improve performance of H264/H265 SPS parsers

pkg/bits/read.go

@@ -5,19 +5,33 @@ import (
 	"fmt"
 )
 
+// HasSpace checks whether buffer has space for N bits.
+func HasSpace(buf []byte, pos int, n int) error {
+	if n > ((len(buf) * 8) - pos) {
+		return fmt.Errorf("not enough bits")
+	}
+	return nil
+}
+
 // ReadBits reads N bits.
 func ReadBits(buf []byte, pos *int, n int) (uint64, error) {
-	if n > ((len(buf) * 8) - *pos) {
-		return 0, fmt.Errorf("not enough bits")
+	err := HasSpace(buf, *pos, n)
+	if err != nil {
+		return 0, err
 	}
 
+	return ReadBitsUnsafe(buf, pos, n), nil
+}
+
+// ReadBitsUnsafe reads N bits.
+func ReadBitsUnsafe(buf []byte, pos *int, n int) uint64 {
 	v := uint64(0)
 
 	res := 8 - (*pos & 0x07)
 	if n < res {
 		v := uint64((buf[*pos>>0x03] >> (res - n)) & (1<<n - 1))
 		*pos += n
-		return v, nil
+		return v
 	}
 
 	v = (v << res) | uint64(buf[*pos>>0x03]&(1<<res-1))
@@ -35,7 +49,7 @@ func ReadBits(buf []byte, pos *int, n int) (uint64, error) {
 		*pos += n
 	}
 
-	return v, nil
+	return v
 }
 
 // ReadGolombUnsigned reads an unsigned golomb-encoded value.
@@ -93,29 +107,17 @@ func ReadGolombSigned(buf []byte, pos *int) (int32, error) {
 
 // ReadFlag reads a boolean flag.
 func ReadFlag(buf []byte, pos *int) (bool, error) {
-	if (len(buf)*8 - *pos) == 0 {
-		return false, fmt.Errorf("not enough bits")
+	err := HasSpace(buf, *pos, 1)
+	if err != nil {
+		return false, err
 	}
 
+	return ReadFlagUnsafe(buf, pos), nil
+}
+
+// ReadFlagUnsafe reads a boolean flag.
+func ReadFlagUnsafe(buf []byte, pos *int) bool {
 	b := (buf[*pos>>0x03] >> (7 - (*pos & 0x07))) & 0x01
 	*pos++
-	return b == 1, nil
-}
-
-// ReadUint8 reads a uint8.
-func ReadUint8(buf []byte, pos *int) (uint8, error) {
-	v, err := ReadBits(buf, pos, 8)
-	return uint8(v), err
-}
-
-// ReadUint16 reads a uint16.
-func ReadUint16(buf []byte, pos *int) (uint16, error) {
-	v, err := ReadBits(buf, pos, 16)
-	return uint16(v), err
-}
-
-// ReadUint32 reads a uint32.
-func ReadUint32(buf []byte, pos *int) (uint32, error) {
-	v, err := ReadBits(buf, pos, 32)
-	return uint32(v), err
+	return b == 1
 }