == FULL) then keys[index] == key
            return changeIndexSign(index);
        }

        final int firstRemoved = index;
        while (true) {
            j = probe(perturb, j);
            index = j & mask;

            if (states[index] == FREE) {
                return firstRemoved;
            } else if (states[index] == FULL && keys[index] == key) {
                return changeIndexSign(index);
            }

            perturb >>= PERTURB_SHIFT;
        }
    }

    /**
     * Compute next probe for collision resolution.
     * @param perturb perturbed hash
     * @param j previous probe
     * @return next probe
     */
    private static int probe(final int perturb, final int j) {
        return (j << 2) + j + perturb + 1;
    }

    /**
     * Change the index sign.
     * @param index initial index
     * @return changed index
     */
    private static int changeIndexSign(final int index) {
        return -index - 1;
    }

    /**
     * Get the number of elements stored in the map.
     * @return number of elements stored in the map
     */
    public int size() {
        return size;
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commons-math-legacy/src/main/java/org/apache/commons/math4/legacy/linear/OpenIntToFieldHashMap.java [190:349]:
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        final int hash  = hashOf(key);
        int index = hash & mask;
        if (containsKey(key, index)) {
            return values[index];
        }

        if (states[index] == FREE) {
            return missingEntries;
        }

        int j = index;
        for (int perturb = perturb(hash); states[index] != FREE; perturb >>= PERTURB_SHIFT) {
            j = probe(perturb, j);
            index = j & mask;
            if (containsKey(key, index)) {
                return values[index];
            }
        }

        return missingEntries;
    }

    /**
     * Check if a value is associated with a key.
     * @param key key to check
     * @return true if a value is associated with key
     */
    public boolean containsKey(final int key) {

        final int hash  = hashOf(key);
        int index = hash & mask;
        if (containsKey(key, index)) {
            return true;
        }

        if (states[index] == FREE) {
            return false;
        }

        int j = index;
        for (int perturb = perturb(hash); states[index] != FREE; perturb >>= PERTURB_SHIFT) {
            j = probe(perturb, j);
            index = j & mask;
            if (containsKey(key, index)) {
                return true;
            }
        }

        return false;
    }

    /**
     * Get an iterator over map elements.
     * <p>The specialized iterators returned are fail-fast: they throw a
     * <code>ConcurrentModificationException</code> when they detect the map
     * has been modified during iteration.</p>
     * @return iterator over the map elements
     */
    public Iterator iterator() {
        return new Iterator();
    }

    /**
     * Perturb the hash for starting probing.
     * @param hash initial hash
     * @return perturbed hash
     */
    private static int perturb(final int hash) {
        return hash & 0x7fffffff;
    }

    /**
     * Find the index at which a key should be inserted.
     * @param key key to lookup
     * @return index at which key should be inserted
     */
    private int findInsertionIndex(final int key) {
        return findInsertionIndex(keys, states, key, mask);
    }

    /**
     * Find the index at which a key should be inserted.
     * @param keys keys table
     * @param states states table
     * @param key key to lookup
     * @param mask bit mask for hash values
     * @return index at which key should be inserted
     */
    private static int findInsertionIndex(final int[] keys, final byte[] states,
                                          final int key, final int mask) {
        final int hash = hashOf(key);
        int index = hash & mask;
        if (states[index] == FREE) {
            return index;
        } else if (states[index] == FULL && keys[index] == key) {
            return changeIndexSign(index);
        }

        int perturb = perturb(hash);
        int j = index;
        if (states[index] == FULL) {
            while (true) {
                j = probe(perturb, j);
                index = j & mask;
                perturb >>= PERTURB_SHIFT;

                if (states[index] != FULL || keys[index] == key) {
                    break;
                }
            }
        }

        if (states[index] == FREE) {
            return index;
        } else if (states[index] == FULL) {
            // due to the loop exit condition,
            // if (states[index] == FULL) then keys[index] == key
            return changeIndexSign(index);
        }

        final int firstRemoved = index;
        while (true) {
            j = probe(perturb, j);
            index = j & mask;

            if (states[index] == FREE) {
                return firstRemoved;
            } else if (states[index] == FULL && keys[index] == key) {
                return changeIndexSign(index);
            }

            perturb >>= PERTURB_SHIFT;
        }
    }

    /**
     * Compute next probe for collision resolution.
     * @param perturb perturbed hash
     * @param j previous probe
     * @return next probe
     */
    private static int probe(final int perturb, final int j) {
        return (j << 2) + j + perturb + 1;
    }

    /**
     * Change the index sign.
     * @param index initial index
     * @return changed index
     */
    private static int changeIndexSign(final int index) {
        return -index - 1;
    }

    /**
     * Get the number of elements stored in the map.
     * @return number of elements stored in the map
     */
    public int size() {
        return size;
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