feat: CeilLog2 function

CHANGELOG.md

@@ -12,16 +12,16 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `stpp` box handles optional empty lists properly (a single zero byte)
 - AVC slice size value
 
+### Added
+
+- Exported function: bits.CeilLog2
+
 ## [0.34.1] - 2023-03-09
 
 ### Fixed
 
 - Only start new segment at start or styp box
 
-### Changed
-
--
-
 ## [0.34.0] - 2023-02-28
 
 ### Added

avc/pps.go

@@ -87,7 +87,7 @@ func ParsePPSNALUnit(data []byte, spsMap map[uint32]*SPS) (*PPS, error) {
 			pps.SliceGroupChangeRateMinus1 = reader.ReadExpGolomb()
 		case 6:
 			// slice_group_id[i] has Ceil(Log2(num_slice_groups_minus1 +1) bits)
-			nrBits := ceilLog2(pps.NumSliceGroupsMinus1 + 1)
+			nrBits := bits.CeilLog2(pps.NumSliceGroupsMinus1 + 1)
 
 			for iGroup := uint(0); iGroup <= pps.NumSliceGroupsMinus1; iGroup++ {
 				sgi := reader.Read(nrBits)
@@ -170,14 +170,3 @@ func ParsePPSNALUnit(data []byte, spsMap map[uint32]*SPS) (*PPS, error) {
 	}
 	return pps, nil
 }
-
-// ceilLog2 - nr bits needed to represent numbers 0 - n-1 values
-func ceilLog2(n uint) int {
-	for i := 0; i < 32; i++ {
-		maxNr := uint(1 << i)
-		if maxNr >= n {
-			return i
-		}
-	}
-	return 32
-}

bits/log2.go

@@ -0,0 +1,12 @@
+package bits
+
+// CeilLog2 returns nr bits needed to represent numbers 0 - n-1.
+func CeilLog2(n uint) int {
+	for i := 0; i < 32; i++ {
+		maxNr := uint(1 << i)
+		if maxNr >= n {
+			return i
+		}
+	}
+	return 32
+}

bits/log2_test.go

@@ -0,0 +1,27 @@
+package bits_test
+
+import (
+	"testing"
+
+	"github.com/Eyevinn/mp4ff/bits"
+)
+
+func TestCeilLog2(t *testing.T) {
+	testCases := []struct {
+		n    uint
+		want int
+	}{
+		{0, 0},
+		{1, 0},
+		{2, 1},
+		{3, 2},
+		{4, 2},
+		{5, 3},
+		{128, 7},
+	}
+	for _, tc := range testCases {
+		if got := bits.CeilLog2(tc.n); got != tc.want {
+			t.Errorf("CeilLog2(%d) = %d, want %d", tc.n, got, tc.want)
+		}
+	}
+}