contents of zip

scripts/bit_reader.js

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+// Use strict
+"use strict";
+
+
+// Classes
+
+// Bit reader class
+class BitReader {
+
+	// Public
+
+		// Constructor
+		constructor(data) {
+		
+			// Set data
+			this.data = data;
+			
+			// Initialize byte index
+			this.byteIndex = 0;
+			
+			// Initialize bit index
+			this.bitIndex = 0;
+		}
+		
+		// Get bits
+		getBits(numberOfBits) {
+		
+			// Check if more than one byte is requested
+			if(numberOfBits > Common.BITS_IN_A_BYTE) {
+			
+				// Initialize result
+				var result = 0;
+			
+				// Go through all bytes
+				while(numberOfBits > 0) {
+				
+					// Update result to make space for more bits
+					result <<= Math.min(numberOfBits, Common.BITS_IN_A_BYTE);
+					
+					// Include bits in result
+					result |= this.getBits(Math.min(numberOfBits, Common.BITS_IN_A_BYTE));
+				
+					// Update number of bits
+					numberOfBits -= Common.BITS_IN_A_BYTE;
+				}
+				
+				// Return result
+				return result;
+			}
+			
+			// Otherwise
+			else {
+			
+				// Check if no bits requested
+				if(numberOfBits === 0) {
+				
+					// Return zero
+					return 0;
+				}
+		
+				// Check if number of bits is invalid
+				if(this.byteIndex === this.data["length"] || (this.byteIndex === this.data["length"] - 1 && this.bitIndex + numberOfBits > Common.BITS_IN_A_BYTE)) {
+				
+					// Throw error
+					throw "Invalid number of bits.";
+				}
+			
+				// Initialize result to data at the byte index
+				var result = this.data[this.byteIndex] << Common.BITS_IN_A_BYTE;
+				
+				// Check if more data is needed
+				if(this.bitIndex + numberOfBits > Common.BITS_IN_A_BYTE) {
+				
+					// Append next byte to the result
+					result |= this.data[this.byteIndex + 1];
+				}
+				
+				// Remove upper bits from result
+				result &= (1 << (Common.BITS_IN_A_BYTE * 2 - this.bitIndex)) - 1;
+				
+				// Remove lower bits from result
+				result >>>= (Common.BITS_IN_A_BYTE * 2 - (this.bitIndex + numberOfBits));
+			
+				// Update bit index
+				this.bitIndex += numberOfBits;
+				
+				// Check if bit index overflowed into the next byte
+				if(this.bitIndex >= Common.BITS_IN_A_BYTE) {
+				
+					// Increment byte index
+					++this.byteIndex;
+				
+					// Correct bit index
+					this.bitIndex %= Common.BITS_IN_A_BYTE;
+				}
+				
+				// Return result
+				return result;
+			}
+		}
+		
+		// Get bytes
+		getBytes(numberOfBytes) {
+		
+			// Initialize result
+			var result = new Uint8Array(numberOfBytes);
+			
+			// Go through all bytes
+			for(var i = 0; i < numberOfBytes; ++i) {
+			
+				// Set byte in the result
+				result[i] = this.getBits(Common.BITS_IN_A_BYTE);
+			}
+			
+			// Return result
+			return result;
+		}
+}
+
+
+// Main function
+
+// Set global object's bit reader
+globalThis["BitReader"] = BitReader;