Write the bigram frequency following the new formula
This also tests for bigram frequency against unigram frequency
Bug: 6313806
Bug: 6028348
Change-Id: If7faa3559fee9f2496890f0bc0e081279e100854
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
index 4845a33..3c818cc 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
@@ -174,6 +174,7 @@
private static final int MAX_CHARGROUPS_IN_A_NODE = 0x7FFF; // 32767
private static final int MAX_TERMINAL_FREQUENCY = 255;
+ private static final int MAX_BIGRAM_FREQUENCY = 15;
// Arbitrary limit to how much passes we consider address size compression should
// terminate in. At the time of this writing, our largest dictionary completes
@@ -726,12 +727,13 @@
*
* @param more whether there are more bigrams after this one.
* @param offset the offset of the bigram.
- * @param bigramFrequency the frequency of the bigram, 0..15.
- * @param unigramFrequency the unigram frequency of the same word.
+ * @param bigramFrequency the frequency of the bigram, 0..255.
+ * @param unigramFrequency the unigram frequency of the same word, 0..255.
+ * @param word the second bigram, for debugging purposes
* @return the flags
*/
private static final int makeBigramFlags(final boolean more, final int offset,
- final int bigramFrequency, final int unigramFrequency) {
+ int bigramFrequency, final int unigramFrequency, final String word) {
int bigramFlags = (more ? FLAG_ATTRIBUTE_HAS_NEXT : 0)
+ (offset < 0 ? FLAG_ATTRIBUTE_OFFSET_NEGATIVE : 0);
switch (getByteSize(offset)) {
@@ -747,7 +749,21 @@
default:
throw new RuntimeException("Strange offset size");
}
- bigramFlags += bigramFrequency & FLAG_ATTRIBUTE_FREQUENCY;
+ if (unigramFrequency > bigramFrequency) {
+ MakedictLog.e("Unigram freq is superior to bigram freq for \"" + word
+ + "\". Bigram freq is " + bigramFrequency + ", unigram freq for "
+ + word + " is " + unigramFrequency);
+ bigramFrequency = unigramFrequency;
+ }
+ // We compute the difference between 255 (which means probability = 1) and the
+ // unigram score. We split this into discrete 16 steps, and this is the value
+ // we store into the 4 bits of the bigrams frequency.
+ final float bigramRatio = (float)(bigramFrequency - unigramFrequency)
+ / (MAX_TERMINAL_FREQUENCY - unigramFrequency);
+ // TODO: if the bigram freq is very close to the unigram frequency, we don't want
+ // to include the bigram in the binary dictionary at all.
+ final int discretizedFrequency = Math.round(bigramRatio * MAX_BIGRAM_FREQUENCY);
+ bigramFlags += discretizedFrequency & FLAG_ATTRIBUTE_FREQUENCY;
return bigramFlags;
}
@@ -862,7 +878,7 @@
++groupAddress;
final int offset = addressOfBigram - groupAddress;
int bigramFlags = makeBigramFlags(bigramIterator.hasNext(), offset,
- bigram.mFrequency, unigramFrequencyForThisWord);
+ bigram.mFrequency, unigramFrequencyForThisWord, bigram.mWord);
buffer[index++] = (byte)bigramFlags;
final int bigramShift = writeVariableAddress(buffer, index, Math.abs(offset));
index += bigramShift;