use mask in bitreader

it's much faster than bit shifting

src/flac_decoder/flac_decoder.cpp

@@ -4,7 +4,7 @@
  * adapted to ESP32
  *
  * Created on: Jul 03,2020
- * Updated on: Feb 10,2023
+ * Updated on: Apr 10,2023
  *
  * Author: Wolle
  *
@@ -80,6 +80,12 @@ void FLACDecoder_FreeBuffers(){
 //----------------------------------------------------------------------------------------------------------------------
 //            B I T R E A D E R
 //----------------------------------------------------------------------------------------------------------------------
+const uint32_t mask[] = {0x00000000, 0x00000001, 0x00000003, 0x00000007, 0x0000000f, 0x0000001f, 0x0000003f,
+                         0x0000007f, 0x000000ff, 0x000001ff, 0x000003ff, 0x000007ff, 0x00000fff, 0x00001fff,
+                         0x00003fff, 0x00007fff, 0x0000ffff, 0x0001ffff, 0x0003ffff, 0x0007ffff, 0x000fffff,
+                         0x001fffff, 0x003fffff, 0x007fffff, 0x00ffffff, 0x01ffffff, 0x03ffffff, 0x07ffffff,
+                         0x0fffffff, 0x1fffffff, 0x3fffffff, 0x7fffffff, 0xffffffff};
+
 uint32_t readUint(uint8_t nBits, int *bytesLeft){
     while (m_bitBufferLen < nBits){
         uint8_t temp = *(m_inptr + m_rIndex);
@@ -92,7 +98,7 @@ uint32_t readUint(uint8_t nBits, int *bytesLeft){
     m_bitBufferLen -= nBits;
     uint32_t result = m_bitBuffer >> m_bitBufferLen;
     if (nBits < 32)
-        result &= (1 << nBits) - 1;
+        result &= mask[nBits];
     return result;
 }
 

src/flac_decoder/flac_decoder.h

@@ -2,7 +2,7 @@
  * flac_decoder.h
  *
  * Created on: Jul 03,2020
- * Updated on: Jan 08,2023
+ * Updated on: Apr 09,2023
  *
  *      Author: wolle
  *