jiuyiUniapp/service/node_modules/image-size/dist/utils/bit-reader.js

45 lines
1.6 KiB
JavaScript

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.BitReader = void 0;
/** This class helps read Uint8Array bit-by-bit */
class BitReader {
constructor(input, endianness) {
this.input = input;
this.endianness = endianness;
// Skip the first 16 bits (2 bytes) of signature
this.byteOffset = 2;
this.bitOffset = 0;
}
/** Reads a specified number of bits, and move the offset */
getBits(length = 1) {
let result = 0;
let bitsRead = 0;
while (bitsRead < length) {
if (this.byteOffset >= this.input.length) {
throw new Error('Reached end of input');
}
const currentByte = this.input[this.byteOffset];
const bitsLeft = 8 - this.bitOffset;
const bitsToRead = Math.min(length - bitsRead, bitsLeft);
if (this.endianness === 'little-endian') {
const mask = (1 << bitsToRead) - 1;
const bits = (currentByte >> this.bitOffset) & mask;
result |= bits << bitsRead;
}
else {
const mask = ((1 << bitsToRead) - 1) << (8 - this.bitOffset - bitsToRead);
const bits = (currentByte & mask) >> (8 - this.bitOffset - bitsToRead);
result = (result << bitsToRead) | bits;
}
bitsRead += bitsToRead;
this.bitOffset += bitsToRead;
if (this.bitOffset === 8) {
this.byteOffset++;
this.bitOffset = 0;
}
}
return result;
}
}
exports.BitReader = BitReader;