Minor simplification

flanglet · Jan 20, 2024 · 01bda2f · 01bda2f
1 parent 96813f9
commit 01bda2f
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Showing 3 changed files with 13 additions and 9 deletions.
diff --git a/v2/entropy/ANSRangeCodec.go b/v2/entropy/ANSRangeCodec.go
@@ -210,7 +210,7 @@ func (this *ANSRangeEncoder) updateFrequencies(frequencies []int, lr uint) (int,
 			}
 		}
 
-		if err = this.encodeHeader(alphabetSize, alphabet[:], f, lr); err != nil {
+		if err = this.encodeHeader(alphabet[0:alphabetSize], f, lr); err != nil {
 			break
 		}
 
@@ -221,11 +221,13 @@ func (this *ANSRangeEncoder) updateFrequencies(frequencies []int, lr uint) (int,
 }
 
 // Encodes alphabet and frequencies into the bitstream
-func (this *ANSRangeEncoder) encodeHeader(alphabetSize int, alphabet []int, frequencies []int, lr uint) error {
-	if _, err := EncodeAlphabet(this.bitstream, alphabet[0:alphabetSize:256]); err != nil {
+func (this *ANSRangeEncoder) encodeHeader(alphabet []int, frequencies []int, lr uint) error {
+	if _, err := EncodeAlphabet(this.bitstream, alphabet); err != nil {
 		return err
 	}
 
+	alphabetSize := len(alphabet)
+
 	if alphabetSize <= 1 {
 		return nil
 	}

diff --git a/v2/entropy/EntropyUtils.go b/v2/entropy/EntropyUtils.go
@@ -61,7 +61,7 @@ func (this sortByFreq) Swap(i, j int) {
 
 // EncodeAlphabet writes the alphabet to the bitstream and return the number
 // of symbols written or an error.
-// alphabet must be sorted in increasing order
+// alphabet must be composed of values in [0..255] sorted in increasing order
 // alphabet size must be a power of 2 up to 256
 func EncodeAlphabet(obs kanzi.OutputBitStream, alphabet []int) (int, error) {
 	alphabetSize := cap(alphabet)
@@ -164,8 +164,8 @@ func NormalizeFrequencies(freqs []int, alphabet []int, totalFreq, scale int) (in
 
 	// Shortcut
 	if totalFreq == scale {
-		for i, f := range freqs {
-			if f != 0 {
+		for i := 0; i < 256; i++ {
+			if freqs[i] != 0 {
 				alphabet[alphabetSize] = i
 				alphabetSize++
 			}

diff --git a/v2/entropy/RangeCodec.go b/v2/entropy/RangeCodec.go
@@ -113,15 +113,17 @@ func (this *RangeEncoder) updateFrequencies(frequencies []int, size int, lr uint
 		}
 	}
 
-	err = this.encodeHeader(alphabetSize, this.alphabet[:], frequencies, lr)
+	err = this.encodeHeader(this.alphabet[0:alphabetSize], frequencies, lr)
 	return alphabetSize, err
 }
 
-func (this *RangeEncoder) encodeHeader(alphabetSize int, alphabet []int, frequencies []int, lr uint) error {
-	if _, err := EncodeAlphabet(this.bitstream, alphabet[0:alphabetSize]); err != nil {
+func (this *RangeEncoder) encodeHeader(alphabet []int, frequencies []int, lr uint) error {
+	if _, err := EncodeAlphabet(this.bitstream, alphabet); err != nil {
 		return err
 	}
 
+	alphabetSize := len(alphabet)
+
 	if alphabetSize == 0 {
 		return nil
 	}